RECONSTRUCTING INFANT DIET AND WEANING BEHAVIOR OF ANCIENT MAYA FROM LAMANAI, BELIZE USING LASER...

RECONSTRUCTING INFANT DIET AND WEANING BEHAVIOR

OF ANCIENT MAYA FROM LAMANAI, BELIZE

USING LASER ABLATION-INDUCTIVELY COUPLED

PLASMA-MASS SPECTROMETRY

(LA-ICP-MS)

A Dissertation Presented

by

RHAN-JU SONG

Submitted to the Graduate School of the

University of Massachusetts Amherst in partial fulfillment

of the requirements for the degree of

DOCTOR OF PHILOSOPHY

September 2004

Anthropology

RECONSTRUCTING INFANT DIET AND WEANING BEHAVIOR

OF ANCIENT MAYA FROM LAMANAI, BELIZE

USING LASER ABLATION-INDUCTIVELY COUPLED

PLASMA-MASS SPECTROMETRY

(LA-ICP-MS)

A Dissertation Presented

by

RHAN-JU SONG

Approved as to style and content by:

Alan H. Goodman, Chair

Dulasari Amarasiriwardena, Member

R. Brooke Thomas, Member

Ralph Faulkingham, Department Chair

Anthropology

DEDICATION

To my family.

ACKNOWLEDGMENTS

The end of a journey is a contemplative occasion. When one finally arrives at the

intended destination, reflection always competes with relief and happiness to crowd one’s

emotions. Like most lengthy trips, this dissertation has been shaped by the assistance,

experience, inspiration and insight of many individuals.

Foremost, this research has been nurtured by Dr. Alan H. Goodman (Hampshire

College), who has been the most encouraging, flexible and patient advisor since I first

emailed him in 1996. I thank him immensely for his enthusiastic support, which never

wavered, even as I moved to farther destinations. The other members of my committee,

Drs. Dula Amarasiriwardena, Brooke Thomas, as well as Drs. Debra Martin and Alan

Swedlund, are equally acknowledged for their wisdom, understanding, and friendship.

They continue to broaden my perspective and enlighten my approach.

I also thank Deb Martin for her enormous generosity, particularly her support and

willingness to accommodate my personal circumstances. Pete and I only hope that we

have provided plenty of amusing memories in return!

At the Department of Anthropology, I have benefited considerably from the academic

contributions of the faculty and I am proud to be associated with them. As well, I am

grateful to Shelley Bellor Richotte for help with many of the “Fifty Three Easy Steps”.

Fellow grad students have also furthered my education and research objectives. These

wonderful friends, who selflessly offered logistical support in many instances, include

Joseph Jones, Sacha Page, Ventura Perez, Flavia Stanley and Pam Stone. Ventura Perez

and Kathleen Brown Perez are especially thanked for their generous assistance,

indubitable character, and committed friendship.

v

At Hampshire College, my analysis was facilitated by Sue Keydel, Laurie Smith and

Kristin Shrout, who provided invaluable logistical assistance with the LA-ICP-MS

machinery, as well as access to computers and other equipment. Other individuals who

provided important research advice include Drs. Christine White, Lori Wright, Peter

Outridge, Don Reid, Louise Humphrey, Phil Kelleher and John Reid.

For the privilege of analyzing ancient Maya human remains, I owe immense thanks to

several individuals: Drs. Jaime Awe and Allan Moore, of the Belize Department of

Archaeology; Drs. Elizabeth Graham and David M. Pendergast, principal investigators of

the Lamanai Archaeological Project; and Drs. Hermann Helmuth and Paul F. Healy from

the Dept. of Anthropology at Trent University. Funding for this research was generously

provided by the Graduate School at the University of Massachusetts and the Wenner-

Gren Foundation for Anthropological Research and they are duly recognized.

Above all, I am grateful to my family for their infinite love, steadfast support and

patience. This remarkable bunch includes Kim, Nak, Ba, Christine, Dennis and Pete,

who have been the steady keel of my sometimes-flagging ship. This manuscript could

not have been completed without their involvement and I am forever indebted to them.

My husband, Peter A. Zubrzycki, was there when I formulated this research, when we

prepared the first tooth for analysis, and he continues to provide endless support. I thank

him wholeheartedly. During this undertaking, we have traveled from Amherst to

Toronto, driven through North and Central America to live in the jungles of Belize, criss-

crossed the Atlantic innumerable times and confronted many challenges together. This

document is as much a product of his participation and encouragement, and he remains

my most worthy partner in this journey.

vi

vii

ABSTRACT

RECONSTRUCTING INFANT DIET AND WEANING BEHAVIOR OF

ANCIENT MAYA FROM LAMANAI, BELIZE USING LASER ABLATION-

INDUCTIVELY COUPLED PLASMA-MASS SPECTROMETRY (LA-ICP-MS)

SEPTEMBER 2004

RHAN-JU SONG, B.A., UNIVERSITY OF TORONTO

M.A., TRENT UNIVERSITY

Ph.D., UNIVERSITY OF MASSACHUSETTS AMHERST

Directed by: Professor Alan H. Goodman

This investigation represents the first extensive application of Laser Ablation-

Inductively Coupled Plasma-Mass Spectrometry to ancient dental analysis and

paleodietary reconstruction. Enamel strontium composition is examined because it is a

reliable hard tissue indicator of diet during enamel formation in childhood.

Here, infant diet and weaning behavior of pre-contact and colonial period Maya from

Lamanai, Belize are reconstructed. Weaning is a critical dietary transition that has

adaptive significance for later life. Since the strontium-calcium (Sr/Ca) ratio of solid

food is high compared to that of breast milk, strontium composition of hard tissues

developing before, and after, food supplementation can infer the timing of food

introduction and weaning. Known timing of permanent enamel development allows

correlation of canine enamel Sr/Ca values with age in childhood, which is facilitated by

continuous laser microsampling.

viii

The results indicate that enamel Sr/Ca faithfully records a biogenic signal associated

with childhood dietary intake. The total Sr/Ca pattern generally follows the projected

model of strontium change, with food supplementation starting at around nine months of

age, which increases gradually until there is a substantial surge in food intake at

approximately two years of age. Lamanai children continue to nurse afterward, possibly

up to five years of age, but it comprises a minor nutritional component.

Significantly, the disadvantaged colonial Maya cohort has a reduced Sr/Ca pattern

compared to elite Postclassic Maya, suggesting that colonial children may have

exclusively breastfed for longer, delaying the age of food supplementation and weaning.

Colonial Maya also exhibit greater Sr/Ca variation, reflecting dietary shifts that can be

attributed to poorer nutrition and health. Female economic responsibilities partially

account for the differences in colonial childcare practices. Additionally, enamel variation

may reflect the different childhood origins (and weaning patterns) of possible migrants at

Lamanai. Ultimately, the nature of infant diet and enamel Sr/Ca can be linked to

interrelated ecological, political and economic factors.

LA-ICP-MS analysis reveals enamel Sr/Ca to be a sensitive gauge of the prolonged

and complex process of weaning and it proves to be an ideal method of capturing the

richness of early life history documented in sequentially-formed enamel.

ix

TABLE OF CONTENTS

Page

ACKNOWLEDGMENTS ……………………………………………………………….. v

ABSTRACT ……………………………………………………………………………. vii

LIST OF TABLES ……………………………………………………………………... xii

LIST OF FIGURES …………………………………………………………………….. xv

CHAPTER

1. INTRODUCTION TO RESEARCH.……………………………………………….... 1

1.1 Introduction…………………………………………………………….... 1

1.2 Cultural Context Of The Investigation……………………………….…. 6

1.3 Theoretical Framework…………………………………………….……. 7

2. THE MAYA OF LAMANAI, BELIZE.……………………………………………... 9

2.1 Lamanai Research History.…………………………………………….... 9

2.2 Environmental Setting.………………………………………………… 12

2.3 The Nature of Human Settlement at Lamanai.………………………… 14

2.4 Food Resources.………………………………………………………... 18

2.5 The Postclassic and Historical Periods at Lamanai....…………………. 19

2.6 The Biological Consequences of Maya-Spanish Contact at Lamanai..... 33

2.7 Bone Chemical Evidence of Diet at Lamanai………………………….. 40

2.8 The Repercussions of Maya-Spanish Contact on Infant Nutrition…….. 42

3. DENTAL HARD TISSUES AND THEIR APPLICATION

IN PALEONUTRITIONAL RESEARCH…………………………………………. 45

3.1 Dental Anthropology in Archaeological and

Paleonutritional Reconstruction.……………………………………….. 45

3.2 Dental Hard Tissues and Enamel Development.………………………. 49

3.3 Dental Enamel Composition.…………………………………………... 57

3.4 Diagenesis and Hard Tissue Preservation.……………………………... 61

3.5 The Nature of Hard Tissue Preservation at Lamanai.………………….. 67

x

4. THE ROLE OF STRONTIUM ANALYSIS IN PALEONUTRITION…………….. 70

4.1 Strontium Distribution in the Food Web.……………………………… 70

4.2 The Role of Strontium in Human Nutrition.…………………………… 83

4.3 Strontium Absorption and Hard Tissue Incorporation.…………………84

4.4 Variations in Strontium Absorption.…………………………………… 88

4.5 Applicability of Strontium in Hard Tissue Paleodietary Analysis.……. 98

4.6 Strontium Preservation in Fossilized Hard Tissues.…………………...100

4.7 The Effects of Maize Processing on Hard Tissue Sr/Ca Composition.. 102

5. BREASTFEEDING, WEANING AND INFANT HEALTH……………………… 108

5.1 The Nutritional Qualities of Human Breast Milk.…………………….. 108

5.2 Determining Factors in Breastfeeding and Weaning Behavior.………. 113

5.3 The Biological Bases for Breastfeeding Duration and Weaning Age.... 119

5.4 Methods of Identifying Weaning Patterns in the Past.………………...125

5.5 Hard Tissue Strontium and the Inferences for Infant Nutrition.……… 132

5.6 Enamel Sr/Ca and Infant Nutrition at Lamanai.………………………. 136

6. MATERIALS AND METHODS…………………………………………………... 140

6.1 Analytical Technique.………………………………………………… 140

6.2 Technological and Methodological Challenges.……………………… 144

6.3 Materials and Methods.……………………………………………….. 152

6.4 Sample Preparation.…………………………………………………... 155

6.5 A Protocol for LA-ICP-MS Analyses of Human Dental Enamel.……. 158

6.6 LA-ICP-MS Observations.……………………………………………. 164

6.7 Laser Ablation Details for Lamanai Canines.………………………… 167

6.8 Data Analysis.………………………………………………………… 169

7. RESULTS OF ANALYSIS………………………………………………………... 177

7.1 Major Findings.……………………………………………………….. 177

7.2 The Lamanai Sr/Ca Pattern.…………………………………………... 180

7.3 The Sr/Ca Patterns of Lamanai Cohorts.……………………………… 190

7.4 Sr/Ca Patterns among Lamanai Individuals.………………………….. 212

7.5 The Nature of Enamel Sr/Ca Change in Lamanai Individuals.………. 224

7.6 Determination of Dietary Sr/Ca from Enamel Sr/Ca.………………… 244

xi

8. DISCUSSION……………………………………………………………………… 252

8.1 The Implications of Maize Processing for Dietary Reconstruction…... 253

8.2 Sr/Ca Behavior in Lamanai Permanent Canine Enamel.……………... 264

8.3 The Nature of Ancient Maya Health and Nutrition at Contact.………. 268

8.4 Implications of Infant Weaning Behavior for Ancient Maya Society... 281

8.5 The Comparative Hard Tissue Strontium Data.………………………. 286

8.6 Recommendations for Future Research.……………………………… 294

9. CONCLUDING REMARKS.…………………………………………………….... 298

APPENDICES

A. DENTAL HEALTH OF LAMANAI CANINES…………………………………. 305

B. ABLATION DETAILS FOR LAMANAI CANINES.……………………………. 327

C. STATISTICAL RESULTS………………………………………………………... 336

BIBLIOGRAPHY.………………………………………………………………...…… 345

xii

LIST OF TABLES

Page

2.1 Lamanai chronology.……………………………………………………... 11

3.1 Concentrations of major components of human dental enamel

excluding water and organic material.………………………………….… 59

3.2 Range of element concentrations in human dental enamel.…………….... 59

4.1 Average Sr content of various foods in order of relative abundance,

with some traditional Maya foods italicized.……………………………... 73

4.2 Mean Sr/Ca values for common Maya animal and plant foods

from the Pasion region of Guatemala.………...………………………….. 76

4.3 Ranges of Sr and Zn content in mammalian bones..……………………... 78

5.1 Constituents of human milk.………………………………………….…. 109

5.2 Bone Sr/Ca changes from the Dor sample, Israel.………………….…… 134

5.3 Bone Sr/Ca changes from the Schleswig sample, Germany.………….… 135

6.1 Sample Breakdown.……………………………………………………... 154

6.2 LA-ICP-MS Operating Parameters.………………………..………….… 160

7.1 Summary of mean 86

Sr/43

Ca for 0.25 year intervals.……………………. 182

7.2 Results of ANOVA comparing Postclassic and Historical individuals..... 184

7.3 Mean 86

Sr/43

Ca ratios for intervals between 0.5 and 5.5 years of age…... 185

7.4 Mean total Sr/Ca data (x10-3

) for Postclassic and Historical cohorts.…... 187

7.5 Results of Single Factor ANOVA (two-tailed) comparing Postclassic

Children and Adults.…………………………………………………….. 191

7.6 Results of Single Factor ANOVA (two-tailed) comparing Postclassic

Females and Males.…………………………………………………….... 192

7.7 Results of Single Factor ANOVA (two-tailed) comparing Historical

Children and Adults.…………………………………………………….. 193

xiii

7.8 Results of Single Factor ANOVA (two-tailed) comparing Historical

Females and Males.…………………………………………………….... 194

7.9 Average Sr/Ca values for 0.25 year intervals of Postclassic Children.….. 213

7.10 Average Sr/Ca values for 0.25 year intervals of Postclassic Females…... 214

7.11 Average Sr/Ca values for 0.25 year intervals of Postclassic Males.…….. 215

7.12 Average Sr/Ca values for 0.25 year intervals of Historical Children.…... 217

7.13 Average Sr/Ca values for 0.25 year intervals of Historical Females……. 218

7.14 Average Sr/Ca values for 0.25 year intervals of Historical Males.…….... 219

7.15 Average greatest increase in Sr/Ca from infancy to early childhood

(0.5-5.5 yrs) among Postclassic and Historical period individuals…….... 221

7.16 Age-related bone-diet observed ratios (ORbone-diet).……………………... 244

7.17 Enamel vs. Dietary Sr/Ca values for Lamanai cohorts at various ages…. 245

8.1 Relative Sr and Ca data for Lamanai bone and soil samples.………….... 257

8.2 Mean bone and soil Sr/Ca of Pasion Maya sites in Guatemala…………. 258

8.3 Comparative age-related mean Sr/Ca (x 10-3

) values from various

clinical and paleodietary investigations.……………………………….... 287

A.1 Regression formulae for calculation of timing of enamel defect

formation in Lamanai canines.……………………………………......…. 314

A.2 Average ages of enamel defect formation in the Lamanai sample....….... 318

A.3 Dental health details for Lamanai canines.………………………...……. 320

B.1 Ablation details for Postclassic Lamanai maxillary canines.…...…..….... 328

B.2 Ablation details for Postclassic Lamanai mandibular canines.…….…..... 330

B.3 Ablation details for Historical Lamanai maxillary canines……………... 332

B.4 Ablation details for Historical Lamanai mandibular canines.………….... 334

xiv

C.1 Results of Single Factor ANOVAs comparing total Sr/Ca increase

between Postclassic children and adults………………………………… 336


between Postclassic females and males…………………………….…… 336


between Historical children and adults………………………………...... 336


between Historical females and males………………………………....... 337


between Postclassic and Historical children………………………....….. 337


between Postclassic and Historical females…………………………....... 337


between Postclassic and Historical males…………………………......… 337

C.8 Results of Single Factor ANOVAs comparing Postclassic children

and adults.……………….……………………………………………..... 338

C.9 Results of Single Factor ANOVAs comparing Postclassic females

and males.……………………………………...……………..………….. 339

C.10 Results of Single Factor ANOVAs comparing Historical children

and adults.…………………………………………………………..….... 340

C.11 Results of Single Factor ANOVAs comparing Historical females

and males.………………………………………………...…………….... 341

C.12 Results of Single Factor ANOVAs comparing Postclassic

and Historical children.………………………………………………….. 342


and Historical females.…………………………………………………... 343


and Historical males.……………………………………………...……... 344

xv

LIST OF FIGURES

Page

2.1 Map of Belize showing the location of Lamanai.………………………… 10

2.2 Drawing of Structure N10-2.……………………………………………... 20

2.3 Map illustrating the southeastern Maya frontier,

with provinces and sites indicated.………………….……………………. 22

2.4 Remains of the second Spanish church at Lamanai.……………………… 24

3.1 Cross-section of human tooth, with major anatomical features indicated... 50

3.2 Three-dimensional chemical configuration of hydroxyapatite.………..…. 51

5.1 Proposed model of Sr/Ca behavior during infancy and early childhood... 137

6.1 Tooth cross-section indicating correlation of laser ablation

position, development age and enamel Sr/Ca intensity ratio…..………... 142

6.2 Position of laser ablation trenches along secondary canine crown.……... 158

6.3 Schematic of instrumentation used in LA-ICP-MS.…………………….. 161

6.4 Example of LA-ICP-MS recording sheet used in this analysis.………… 162

6.5 Graph illustrating distinct patterns in Sr/Ca during LA-ICP-MS.………. 165

6.6 Photograph of ablated tooth section and micrometer scale.……………... 167

6.7 Graphical comparison of different Sr/Ca isotope ratios in enamel.……... 173

6.8 Adjusted comparison of different Sr/Ca isotope ratios.…………………. 174

7.1 Standard Error graph of mean 86

Sr/43

Ca for all Lamanai individuals.…... 181

7.2 Standard Error graph of mean Sr/Ca for Postclassic

and Historical individuals.………………………………………………. 183

7.3 Scatter plot distributions of total Sr/Ca for Lamanai cohorts.…………... 188

7.4 Sr/Ca patterns of Lamanai cohorts.……………………………………… 190

7.5 Average Sr/Ca for Postclassic and Historical individuals.……………… 196

xvi

7.6 Comparison of total Historical sample with Postclassic adults.………… 197

7.7 Comparison of Postclassic and Historical cohorts.……………………… 200

7.8 Comparison of Postclassic Children and Adults.…..……………………. 202

7.9 Comparison of Postclassic Females and Males.………………………… 204

7.10 Comparison of Historical Children and Adults.………………………… 206

7.11 Comparison of Historical Females and Males.………………………….. 207

7.12 Comparison of Postclassic and Historical Children.…………………….. 208

7.13 Comparison of Postclassic and Historical Females.…………………….. 209

7.14 Comparison of Postclassic and Historical Males.……………………….. 211

7.15 Graph of Sr/Ca change among Postclassic children.……………………. 213

7.16 Graph of Sr/Ca change among Postclassic females.…………………….. 216

7.17 Graph of Sr/Ca change among Postclassic males.………………………. 216

7.18 Graph of Sr/Ca change among Historical children.……………………... 217

7.19 Graph of Sr/Ca change among Historical females.……………………… 220

7.20 Graph of Sr/Ca change among Historical males.………………………... 220

7.21 Distribution of peak Sr/Ca values per age interval.……………………... 222

7.22 Graph illustrating Postclassic individuals

with a general increase in Sr/Ca over time.……………………………... 225

7.23 Graph illustrating Historical individuals

with a general increase in Sr/Ca over time.……………………………... 226


with fluctuations in Sr/Ca over time.……………………………………. 230


with fluctuations in Sr/Ca over time.……………………………………. 231

xvii


with a delayed increase in Sr/Ca over time.……………………………... 237


with a delayed increase in Sr/Ca over time.……………………………... 238

7.28 Histogram of age of significant Sr/Ca change in “delayed” individuals... 240

7.29 Graph illustrating Lamanai individuals with stable Sr/Ca over time.…… 242

7.30 Comparison of enamel Sr/Ca and dietary Sr/Ca in Lamanai cohorts.…... 246

A.1 Standards of enamel hypoplasia severity....……………………………... 310

A.2 Distribution of defect timings in Lamanai maxillary canines....………… 317

A.3 Distribution of defect timings in Lamanai mandibular canines....………. 317

1

CHAPTER 1

INTRODUCTION TO RESEARCH

1.1 Introduction

The dietary and nutritional status of people in the past can be inferred by numerous

bone and dental indicators. These indicators can be grouped into three levels of analysis,

namely surface manifestations of disease or undernutrition, microscopic or histological

features, and studies of the chemical composition of tissues.

With regard to chemical make-up, numerous attempts have been made to assess the

relationship between what is consumed during life with consequent hard tissue

composition. Significantly, the overwhelming majority of these investigations have

focused on the isotopic and elemental chemistry of bone for dietary inferences.

Hard tissue chemical analysis is based on the fundamental principle that different

food categories have distinct elemental and isotopic compositions and that these

differences are reflected in the tissues of their consumers. Thus, hard tissue chemical

analysis provides a direct reflection of ancient subsistence (the meal), unlike the indirect

inferences from faunal and floral data and material evidence associated with food

processing (the menu).

Quantitative and qualitative methods of dietary reconstruction, such as those based on

faunal and floral data, are subject to preservation and often misrepresent consumption

proportions. Such data, in addition to dental microwear, stature and skeletal pathologies

indicative of health and nutrition, discloses only relatively broad inferences about diet.

(Note, while dietary status refers to the sum of all foods ingested, regardless of nutrient

2

value, nutritional status, refers to the state of balance between diet, nutrient intake and

functional capacity.)

For the purposes of paleodietary reconstruction, hard tissue analysis encompasses

assessments of elemental composition and stable isotopes, which reflect those of ingested

food types. This approach is based on studies that linked animal feeding habits with

variations in bone chemistry and isotopic composition (DeNiro and Epstein 1978, 1981).

Specifically, the application of chemical methods to reconstruct ancient diet from hard

tissues is built on the pioneering work of Brown (1973) and Gilbert (1975), followed by

DeNiro and Epstein (1978), van der Merwe and Vogel (1978), Lambert and colleagues

(1979), and Schoeninger (1979).

Importantly, it should be stressed that diet is only one of many variables that affect

bone composition. Variables such as individual metabolism and digestion, which vary

with food types and meal conditions; meal preparation; unequal absorption of nutrients

by the body; and the role of other substances in the diet on total elemental absorption

(e.g., phytates in maize) all contribute to the expressed hard tissue chemistry of an

individual.

Hard tissue chemical composition is not static during life and can be distinct between

bones and teeth. In this regard, dental enamel only reflects chemistry during its

calcification, since the mineral phase, or hydroxyapatite, of enamel is essentially inert

once formed, while living bone continuously remodels at a rate of approximately 2-4%

calcium turnover per annum (Avioli 1988), or ten years for total replacement (Bumsted

1985: 544). Thus, bone potentially provides a chemical record of approximately the last

ten years of life, while teeth (enamel) record varying periods between in utero

3

development to approximately 18-21 years of age, the entire period of deciduous and

permanent tooth crown formation.

Hard tissue elemental composition can be used to distinguish diet because they vary

in abundance in the environment. Prominent elements generally associated with animals

(and animal protein) include zinc, copper, molybdenum and selenium, while common

elements in plant material include barium, strontium, magnesium, manganese, cobalt,

nickel and vanadium (see Gilbert and Mielke 1985; Price 1989; Sandford 1993).

Additionally, because of the multi-elemental nature of hard tissue chemical studies, the

relationships between elements can also be used to indicate diet. For example, relatively

high levels of zinc, but low levels of strontium and magnesium can distinguish a diet rich

in animal protein, while high values for manganese, magnesium and strontium suggest

heavy reliance on plant foods.

Subsequently, the potentials of bone chemical analysis for dietary reconstruction have

been widely adopted. Utilizing bone elemental and isotopic composition, various studies

have examined the contribution of plants versus animals to human diet (Schoeninger

1979; Sillen and Kavanagh 1982); marine versus terrestrial components of diet (Ambrose

1991; Burton and Price 1990; Chisholm et al. 1982; Connor and Slaughter 1984; Nelson

et al. 1983; Schoeninger et al. 1983; Schoeninger and DeNiro 1984; Sealy and Sillen

1988); the transformation from hunting and gathering to agriculture (Schoeninger 1982;

Sillen 1981); infant nutrition and weaning (Sillen and Smith 1984) (see Chapter Five);

and the exploitation of certain species of plants such as maize (Bender et al. 1981;

Katzenberg et al. 1993; Lynott et al. 1986; Norr 1981; Reed 1994; Schoeninger 1979;

4

Schoeninger et al. 1990; Vogel and van der Merwe 1977; White 1986; White et al. 1993,

1994; Wright 1994, 1997, 1999; among others).

To date, the analysis of hard tissue (bone) composition to infer childhood nutrition

has been clouded by challenges in pinpointing precise periods of early development. In

particular, it is not fully understood how bone chemistry reflects diet and nutrition at

different stages of development. Related to this is the problem of not knowing the time

delay between ingestion of foodstuffs and their chemical incorporation in hard tissues.

Utilization of bone material to infer nutrition is also hampered by the organic nature

of bone, which renders it highly susceptible to post-depositional contamination and

deterioration (see Ambrose 1991; Armelagos et al. 1989; Chisholm 1989; DeNiro 1985;

Pate and Hutton 1988; Lambert et al. 1985; Price 1989b; Price et al. 1992; Sandford

1993; Sillen and Sealy 1995; Sillen et al. 1989, among others). Diagenesis is the sum of

all physical, chemical and biological processes that occur in the postmortem depositional

environment to alter hard tissue composition.

Furthermore, conventional techniques adopted until very recently are characterized by

complete dissolution of hard tissues for chemical analysis. Chemical signatures either

reflect the combined composition of hard tissues in the sample, which may include post-

mortem contaminants, or they reflect very specific locations of bone that cannot be

“aged” accurately due to bone turnover. Elemental and isotopic analyses of dissolved

samples mean that archaeological human remains are lost forever.

Fortunately, these shortcomings can be overcome by analyzing the chemical

composition of teeth by laser ablation-inductively coupled plasma-mass spectrometry

(LA-ICP-MS). LA-ICP-MS is a method of multielement analysis that can sample precise

5

regions of hard tissues to infer dietary intake (see Chapter Six). In this study, such an

application is focused on enamel, which is significantly more inorganic (97-98%) and

resistant to diagenesis than dentine, cementum and bone (see Chapter Three).

The appearance and composition of teeth reflect the health and dietary status of

individuals during childhood, the period when teeth are formed. Teeth are an ideal

analytical material because they are incremental biological structures that are not

significantly remodeled after formation, unlike bone, which undergoes constant turnover.

Since they sequentially calcify at a known rate, they are invaluable to dietary studies that

seek to associate dietary intake, in the form of tissue chemistry (and intra-tooth

variation), with developmental age. Enamel, in particular, has an inherent permanent

“time axis” (Lee et al. 1999), which can be recognized microscopically as sequential

Striae of Retzius. Teeth are thus an indelible record of early development, providing

meaningful clues to a critical period of human adaptation.

Recognizing the attributes of dental material that make them ideal for chemical

methods of paleonutritional reconstruction, this study focuses on enamel elemental

composition to infer dietary behavior of young children in the past. Secondary canines

are used since they trace diet and nutrition of individuals from approximately birth to five

or six years of age, the period when such teeth develop. Specifically, this research

focuses on changes in diet during weaning, a key maturational event in human life history

that has consequences for future survival (see Chapter Five).

Chemical analysis of canine teeth will focus on the element strontium (Sr) and its

ratio to calcium (Ca) in enamel (see Chapter Four). The application of strontium to

paleodietary reconstruction is based on the element’s relative concentration in breast milk

6

and solid foods. As strontium abundance differs dramatically between breast milk (low)

and food (high), it is postulated that the process of exclusive breast milk intake to dietary

supplementation and weaning should be visible as a change in strontium, relative to

calcium (Sr/Ca) (see Chapter Five). The duration of breast milk intake, and the age at

which children are weaned, are significant predictors of future growth and development.

1.2 Cultural Context of the Investigation

All told, the teeth will be analyzed as biological testimony of the indigenous

experience during the early Spanish contact period in the Americas. Changes in

indigenous health from the 16th

century A.D. onward will be traced through the health

status of children. The health of children is a sensitive indicator of overall population

health (Goodman and Armelagos 1989) and, importantly, it is a reflection of a “group’s

ability to manage its social and physical environment” (Swedlund and Ball 1998: 195).

Dental remains from the ancient Maya site of Lamanai, northern Belize, will be

employed in this study (see Chapter Two). Lamanai is noteworthy in Maya prehistory

for its lengthy archaeological record. Culturally, health will be examined within the

historical context of Maya resistance and cultural syncretism at the site. Regarding

Lamanai, I will address the question: How is the unique nature of native resistance and

syncretism at this “frontier” post reflected in the health and nutritional status of its

inhabitants? In particular, did the political, economic and social conditions of

colonialism, in the midst of some indigenous autonomy, effect dietary and/or health

changes among Maya women and children, and can these changes be recognized in

childhood nutritional status?

7

Drawing from archaeological, osteological and ethnographic evidence, specific

concerns include: 1) Are there temporal distinctions in breastfeeding and dietary

supplementation between pre-colonial and historical periods? 2) Did Spanish control of

economic activities, i.e., demands for agricultural products and human labor, affect

household patterns and childhood nutrition? 3) Did this demand for increased labor

result in any changes in weanling diet or duration? 4) Is the heterogeneous nature of the

colonial mission population, including Maya “refugees” from other areas, reflected in

childhood diet and weaning patterns? 5) Are there distinctions in weaning age, duration

or diet that could be related to socioeconomic status or gender?

1.3 Theoretical Framework

In terms of a research paradigm, interpretations of the enamel chemistry are situated

in a biocultural anthropology framework, which is rooted in the materialism of political

economy. According to Goodman and Leatherman (1998: 19-20), five main tenets of

political economic theory form the foundations of biocultural anthropology:

1) Examining biological variation in terms of social relations (of power) through

which individuals gain access to basic resources and labor (production and

distribution); importance of social processes

2) Recognition of links between the local and the global (macro-micro

interconnections)

3) History and historical contingency are critical to understanding the direction of

social change and the biological consequences of change

4) Humans are active agents in constructing their environments

5) Ideology and knowledge, of both subjects and researchers, are essential to

understanding human action

8

These concepts frame the objectives of this investigation. Understanding the status of

indigenous health and nutrition at the nexus of Maya-Spanish contact demands an

integrated and critical biocultural approach. It recognizes that children, as the most

vulnerable members of society, are the most impacted by the interactions between

biology, culture and ecology. Thus, beyond infant diet, this investigation considers the

roles of women in Maya society; childcare practices and individual decisions regarding

infant nutrition; access to food resources; disease ecology and the cultural, political and

economic factors that constrain or determine the weaning process.

Like recent dental research by Wright and Schwarcz (1998), this study adds to the

immense potentials of teeth for understanding the health and nutrition of past

populations. Methodologically, the application of LA-ICP-MS technology to this study

offers a minimally invasive means of (micro)sampling and multielement profiling that

takes advantage of the developmental databanks that are teeth. Thus, the structural

integrity of teeth is preserved at the same time a chronological profile of hard tissue

chemistry is detailed (see Chapter Six). It is an ideal method to capture the complex

history of a critical developmental period in the human life cycle.

As such, the present study represents an evolution of paleonutritional research in two

respects: it employs new, non-destructive, micro sampling technology in the form of

Laser Ablation- Inductively Coupled Plasma-Mass Spectrometry (LA-ICP-MS) to

analyze the nature of intra-tooth variation in the chemical composition of dental hard

tissues to trace dietary transitions and life history during early childhood.

9

CHAPTER 2

THE MAYA OF LAMANAI, BELIZE

2.1 Lamanai Research History

The present application of LA-ICP-MS analysis to paleonutrition utilizes dental

remains from the ancient Maya site of Lamanai, northern Belize (Figure 2.1). Lamanai is

the archaeological focus of research because of its unique continuity from prehistoric to

historical times and the interdisciplinary nature of long-term investigations.

Lamanai, or Indian Church as it was known in Belize since the 19th

century, and

which roughly means “submerged crocodile” in Maya, was excavated under the direction

of Drs. David M. Pendergast and Elizabeth Graham of the Royal Ontario Museum

primarily between 1974 and 1986.

Extensive research includes more than 25 years of ongoing archaeological excavation

and analysis (Pendergast and Graham, various; Loten 1985; Powis 2001); osteological

analyses of disease, dental morphology and bone chemistry (Coyston et al. 1999;

Helmuth and Pendergast 1989; Lang 1990; White 1986, 1988, 1997; White and Schwarcz

1989; White et al., 1994; Wright 1990); zooarchaeological reconstruction of the faunal

assemblage (Emery 1990, 1999; Lovisek, R.O.M.); botanical studies (Lambert and

Arnason 1978, 1979); and investigations of ethnohistorical records (Graham et al. 1989;

Jones 1989).

10

Figure 2.1 Map of Belize showing the location of Lamanai

(from Pendergast 1981: Fig. 1)

11

Archaeological work has resumed since 1997 by the principal directors heading the

Lamanai Archaeological Project, as well as site development carried out by the Tourism

Development Project since 2001 (Ministry of Tourism and Youth, Government of

Belize). Throughout, particular attention has been directed toward site restoration,

consolidation, and its development as a national park for tourism.

From these investigations, Lamanai emerges as an important ceremonial, trade and

administrative center in the Maya Lowlands during much of the Classic (A.D. 300-1000)

and Postclassic (A.D. 1000-1520) periods. It is noteworthy for having one of the longest

continuous settlements in the Lowlands, spanning from 1500 B.C. (or earlier) to A.D.

1675, and a dynamic archaeological record (Graham et al. 1989; Pendergast 1981, 1986,

1991a,b, 1992, 1993). The following chronology outlines the various cultural phases for

Lamanai.

Table 2.1 Lamanai chronology

Time Period Dates

Preclassic

Early 2500-1250 B.C.

Middle 1250-400 B.C.

Late 400 B.C.-A.D. 250

Classic

Early A.D. 250-400

Middle A.D. 400-650

Late A.D. 650-900

Terminal A.D. 900-1000

Postclassic

Early A.D. 1000-1100

Middle A.D. 1100-1400

Late A.D. 1400-1544

Historical A.D. 1544-1670

12

2.2 Environmental Setting

The site of Lamanai lies within the north-central coastal plain region of Belize,

Central America (Figure 2.1). It is situated at approximately 170 46’N latitude and 880

39’W longitude, while the country of Belize as a whole is located between the latitudes of

150 N and 180 N, which puts it on the fringes of the tropical (0-150 N) and subtropical

(20-300 N) latitudinal belts (Smith and Panton 1986: 48). Presently, the site is located in

the southern half of the Orange Walk District of Belize, approximately 70 km from the

Caribbean coast, within the 385 hectare Lamanai Archaeological Reserve.

The northern lowlands of Belize resemble the geology and landscape of much of the

Yucatan peninsula, with gently sloping limestone hills, calcium carbonate rich soils, and

level plains mainly under 100 meters above sea level. In the Lamanai Archaeological

Reserve, elevation averages around 30 meters above sea level. Rivers in the region are

generally slow-flowing because of the lack of gradient and often pass through badly

drained swampland (Furley and Crosbie 1976).

Lamanai falls within Thornthwaite’s (1948) Subtropical zone, or the Dry Tropical

climate zone according to the classification system of Wright and colleagues (1959: Figs.

II, VIII). The Dry Tropical zone, which encompasses all of northern Belize and most of

central Belize, has a mean annual temperature of more than 240C (750F). It generally

receives from 1500-1750 mm of rainfall per year, but not more than 2000 mm (Wright et

al. 1959).

The period between January and May has relatively dry weather, which is

characterized by less than 100 mm (4 inches) of rainfall (Furley and Crosbie 1976: 12).

Generally, the wet season occurs between June and December, but the region is prone to

13

radical fluctuations in rainfall from year to year. Thus, some years experience no real dry

season, while extended dry seasons often follow. Presently, the usual planting season for

maize, a primary staple of ancient and contemporary Maya and Latin American diets, is

April to May (Furley and Crosbie 1976).

Cyclones, in the form of tropical depressions, storms, or hurricanes, frequently

develop from the Caribbean Sea, and can drastically affect typical weather patterns

throughout Belize. Tropical storms and hurricanes are most active over Belize between

August and October, with peak occurrences during the month of September (Gibson

1983), but their number and regularity vary from year to year. Severe hurricane

conditions have caused widespread coastal flooding and alteration of portions of the coast

and offshore cays (e.g., Hurricane Hattie, 1961). While such destructive events cannot

currently be extrapolated from prehistoric contexts, weather records indicate that Belize

has experienced about three hurricane episodes, on average, every 10 years (Furley and

Crosbie 1976).

Regarding vegetation, the Lamanai area consists of several distinct types: broadleaf

forest, high bush, cohune ridge, swamp broadleaf forest (swamp [bajo] and riparian

forest), pine savanna, grasses, shrubs, tropical forest and alluvial shoreline (Lambert and

Arnason 1978; White 1986). Past and present evidence indicate that the region is rich in

tree species, some of which include mahogany, ceiba, sapodilla, breadnut, allspice,

chicle, cherry, cohune palm, cedar, gumbolimbo, copal, strangler fig, bay leaf palm, and

poisonwood, among many others (Hartshorn et al. 1984; Lambert and Arnason 1978;

Pohl 1990; Turner and Harrison 1983).

14

From an economic standpoint, approximately one third of the available tree species in

northern Belize provide fruit or leafy components that are suitable for human

consumption. Some include sapote, breadnut/ramon nut, allspice, cohune, strangler fig,

wild papaya, bay cedar, hogplum, guanacaste, Piper, and the pork-and-doughboy palm (J.

Eckenwalder, personal communication, 1996; Standley 1961).

The majority of plants around Lamanai do not contain edible components, but many

of these species are, and were, important sources of lumber, as well as ritual (copal) and

medicinal products (e.g., Acacia, bay leaf palm, bookut, cedar, copal, dogwood, Ficus,

gumbolimbo, mayflower, Mimosa, papaya, Piper, and the trumpet tree [see Roys 1931]).

2.3 The Nature of Human Settlement at Lamanai

Surveys at Lamanai between 1974-1976 located 718 structures (which now exceeds

720) within a 4.5 km2 area, or a settlement density of approximately 160 structures per

km2 (Pendergast 1981: 32). Compared to the rate of 367 structures per km

2 of habitable

terrain at Altun Ha (Pendergast 1979), and the 810 structures per km2 at wall-enclosed

Mayapan (Jones 1952), which represents the high end of Maya settlement density,

Lamanai inhabitants enjoyed relatively pleasant living conditions.

Numerous features can be recognized as having attracted settlers to Lamanai: fresh

water from the New River lagoon and New River, proximity to the Caribbean Sea, and

diverse food and trade resources. As stated above, the area is rich in vegetation diversity,

but numerous aquatic ecosystems are also close at hand: lagoon, river, estuary, coastal

reef and sea. As White (1988: 3) states, the ecological and resource diversity at Lamanai

makes it “an environmental microcosm for the entire Maya Lowlands”.

15

Archaeological evidence suggests that the site was inhabited by at least 1500 B.C.,

which is when pollen cores indicate the cultivation of maize (Pendergast, personal

communication to White, 1988). Such agriculture was achieved by several methods,

namely slash-and-burn milpa, raised fields and other irrigation techniques. Raised fields

have been identified in the northern limit of the site, but their date of origin is

questionable (Lambert et al. 1984). According to Lambert and Arnason (1979), the

production potential of the Lamanai area for maize far exceeded even the highest

population estimates, with the adoption of variable agricultural practices preventing the

likelihood of soil exhaustion (Lambert 1985).

Unlike most sites in the southern Lowlands, including important centers nearby (e.g.,

Altun Ha), Lamanai survived the Maya “Collapse” of the ninth century A.D., as indicated

by archaeological evidence of political, economic and demographic stability (Loten 1985;

Pendergast 1981, 1986, 1991a, 1992). In particular, architectural and material evidence

suggest continuity of Classic period ideology, religious belief and practices. This

stability is atypical for the Maya Lowlands at this time. While many centers were

abandoned during the Terminal Classic (AD 900-1000), after experiencing socio-

political, economic and ideological upheaval, Lamanai witnessed sustained construction

of monumental public and ceremonial architecture, as well as residential structures.

The reasons for this stability at Lamanai are numerous and interrelated and include:

1) the lakeside setting of the site, which provided numerous resources; 2) its access to the

New River, which was a busy route for trade and contact with many regions of

Mesoamerica; 3) their long-standing participation in trading networks; and 4) the moral

fortitude and personality of community leaders (Pendergast 1981, 1986, 1991a, 1992).

16

A principle factor for Lamanai’s endurance was its setting. Located on the western

shore of the New (or Dzuluinicob) River Lagoon, just south of its northern juncture with

the New River, Lamanai is situated at the head of a major riverine trade route. Presently,

the New River Lagoon is the largest body of open water in Belize.

Owing to its lakeside setting, settlement at Lamanai took on a “decidedly non-

standard settlement pattern, in which the usual arrangement of one or more ceremonial

precinct plaza groups, surrounded by zones of residential and other small structures, gives

way to a sort of massive strip development with not a single ceremonial grouping

resembling those generally encountered elsewhere” (Pendergast 1981: 32). This unusual

pattern is distinct from many lowland Maya centers, including nearby Altun Ha and San

Jose, but it served to control access of the upper reaches of the New River’s headwaters

(Pendergast 1981).

Beyond the diverse food resources of the lagoon and river (see below), Lamanai’s

location was probably more important as a means of communication with other parts of

Mesoamerica. This route connected the Northern Maya Lowlands, the Caribbean coast,

the Southern Lowland interior and southern regions of Mesoamerica to the inhabitants of

Lamanai. For instance, artifact and architectural styles and materials indicate that

Lamanai had a long history of extensive contact with foreigners from western and central

Mexico (Oaxaca), the Guatemalan highlands, the Peten, Yucatan, Honduras and Lower

Central America (Pendergast 1981, 1986, 1991a, 1992). Overall, the quantity and variety

of Late Classic and Postclassic trade goods reflect the site’s prosperity and status among

traders and merchants throughout Mesoamerica.

17

Importantly, during the Postclassic and Historical periods, the New River was the

conduit through which human migration, as well as the trade of materials and ideas,

flowed into territory controlled by Tipu (see Figure 2.3). This site in western Belize,

located on the Macal River near its junction with the Mopan River, was the political

center of the Dzuluinicob province and was a major site of native resistance during

colonial times.

Furthermore, Lamanai’s situation on the New River provided direct access to the

Caribbean Sea. Other than marine dietary resources, which were restricted to elites, the

sea also provided the inhabitants of Lamanai with a rich and varied material culture.

Based on the faunal evidence, numerous vertebrate and molluscan resources were

exploited by the Lamanai Maya throughout its occupation (Emery 1990, 1999). As at

nearby Altun Ha, marine resources such as bony fish, shark, stingray, manatee and shell

species (Spondylus, Strombus and Oliva, among many others) were available to higher

status inhabitants, and they were also important commodities involved in long-distance

trade to inland sites (Pendergast 1979).

Participation in far-reaching trade networks via the New River ensured that Lamanai

elites prospered, and this is clearly evident in the abundance of elaborate public

architecture at the site, including a 33 meter high temple pyramid as early as the Late

Preclassic (100 B.C.), and numerous equally monumental structures thereafter (see

Pendergast 1981, 1986, 1991a, 1992). Artifactual and iconographic evidence further

establish Lamanai as an important political, economic and ceremonial Lowland Maya

center for most of its history.

18

2.4 Food Resources

The diverse ecological setting of Lamanai also meant that its inhabitants had access to

significantly more varied dietary resources than were available at sites further inland.

Local resources were exploited from jungle, pine ridge, lacustrine, riverine and marine

ecosystems. The lagoon and river provided abundant resources such as thirty-one species

of freshwater fish, turtle and other water-based animals such as birds, manatee, eel,

shellfish, and snails (see White 1986: Table 1). Other local fauna include important food

resources such as deer, peccary, dog and turkey, in addition to rabbit, armadillo, large

rodents such as paca and agouti, opossum, tapir, pheasant, monkey and squirrel, among

others (Emery 1990, 1999; Hellmuth 1977; Shaw 1991; White 1986; Wing and Scudder

1991).

These resources supplemented a diet based on locally grown staples such as maize

(Zea mays), beans (Phaseolus sp.) and squash (Cucurbita sp.), which were probably

grown in nearby raised fields (Lambert and Arnason 1978, 1979; Pendergast 1991a).

Archaeobotanical evidence indicates that maize was probably produced at the level of

self-sufficiency during the Postclassic (Pendergast 1986).

A wide variety of other domesticated and wild plant foods were also available,

including chile peppers, sweet peppers, tomato, various root crops (manioc, jicama, sweet

potato) and tree crops such as avocado, cacao, cashew, coconut, fig, mango, mamey

apple, papaya, ramon, palm and guava (see Hellmuth 1977; Lentz 1999; Miksicek et al.

1991; Pohl 1990; Turner and Miksicek 1984; White 1986, 1999, among others). Cotton

and other fibers were also locally grown.

19

Ironically, despite ecological diversity, zooarchaeological data suggest that consumed

food diversity diminished significantly during the Late Postclassic and continued in this

way into the Historical period. At these times, Lamanai Maya relied increasingly on

cultivated foods and a small number of animal species, particularly riverine ones, to the

exclusion of other resources. Exploited animal resources included turtle, fish, birds,

turkey, and curassow (Emery 1990, 1999). This was supplemented with a small amount

of imported marine foodstuffs (primarily among elites), as well as imported salt

(Pendergast 1986).

2.5 The Postclassic and Historical Periods at Lamanai

In the Postclassic period (A.D. 1000-1520), Lamanai Maya shifted settlement toward

the southern limit of the Classic period site core, which was eventually abandoned

(Pendergast 1986, 1991a). The Postclassic sample of 115 burials consists of individuals

interred in Structure N10-2, a predominantly Middle Postclassic ceremonial structure in

the Postclassic central precinct, and Structure N10-4, a Middle to Late Postclassic

structure adjacent to N10-2. Male and female adults are equally represented and

subadults are likewise interred in the same context.

Based on burial context, construction and grave offerings, Structure N10-2

individuals are considered high in socioeconomic status, and because of its adjacent

proximity, Structure N10-4 burials are also likely privileged (Pendergast 1981). Hard

tissue chemical composition, reflecting dietary intake, supports the lack of status (or sex)

differentiation in the Postclassic sample (Coyston et al. 1999; White 1986). Skeletal

evidence suggests that Postclassic individuals were generally healthy (White 1986).

20

The largest number of Postclassic burials derives from Structure N10-2, which,

alongside N10-1, was the ceremonial focal point for the Terminal Classic and Postclassic

community until the 15th

or early 16th

century (Pendergast 1986). At least fifty

Postclassic burials were excavated from Str. N10-2 (see Figure 2.2).

Figure 2.2 Drawing of Structure N10-2 (Pendergast 1981: Fig. 17)

Structure N10-4 was a Classic period structure that continued in use into the

Postclassic as a burial mound, with two or more small structures atop. Forty-seven

Postclassic burials, all derived from a single construction period, were interred overlying

the remains of an Early Classic structure (Pendergast 1981). The majority of these

remains are contemporaneous with the later remains of N10-2, dating to the late 15th

to

early 16th

century A.D.

While the entire Postclassic sample is generally “privileged” in socioeconomic status

(i.e., greater access to resources and social power), as inferred by interment context and

burial assemblage, several individuals are particularly notable, namely N10-2/9, N10-

2/20 and N10-4/46 (Pendergast 1981, 1992). The wealth of burial artifacts, including

copper and gold sheet objects, distinguishes these male individuals as nobles or

21

community leaders. (Teeth from Individuals N10-2/20 and N10-4/46 are included in the

present analysis.) According to Pendergast (1991b), the primary individual of burial

N10-4/46 is probably the most important in the Postclassic group based on two accounts:

1) its very late date, of the early 16th

century (post A.D. 1525), is from a period which is

little evidenced elsewhere at the site; and 2) it is possibly the last pre-Hispanic ruler of

Lamanai.

The Historical period (AD 1544-1670) at Lamanai is notable for a Spanish presence

that interfered with aspects of Maya lifeways amidst preservation of some cultural

autonomy. Rich archaeological and ethnohistorical documentation indicate that the site

was an important frontier center of Maya resistance during the Historical period, with

components of indigenous culture existing side-by-side with Christian churches and

ideology (Jones 1989; Graham et al. 1989; Pendergast 1991b, 1993).

Unfortunately, notwithstanding historical accounts by Landa (1566), Lizana (1633),

Lopez de Cogolludo (1654, 1688), and Oviedo (1535-1547), there is difficulty detailing

all aspects of Maya life at the time of contact, due to both Spanish ignorance of

indigenous material culture, and the intentional concealment of Maya activity from

Spanish writers (Jones 1989).

As a result, reconstructing indigenous culture at that time has relied on integrating

ethnographic and historical accounts with the archaeological record. This approach is

problematic at times, with discrepancies occurring between the two “truths” (see Jones

1989; Rogers and Wilson 1993). Nevertheless, combining these complementary modes

of cultural reconstruction has been fruitful for the southeastern Maya frontier, due to

invaluable ethnohistorical documents and abundant archaeological data for the sites of

22

Figure 2.3 Map illustrating the southeastern Maya frontier, with provinces and sites

indicated (adapted from Jones 1989)

23

Lamanai and Tipu (see Figure 2.3) (Jones 1989, 1998; Jones et al. 1986; Graham 1991;

Graham et al. 1989; Pendergast 1981, 1986, 1991a, b, 1993).

Notably, however, while Tipu is well documented in historical sources, there are

scant written records of Lamanai (Jones 1989). As stated by Jones (1989), this fact is

perplexing as Lamanai has the remains of two ramada churches (structure with a pole

and palm-thatch covered nave), one more substantial than at Tipu, numerous Christian

Maya burials and domestic architecture.

The few historical references that do exist indicate that the Spanish first visited

Lamanai, which was usually spelled Lamanay, shortly after 1544 (Jones 1989;

Pendergast 1992). At this time, it was established as an encomienda (royal grant to

Spaniards for the right of tribute from native populations, and usually composed of one or

more towns) following the 1543-1544 conquest of the region (Jones 1989). Up until

then, at least the southern third of the Postclassic settlement was still functioning as a

community, alongside a satellite community near the northern boundary, but the ancient

ceremonial core remained abandoned (Pendergast 1981, 1986).

The first Christian church at Lamanai (Structure N12-11) was erected around A.D.

1545-1550, 0.75 km south of the Postclassic ceremonial center, for the relocated scattered

settlement. It was utilized until almost the end of the 16th

century (Pendergast 1991b).

Following the practice common throughout the colonized Americas, it was built over an

earlier indigenous ceremonial structure. At Lamanai, it entailed the destruction of most

of a small, fresco-decorated temple dating to the 15th

century for an earthen platform that

supported a masonry and perishable material structure. As succinctly stated by

Pendergast (1991b: 341), this structural superposition had “the eminently practical aim of

24

perpetuating precontact patterns of activity while supplanting one form of religious

practice with another”.

This original church was modest, with a nave measuring only 6 x 9 meters

(Pendergast 1991b: 342). It served a small local community that operated on the visita

(circuit-riding) system, which saw Spanish priests circulating among many different

parishes, aided by local Maya religious figures (Pendergast 1991b).

The second church was built around A.D. 1600, just north of the first church, and was

much larger than the original, with substantial masonry architecture (Graham et al. 1989)

(see Figure 2.4). Unlike the first church, architectural traits of this one were fully

European and resembled other churches in the Yucatan (Pendergast 1991b).

Figure 2.4 Remains of the second Spanish church at Lamanai

In 1637, Lamanai was listed as a reduccion town, or a compact community composed

of the forced resettlement of the native population from nearby villages, and its Maya

25

citizens paid tribute to Salamanca de Bacalar (Jones 1989). Based on tribute payment

records, a population of 72 people is suggested at this time (Archivo General de Indios,

Seville, in Jones 1989: 117, 310). By now considered a vacant encomienda made up of

“runaway Indians” from the Bacalar region, many of who were later reduced back to San

Juan Extramuros at Bacalar, it was known as a trouble-making community (Jones 1989).

The period between 1638 and 1677 was a notable period of resistance and rebellion in

the Lamanai and Tipu areas (Jones 1989). At this time, the Yucatan and southeast

periphery were especially turbulent, with increasing Maya migration to the frontiers of

Belize. Accompanying this were epidemic disease, successive famines, frontier

rebellions inspired by millennial prophecy, increasing piracy and foreign control of

logwood cutting and export, and repartimiento (forced advances of cash or goods in

return for native-produced foodstuffs, crafts or natural products) exploitation (Graham et

al. 1989; Jones 1989).

Based on ethnohistorical and archaeological evidence, it appears that unlike most pre-

Columbian Maya sites, Lamanai witnessed a dynamic Maya presence during colonial

times. As stated earlier, Lamanai’s continuity was primarily due to its geographic

location. Even during colonial times this fact ensured the Maya community’s survival.

At this time, Spanish administrative control in the Maya Lowlands was based at

Merida in the Yucatan, with regions south of Chetumal Bay practically unknown

frontiers. Even to natives of the north, the southern portion of the Maya Lowlands was

considered frontier territory and the land of foreigners. The New River in northern

Belize was often called Dzuluinicob in ancient times, meaning “foreign people” in Maya

(Lopez de Cogolludo, 1688 [5th

ed., 1971]), and the same term also applied to the region

26

south of the New River Lagoon in central and west-central Belize (Jones 1989). As a

frontier, numerous Maya communities existed along the New and Belize Rivers outside

the control of Spanish forces.

The southeastern provinces of the Maya “frontier” were a dynamic breeding ground

for both active resistance and cultural syncretism, and it was a transitional zone that

“connected the native world of the colonized Yucatan to the north with the genuinely

independent Maya world of the Itzas of the Peten” (Jones 1989: 123). Both people and

ideas were safely hidden here and, consequently, Spanish attempts to pacify these

provinces (e.g., establishment of the villa at Salamanca de Bacalar) were geared toward

monitoring indigenous resistance movements, potential rebellions and Maya runaways

from the north, rather than for the purposes of collecting tribute (Jones 1989).

Besides being in the Maya “frontier”, Lamanai was strategically placed midway along

a major riverine route between Bacalar, the important Spanish administrative center

located near Chetumal Bay that controlled the ancient province of Chetumal, and Tipu,

the political heart of the Dzuluinicob province (Graham et al. 1989; Jones 1989) (see

Figure 2.3). Tipu is located in a small valley in the foothills of the Maya Mountains and

was the last of a series of visita missions extending south-southwest from the villa of

Salamanca de Bacalar (located more than 200 km away by river and land) (Figure 2.3).

The Dzuluinicob province was composed of indigenous Yucatec Maya speakers and it

became the primary center of Maya resistance to colonial rule (Jones 1989).

Maintaining its pre-Columbian past, Lamanai acted as an important hub for trade and

communications during the 16th

and 17th

centuries (Graham et al. 1989; Pendergast

1991b, 1993). However, in contrast to the relative stability of Tipu, Lamanai, as a

27

reduction center for runaways from the Bacalar region, experienced more population flux

and instability (Graham et al. 1989; Jones 1989). Despite its proximity to the

administrative center of Bacalar though, which made it vulnerable to Spanish control,

native Maya material culture at Lamanai was well represented.

Architecturally, there was a noticeable change from a pre-Columbian tradition to

Spanish influenced masonry at Lamanai, albeit on a limited scale, but there was no

significant alteration to the pre-Hispanic settlement pattern, which was already restricted

by the lakeside location (Graham et al. 1989; Pendergast 1981, 1986, 1991a, b).

Compared to many other Spanish-controlled colonial centers, which generally exhibited

European town plans, the situation at Lamanai was unique and likely reflects Spanish

efforts to attract Maya refugees (Graham et al. 1989; Pendergast 1991b).

In terms of small-scale material culture it appears that there was also general

continuity of artifacts. To a limited extent, some types of European artifacts were

accepted, but the material culture of colonial period Maya remained surprisingly

traditional and significantly more numerous than Spanish imports. This is particularly

visible in ceramics and lithic tool production (Graham 1991; Graham et al. 1989;

Pendergast 1991b). In total, Spanish material culture was “never more than an overlay on

that of the Maya” (Graham et al. 1989: 1258).

The European imports that appear in the archaeological record at Lamanai most often

occur in burial contexts and they were most certainly material symbols of socio-economic

status (Graham et al. 1989). Historical documents suggest that gifts such as glass beads,

rosaries, axes, machetes, knives, needles, silver and glass earrings and necklaces were

given by priests to encourage religious conversion (Villagutierre Soto-Mayor 1983).

28

In response to religious proselytizing, which, in addition to the seizure of land and

resources, was the main goal of Spanish colonists, Maya groups throughout the Lowlands

and Highlands resisted. Other than material cultural stability, important insight into

various forms of community resistance can be drawn from ethnohistorical texts and

demographic records. Such evidence suggests that in response to heavy tribute and

taxation demands, cultural and religious persecution, economic constraints, brutality,

massacres, famine, and disease, many Maya protested Spanish hegemony by violent

protest and out-migration (Clendinnen 1987; Farriss 1984, 1993; Jones 1977, 1989, 1998;

Landa in Tozzer 1941; Restall 1997; Varner and Varner 1983).

Native resistance also came in the form of upholding cultural traditions, as well as

cultural syncretism with European customs. Language, a fundamental symbol of culture

and group identity, was an important mechanism through which colonial period Maya

resisted Spanish influence. Spanish terms were adopted, but the general rule was not to

borrow Spanish words if there was an equally appropriate Maya term (Farriss 1984). In

contexts involving discourse between Maya and Spanish, it was usually Yucatec Maya

that was employed, through the use of interpreters (Farriss 1984).

The minimal extent of Spanish language conversion during colonial times is at odds

with the enormous efforts undertaken to instill Christianity. This may be attributed to the

moral fortitude of Maya communities to maintain language above all else, as a clear

symbol of identity, but it was also due to the laxity of Spanish attempts to impart their

language (Archivo General de la Nacion, 1790-1805, in Farriss 1984).

On the other hand, Maya culture during the 16th

and 17th

centuries also reflects a great

deal of cultural syncretism with Spanish traditions, namely in the form of religious

29

acceptance. The main features of Maya/Christian religious syncretism include:

integration of the vast Maya pantheon with Christian saints (represented physically as

figurines or censers); adoption of Christian holy days such as Good Friday and Easter,

which were secondary in importance compared to the syncretic All Souls’ Day (“a

merger between the Catholic concept of restless souls in purgatory and Maya notions of

the afterlife” [Farriss 1984]); expression of sacred Christian imagery within native

contexts (e.g., crucifixes upon altars surrounded by offerings); and the incorporation of

copal incense, ritual balche drinks, offerings of maize, turkey and deer, pre-Columbian

songs, dances and traditional instruments with Christian rituals (Clendinnen 1987; Farriss

1984, 1993; Jones 1977, 1989, 1998; Miller and Farriss 1979; among others).

It is obvious in reading the historic accounts of Spanish priests, leaders and scribes

that despite efforts to Christianize native communities, and despite the appearance of

conversion to Christianity, there was an active preservation of traditional Maya religious

practices. Entradas and other passages through Maya communities frequently

encountered native “idols” in houses and temples, even practically “under the noses of

clerics”, and as a typical example, Juan Garzon (1568, cited in Jones 1989: 49) stated that

they found “so many idols that they couldn’t easily be counted”.

These “idols” were anthropomorphic and zoomorphic censers, whistles and figurines

that likely had multiple functions and various religious and non-religious significance.

They were commonly found in churches, caves, and shrines and recesses of Maya homes

(Jones 1989; Farriss 1984). At both Tipu and Lamanai, such pre-Columbian-style

effigies were found in refuse deposits and offerings in colonial period buildings,

testament to the fact that native religion was not entirely displaced by Christianity

30

(Graham 1991; Graham et al. 1989; Pendergast 1991). In one case at Lamanai, a small

bat effigy vessel was deposited at the base of a ruined Maya temple prior to construction

of the overlying church platform (Pendergast 1991b: Fig. 16-3b). Besides being an

expression of resistance, it may represent an attempt to “appease(ing) the old gods for the

destruction of their temple” (Pendergast 1991b: 343).

The Lamanai burials themselves attest to the degree to which Maya selectively

adopted features of Christianity. This sample represents the largest skeletal assemblage

from the site, with approximately 179 individuals identified. While sex distribution is

generally equal, there are more Historical period subadults compared to the Postclassic

sample (White et al. 1994).

The first cemetery was located just south of the first church and contained the remains

of more than 25 individuals, who were uniformly adults, suggesting that a separate

children’s cemetery is located elsewhere (Pendergast 1991b).

The second graveyard and church (YDL-85), from which dental remains have been

collected for this analysis, contained individuals of mixed age and sex that are dated to

A.D. 1570-1640. It is believed that both graveyards contain exclusively Maya

individuals (Pendergast 1981, 1986). Owing to their shared circumstances as “reduced”

Maya under Spanish authority, and based on the burial artifacts and bone chemical

evidence (Coyston et al. 1999; White 1986), they are considered similar in

socioeconomic status.

However, for some Maya, this seeming “equality” in death only reflects relative

social circumstances prior to their demise. The fluid nature of population movement and

interactions in the southeastern provinces after Spanish contact suggests that colonial

31

Lamanai was a diverse settlement. Until further analysis is undertaken, the nature of the

archaeological and ethnohistorical records precludes identification of individual Maya in

the colonial cemetery, but it is likely that the Historical assemblage includes: 1)

“commoner” Maya native to Lamanai; 2) members of formerly elite Postclassic

(Lamanai) families; and 3) Maya immigrants from the Yucatan and other adjacent areas,

of varied socioeconomic background. This heterogeneous colonial population likely

experienced dissimilar life experiences prior to arrival at Lamanai, especially childhood

diet patterns and health histories. Such variations may reflect differences in access to

food resources and social relations (power), epidemic disease, famine, re-settlement and

violence associated with the “conquest”.

Despite the Spanish failure to completely stifle Maya beliefs and rituals, there was,

nevertheless, a strict adherence to an entirely Christian mode of burial in the Lamanai

cemeteries at the end of the 16th

century (Graham 1991; Jones et al. 1986; Pendergast

1991b). At Tipu, even after Spanish abandonment of the site (post 1701), the Christian

interment pattern of supine positioning, with the head to the west facing east and with the

hands drawn over the stomach or chest, continued to be practiced in the native Maya

cemetery (Graham 1991; Graham et al. 1989).

To explain this acceptance of Christianity, traditional interpretations, including those

of priests at the time, usually branded the Maya as opportunistic: people who simply

adopted enough Christianity to deceive their oppressors (out of necessity for survival),

without believing what they were taught (see Jones 1989; Graham 1991). At Lamanai,

this is reflected in several caches of Maya religious figurines, which were deposited into

the church platform structure unbeknownst to Spanish clerics (Pendergast 1991b).

32

However, it has become increasingly apparent that Christianity was not “simply a

veneer on a pre-Columbian base” (Graham 1991: 331). Burial evidence, the extent of

religious syncretism of sacred icons, images and rituals, as well as archaeological

indications of regular church maintenance (at Tipu), suggest that despite the preservation

of fundamental Maya beliefs, many colonial period Maya were not superficial, but

practicing, Christians (Graham 1991). Colonial period Maya may have rejected Spanish

autonomy and imperialism, particularly as it was manifest in the clergy, but it appears

that they were active followers of a religion that shared fundamental precepts such as the

heavens, an underworld, an afterlife and multiple religious figures (“saints”) (Farriss

1984).

In total, the syncretism of Christianity with the polytheistic, animatistic Maya religion

demonstrates great resilience in the face of dominating forces. This adaptive ability can

be attributed to the experience of Maya communities with foreigners throughout their

long history, particularly Mexican traders. Time and time again, Northern Lowland

Maya in particular, including Lamanai, encountered visitors who imparted linguistic,

architectural, material cultural and religious influences. In this way, it was a

Mesoamerican tradition that conquering groups introduced new religious cults that

inevitably coexisted with indigenous beliefs (Farriss 1984, 1993). Unfortunately, the root

of much tension between Spanish and Maya lay in this very fact, which was at odds with

the exclusivity of Christianity, a religion that demanded complete dedication, i.e., the

total abandonment of Maya beliefs and deities (Farriss 1993).

Inevitably, the Maya would prevail at Lamanai. Despite being practitioners of

Christianity, according to visiting Franciscan friars Fuensalida and Orbita, the local

33

community destroyed and burnt the church between 1640 and 1641 (Pendergast 1981;

Jones 1989). This rebellion effectively ended Spanish control of Lamanai, as well as

most of Belize, until 1695 (Jones 1989).

Free from the rule of Spanish officials, however, Lamanai Maya continued to revere

the church as hallowed ground, even erecting a stela and traditional Maya altar in the

entrance and nave areas and maintaining ritual activity (Graham et al. 1989; Pendergast

1991b). As Pendergast (1991b: 352) recognizes, “the events that followed the burning of

the church show that although the Spaniards had clearly failed to Hispanicize the Maya,

they had succeeded, probably more fully than they realized, in Christianizing them”.

Slightly later, and until the end of the 17th

century (around 1675), there was limited

and intermittent settlement by one or more families in the masonry chancel of the second

church (Pendergast 1986), as well as south of the main historical period community

(Graham et al. 1989). Thereafter, the site remained abandoned until British colonists

established a short-lived sugar mill between the 1850’s to the early 1880’s.

2.6 The Biological Consequences of Maya-Spanish Contact at Lamanai

In retrospect, the acceptance of Christianity by indigenous Maya, and their

“conquest” by the Spanish in general, can be tied to the psychological and physiological

climate of the time. Prior to contact, widely known Maya prophecies foretold of

impending foreign invasion and catastrophe (Landa in Tozzer 1941; Roys 1933, 1954).

Upon subjugation by Spanish conquistadors, foreign microbes aided in the eventual

decimation of many indigenous groups, primarily affecting vulnerable young and elderly

individuals.

34

As elsewhere in the New World, Maya populations were substantially diminished

after Spanish contact. Unfortunately, this era was also preceded by a series of natural

disasters in the Yucatan that would weaken indigenous survival thereafter. In this way,

the Maya Katun Prophecies of the Books of Chilam Balam refute the notion of pristine

health among indigenous groups before Spanish contact (see Roys 1933, 1954). In

particular, a series of famines and epidemics, most likely pneumonia, greatly affected

Maya demographics around A.D. 1400 (Landa in Tozzer 1941). These events followed

record droughts and locust swarms that devastated maize crops (Roys 1933, 1954).

Epidemic infectious diseases are thought to have been introduced into the Maya area

in 1517, when Spanish soldiers and their African slaves, both probably stricken with

smallpox, arrived in the Yucatan from Cuba (Clendinnen 1987). Between then and the

founding of Merida in 1542 and Bacalar and Valladolid in 1544 (that is, prior to the

Spanish arrival at Lamanai), the Maya population in the Yucatan declined from a

conservative figure of at least 800,000 to about 250,000 survivors (Clendinnen 1987;

Farriss 1984).

Notable epidemics in the Yucatan occurred in 1566, 1569-1570, 1575-1576, 1609

(typhus), 1648-1650 (yellow fever, smallpox), 1659 (measles, smallpox), 1692 –1693 and

1699 (Farriss 1984: 61). Famines in the same area are documented for 1535-1541, 1564,

1571-1572, 1575-1576, 1604, 1618, 1627-1631, 1650-1653, 1692-1693, and 1700

(Farriss 1984).

Worse yet, in the rest of Central America beyond the Yucatan and Belize, a

population loss of almost 90% has been estimated for the period between 1520 and 1580

(Gerhard 1979; Lovell 1985). In Guatemala, The Annals of the Cakchiquels document

35

three major epidemics that depleted native populations after the ‘Great Revolt’ of 1498.

In 1523, 1559-1562 and 1576, entire towns were wiped out by infectious disease,

documentation of which suggests death by influenza (McBryde 1940), measles or

smallpox (Cook 1998).

All told, Old World epidemics of smallpox, measles, influenza, bubonic and

pneumonic plague, yellow fever, typhus and cholera were primarily responsible for

native deaths by infectious disease in the post-Columbian New World (see Cook 1998;

Dobyns 1983; Denevan 1992; Verano and Ubelaker 1992, among others). Three

introduced parasitic infections that could have been the greatest potential contributors to

debilitating anemia include dysentery (Manter 1967; Schmidt and Roberts 1981), malaria

and hookworm (Bruce-Chwatt 1965; Dunn 1965; Friedlander 1977).

Unlike the intensively colonized Yucatan, however, in the southeastern Maya

frontier, early records indicate that political territories remained viable during early

colonial times despite the economic and demographic collapse (Jones 1989).

Nonetheless, the frontier provinces also suffered from epidemics of smallpox, yellow

fever and malaria (see Cook 1998; Farriss 1984; Gerhard 1979; Jones 1989).

In the case of Lamanai, the site’s location put it on a route of potential rapid

transmission of disease. As a frontier for runaways and an outpost in the visita system, it

was likely the refuge of fleeing Maya infected with disease (Pendergast 1991b). For

instance, at Tipu, during the “great general famine” of 1647 to 1650 in the Yucatan,

which followed one of the worst smallpox epidemics in the peninsula’s history, many

Maya migrated to the site in search of food and shelter (Jones 1989).

36

Hard tissue evidence reflects the deterioration of population health in the early

Historical period. For instance, enamel histology, in the form of defective Wilson bands,

indicates that Lamanai Maya suffered more severe, acute, episodic stresses during

colonial times (Wright 1990). Wilson bands appear as darkened bands of enamel in SEM

sections and represent brief periods of ameloblastic growth disruption (Rose 1977, 1979).

The Lamanai historical sample is distinguished by three times more Wilson bands

than Postclassic teeth (Wright 1990). Overwhelmingly, they occur in Lamanai teeth at

the time of weaning. (Microdefect evidence does not reflect a universal colonial

experience however. Historical Maya at Tipu actually have less Wilson bands on average

than pre-contact Maya [Danforth 1989]. This likely reflects differing socio-political

climates: Tipu was not a “reduced” community like Lamanai and was only marginally

controlled by Spanish authorities [Cohen et al. 1994; Graham et al. 1989].)

The mean number of shallow enamel hypoplasias per Lamanai individual is also

significantly higher in Historical individuals compared to earlier periods, and such dental

defects also peak at the time of infant weaning (Wright 1990). The higher rate of such

shallow defects reflect chronic, low-grade stress, and contrasts White’s (1986) findings

for more severe enamel hypoplasias, which are not significantly different from earlier

periods (nor differentiated by age or sex).

Together, the prevalence of Wilson bands and enamel hypoplasia indicate the co-

existence of different kinds of stress in early childhood: brief episodes of severe stress

within periods of chronic low-level health disturbance (Wright 1990). The nature of

Wilson bands is thought not to reflect the epidemics that were recorded ethnohistorically

elsewhere, but rather, lesser childhood developmental disturbances that were survived.

37

The sources of such short-term, acute, ill health are thought to be malaria and Old World

parasitic infections (Wright 1990).

Skeletal evidence of anemia or infectious disease, in the form of porotic hyperostosis,

also indicates that colonial period Maya of both sexes experienced significantly greater

physiological stress (17.0% of Historical Lamanai Maya adults, compared to 9.0% of

Postclassic adults) (White 1986; White et al. 1994). At Lamanai, anemic conditions,

particularly among women and children, might have arisen from several interrelated

factors, namely helminthic or other parasitic infections, heavy reliance on an iron-poor

maize diet, and excessive fluid loss in a tropical climate (White et al. 1994). (Additional

risk factors for women, such as blood loss from menstruation and increased iron needs

with parturition, were postulated for sex differences in porotic hyperostosis prevalence

among adults, but no distinctions were observed [White 1986].)

European diseases such as dysentery, malaria and hookworm could have been the

major causes of anemia and porotic hyperostosis (White et al. 1994). Such skeletal

evidence supports an epidemiological climate of chronic stress in Historical times. The

chronic nature of porotic hyperostosis indicates that either children were increasingly

subjected to infectious disease or that there was a greater likelihood of survival from

early illness (White et al. 1994). Importantly, White and colleagues (1994) believe that

the combined skeletal and dental data reflect a common weaning age, between two and

six years, and the period of highest risk for infectious and parasitic diseases among

children.

Due to the pathogenic attack, it is likely that Maya at the time of contact were also

victims of psychological trauma (despair, suicide) that further eroded physiological well-

38

being and survival (following Blakey 1994; Locke and Hornig-Rohan 1983; Neel 1977).

One way populations respond to witnessing the mass deaths of young and old include

reduced fecundity (see Stannard 1991). Furthermore, loss of older individuals is

particularly detrimental to cultural continuity, since elders are the primary bearers of oral

tradition, i.e., mythology and religion.

Despite escaping death by infectious disease, some survivors still faced other

invisible adversaries. In particular, Maya women, like others elsewhere, were

incapacitated by sexually transmitted diseases. These infections, in addition to smallpox

and tuberculosis, often result in female infertility among survivors (Stannard 1990, 1991;

among others). As elsewhere in the New World, it was both increased mortality rates and

reduced birth rates that led to substantial declines in indigenous population after Spanish

contact.

Numerous lines of evidence offer insight into the nature of Maya diet at Lamanai

after Spanish contact. In general, reduced communities such as Lamanai, which lack the

stability of large established enduring communities, are vulnerable to inconsistent and

unreliable agricultural production (Graham et al. 1989; Pendergast 1991b). This is due to

the fact that reducciones impose heavy burdens on the subsistence activities of the often-

smaller permanent population (Pendergast 1991b: 345).

As a result of disruptions in subsistence practice, as indicated by faunal and floral

data, it has been thought that diet quality may have declined after Spanish contact

(Pendergast 1991b). In particular, the instability of reduced settlements may have

negatively affected agricultural production and diminished per capita intake of protein

39

(i.e., hunting success) (Pendergast 1991b). Such dietary disruptions might account for

some decline in health during the historical period.

Ethnohistorical records shed light on the diet of Maya from the Cholti-Lacandon area

south of Lamanai (Hellmuth 1977; Thompson 1938) and those from the Yucatan (Landa

1566, in Tozzer 1941; Martinez Hernandez, in Marcus 1982). In addition, the Maya

codices and the sacred Quiche Maya text, the Popul Vuh, are invaluable documents. All

such sources point to the sacred role of maize in human creation and subsistence. As a

staple, its cultivation dictated daily activities and resonated throughout all aspects of

Maya culture.

By the time of Spanish contact, however, it appears that most forms of intensive

maize agriculture, i.e., raised fields, terracing, hydraulic agriculture, drained fields and

other irrigation systems, were abandoned, with only traditional slash and burn (milpa) or

swidden cultivation of mixed crops utilized (Marcus 1982; Tozzer 1941). At the same

time, maize shortages were recorded throughout the Yucatan, as well as regions of the

Lowlands toward the Gulf of Honduras and the Lacandon area of Chiapas, Mexico

(White 1986).

Exacerbating the natural disasters that diminished maize production (drought, locusts,

crop disease), Spanish forces also held campaigns to intentionally destroy fields and

homes (Archivo General de Centro America 1937, in Hellmuth 1977). Once reduced to

Spanish-controlled territory, Maya were forced to increase maize production. In the early

18th

century, such intensified cultivation was necessitated by imposed taxation, export

demands and personal consumption (Hellmuth 1977). As a result of crop failure and

purposeful destruction, sometimes by the Maya themselves, many Maya also relied on

40

root crop (jicama) (Roys 1933) and breadnut (ramon) consumption (Puleston 1982),

which were considered either poisonous or unwholesome by the Spanish (Roys 1933).

Nevertheless, bone chemical evidence suggests that dietary quality did not

significantly change from the Postclassic to Historical period at Lamanai, with continued

high maize dependency and supplementation with land herbivores and aquatic resources

(White 1986; White and Schwarcz 1989). Compared to the Classic period, however,

Postclassic and colonial faunal diversity was reduced. Faunal evidence indicates

continued heavy consumption of large turtles (Dermatemys), fish and birds (turkey,

curassow) for all social strata (Pendergast 1991b: 345), but this is accompanied by a

reduction in large mammal (peccary, deer) exploitation (Emery 1999).

The Lamanai dietary evidence, indicating dietary stability from pre-contact to post-

contact times, suggests that while cultural changes were indisputably significant to Maya

lifeways, it was not sufficient enough to alter dietary and agricultural practices in the

early Historical period (White et al. 1994). [Still, as reflected in enamel Wilson bands,

the arrival of Old World infectious diseases was enough to change epidemiological

conditions among indigenous Maya (White et al. 1994; Wright 1990).]

2.7 Bone Chemical Evidence of Diet at Lamanai

Advantageously, bone chemical analyses by White (1986) provide a hard tissue

comparison for LA-ICP-MS results. Lamanai bone chemistry indicates that from the

Preclassic to Early Classic period, strontium levels were decreasing, suggesting increased

maize intake, which comprised 50% of the total diet. This trend eventually reverses

during the Late to Terminal Classic when strontium levels rise, pointing to increased

41

consumption of other, non-maize, foods as important dietary sources. At this time, maize

consumption declined to 37% of the diet (White 1986: 297).

In the Postclassic, this trend reverses, with bone isotopic signatures indicating that

maize consumption at Lamanai reached its highest level, comprising two-thirds or more

(up to 70%) of the diet (White 1986, 1988; White and Schwarcz 1989). In terms of

elemental composition, fresh maize (and especially alkali-processed maize) is notable for

having very low strontium levels (see Chapter Four). In Mesoamerica, maize was, and

continues to be, widely consumed after alkali processing with calcium hydroxide (lime),

which improves nutritional quality and facilitates absorption (Katz et al. 1974). The

effect of maize consumption on enamel element composition during infancy is discussed

in Chapters Four, Five and Seven.

Postclassic evidence of high maize consumption is accompanied by bone chemical

and faunal evidence that suggest minimal exploitation of available lagoon resources and

reliance on fewer animal species (fish, turkey, curassow) (Emery 1990, 1999).

After Spanish contact, 15

N and 13

C analyses of bone suggest that Maya dietary

habits, and presumably agricultural practices, were minimally affected (White 1986).

Isotopic values of historical period remains suggest that maize consumption continued to

dominate 60-70% of the diet (White 1986), which mirrors ethnographic observations of

contemporary Maya diet (Benedict and Steggerda 1937).

At this time, as previously in the Postclassic, children were consuming the same high

level of maize as adults and were likely surviving on diets marginal for protein and iron

(White 1986; White and Schwarcz 1989). As White (1986) notes, such high intake of

protein-deficient maize would have had significant repercussions for children, whose

42

protein requirements are higher than those of adults. In fact, children cannot consume

enough maize to meet their protein demands without adequate supplementation (Behar

1968). Combined with the fact that children are rarely weaned onto a diet containing

meat, Lamanai children likely suffered from illnesses related to protein calorie

malnutrition and iron deficiency anemia (White 1986, 1988). Indeed, this is supported by

skeletal and dental pathologies such as porotic hyperostosis and enamel Wilson bands.

Overall, Postclassic and Historical samples indicate the same level of heavy maize

reliance, with protein supplementation from deer, peccary, fish, turtle and seasonal

exploitation of freshwater mollusks (Emery 1986, 1999; White and Schwarcz 1989).

Dental evidence, in the form of high caries incidence and substantial calculus deposits,

also support the conclusion of dietary stability (White 1986; White et al. 1994). In

White’s (1986) opinion, such evidence refutes the notion that Spanish demands for

increased labor, including that of women, impacted Maya subsistence activities.

2.8 The Repercussions of Maya-Spanish Contact on Infant Nutrition

The myriad dynamic processes that characterize Maya-Spanish contact, i.e.,

resistance, syncretism and transculturation, ecological, biological and cultural

devastation, undoubtedly had numerous consequences on children’s health. Even though

subsistence strategies at Lamanai were not significantly affected, Spanish demands for

increased labor may have affected maternal care and infant health, and this is an

important subject of inquiry in this study.

In ancient times (e.g., Postclassic), it was likely that Maya mothers breastfed their

infants for periods of up to four years (see Chapter Five). While supplementation with

43

non-breast milk foods likely began after six months of age, due to diminished nutritional

quality of breast milk, prolonged nursing is indicated by ethnohistorical sources (Tozzer

1941).

With Spanish colonization, it is postulated that socio-politico-economic factors

altered infant feeding patterns, with dire consequences for children. Historical

documents reveal that Spanish extortions of tribute from Maya men and women greatly

exceeded the legal limits of the colonial system (Graham et al. 1989: 1255). Besides

textiles, agricultural products were in significant demand (Clendinnen 1982; Graham et

al. 1989; Restall 1995). Spaniards took up residence in Maya towns to oversee

collections, but local Maya officials primarily organized the political, economic and

religious administrations alongside Spanish authorities (Graham et al. 1989; Pendergast

1991b). Lamanai and Tipu Maya themselves participated in the exchange of European

products throughout the Yucatan peninsula, which involved Spanish priests, secular

authorities, Maya merchants and Maya migrating from the Yucatan to the southeastern

frontier (Graham et al. 1989).

In this new, colonial, socio-economic climate, the survival of Lamanai children was

compromised. A significant factor may have been reduced lactation and earlier weaning

age resulting from Spanish demands on female labor for cotton trade goods (see

Clendinnen 1982; Restall 1995; White 1986). Such demands on women’s time and

bodies may have undermined childcare practices and further impacted on the health and

survival of infants who were increasingly stressed in historical times, according to bone

and dental evidence (White et al. 1994; Wright 1990). Changes in weaning behavior can

be recognized in the strontium composition of secondary canine enamel, which reflects

44

relative breast milk intake and food supplementation during infancy and early childhood

(see Chapter Five).

On the other hand, native resistance to colonial conditions may have sustained

traditional childrearing practices. It is possible that Maya women resisted Spanish

demands on their time by maintaining intensive childcare practices such as prolonged

breastfeeding. This continuity would be an extension of the preservation of traditional

Maya subsistence overall, which is indicated by bone chemical evidence (White 1986).

In this case, enamel strontium would continue to indicate a prolonged, gradual, reduction

in breast milk intake accompanied by increasing food supplementation.

As the most vulnerable members of a society, children’s health and nutrition are

impacted by changes in almost every aspect of their social and physical environment. At

Lamanai, the cultural, physical and epidemiological upheaval of Spanish colonization

provides a dynamic backdrop to observe the physiological consequences on indigenous

populations. Importantly, teeth provide reliable hard tissue records of an individual’s diet

and nutrition during childhood and can document invaluable life history during such

turbulent historic times. The applicability of dental tissue analysis to paleonutritional and

archaeological reconstruction is discussed in Chapter Three.

Finally, as will be discussed in Chapter Five, it is clear that the nature of infant food

supplementation, breast milk consumption and weaning has significant ramifications for

adult survival and population health status. The effect of colonization on indigenous

infant feeding is thus a vital question in reconstructions of the Maya past.

45

CHAPTER 3

DENTAL HARD TISSUES

AND THEIR APPLICATION IN PALEONUTRITIONAL RESEARCH

3.1 Dental Anthropology in Archaeological and Paleonutritional Reconstruction

For as long as researchers have analyzed human remains to understand the past, teeth

have proven to be invaluable pieces of evidence. More so than bone, which is prone to

physical and chemical degradation, teeth can provide a wealth of biological information

that far exceeds their relative proportion in the human skeleton. As evidenced in the

literature, dental anthropology maintains a significant role within physical anthropology

and archaeology (e.g., Alt et al. 1998; Brothwell 1963; Cruwys and Foley 1986;

Goodman and Capasso 1992; Hillson 1986, 1996; Kelley and Larsen 1991; Moggi-

Cecchi 1995; Scott and Turner 1997).

Teeth can shed light on three major areas of archaeological inquiry. These research

fields are equally assisted by both the macroscopic nature of teeth, as well as the inherent

chemical composition of dental tissues. The first concerns the strong genetic basis of

dental growth and development, which renders teeth an important marker of genetic

affinity (‘biodistance’) and population dynamics (e.g., Hanihara 1979; Hillson 1996;

Jacobi 2003; Lang 1990; Lukacs 1989; Lukacs and Hemphill 1991, 1993; Turner et al.

1991; Scott and Turner 1997). Studies have examined metric and non-metric dental traits

to reconstruct evolutionary history; the nature of group boundaries and movement of

46

individuals; as well as the role of population structure on ancient health and nutrition (see

Larsen 1997).

Chemically, distinctions in dental isotopic signatures (e.g., strontium and lead) related

to geological environment can also be used to trace population movements and origins

(Budd et al. 1996; Sealy et al. 1995; Grupe 1995; Grupe et al. 1997; Gulson et al. 1997;

Montgomery et al. 1998; Price et al. 1994, 2001; Prohaska et al. 2002; Reid et al. 2001).

This is an area of significant advancement in archaeology, as well as modern biological

and forensic science (e.g., Tremlett 2003).

Teeth also reflect general health status during dental development. Beyond indicating

the age at death, an individual’s health, hygiene and nutritional history can be indicated

by pathological conditions such as enamel hypoplasia, hypocalcification, caries,

periodontitis, abscesses and Wilson bands, in addition to non-pathological calculus

deposits (Cohen and Armelagos 1984; Danforth 1989; Goodman and Capasso 1992;

Goodman and Rose 1990; Lukacs 1992; Marks and Rose 1985; Rose 1977; Wright 1990;

among many others).

Additionally, retardation of growth and development due to environmental pollutant

exposure (e.g., lead) during childhood can be discerned from dental chemistry (Budd et

al. 1996, 1998; Evans et al. 1994; Fergusson and Purchase 1987; Goodman et al. 2003;

Outridge et al. 1995; Sharon 1988; Tunstall and Amarasiriwardena 2002).

The third, and most significant, contribution teeth provide for archaeological

reconstruction is paleodietary inference. As the fundamental mechanism directly

involved with mastication, teeth provide dietary biographies at two levels: macroscopic

evidence associated with food intake and inherent chemical composition. Macroscopic

47

indicators such as caries and calculus give a generalized account of relative carbohydrate

(e.g., maize) consumption. Likewise, dental morphology, attrition and wear patterns

provide general indications of dietary components and food preparation techniques

(Brace 1995; Brace and Mahler 1971; Cohen and Armelagos 1984; Grine and Kay 1988;

Harmon and Rose 1988; Lalueza Fox et al. 1996; Lukacs and Pal 1993; Molnar 1971;

Molnar and Molnar 1990; Powell 1985; Teaford 1991).

In contrast, the chemical composition of teeth provides direct evidence of food intake.

Chemical analyses offer both qualitative and quantitative inferences of paleodiet and

represent an evolution of dental anthropology in paleonutritional research. As mentioned

in Chapter One, the assumption that hard tissue chemistry accurately reflects the

chemical composition of consumed plants and animals is central to its application in

paleodietary research.

The analytical chemistry methods used to evaluate hard tissue chemistry and

paleodiet have traditionally involved bone collagen and bone mineral using mass

spectrometric (atomic absorption spectroscopy [AAS]), X-ray fluorescence (XRF), and

neutron activation techniques (see Curzon and Featherstone 1983; Gilbert and Mielke

1985; Price 1989a; Sandford 1993a). Other methods of hard tissue analysis include

isotope dilution-thermal ionization mass spectrometry (ID-TIMS) and proton induced X-

ray emission (PIXE) (Ahlberg and Akelsson 1976; Chaudhri and Ainsworth 1981;

Johansson et al. 1995; Lane and Peach 1997).

For trace element analysis of hard tissues, X-ray fluorescence and atomic absorption

spectroscopy have been the most widely used, with AA more popular due to its

availability and operation ease. However, AA analysis is hindered by its inability to

48

quantify multiple elements at the same time. As a result, the development of inductively

coupled plasma-atomic emission spectroscopy (ICP-AES) and inductively coupled

plasma-mass spectrometry (ICP-MS), which evolved from ICP-AES, have become

popular analytical methods due to their multielement capabilities, speed, and high

sensitivity.

Unfortunately, the traditional means of sample introduction to AAS, ICP-AES and

ICP-MS entail destruction of important time dependent information, which often involves

crude mechanical sampling and dissolution of bulk dental tissues (see Chapter Six). This

fails to capture the subtle gradations in composition, and thus, dietary intake, that is

inherent in sequentially calcified dental tissues.

Due to the compactness of teeth and the depth of stored biological data, the analysis

of dental tissues ideally requires microsampling techniques. The most suitable methods

currently available include laser sampling coupled with mass spectrographic analyzers

and electron or proton microprobes with X-ray emission detectors (e.g., PIXE) (Outridge

et al. 1995). According to Outridge and colleagues (1995: 164), laser ablation (LA) ICP-

MS may be the “most promising microprobe technique for quantitative elemental

analyses of biological microstructures”. This approach is utilized for this analysis and is

elaborated in Chapter Six (Methodology).

49

3.2 Dental Hard Tissues and Enamel Development

Human dental development is characterized by seven main physiological stages:

1) bud; 2) cap; 3) bell; 4) dentinogenesis; 5) amelogenesis; 6) appositional dentine and

enamel maturation (resorption); and 7) eruption.

The initial “bud” phase of (deciduous) tooth germ development takes place at about

six weeks after fertilization, when mesenchyme cells assume arch-shaped zones along the

developing jaws, while epithelial cells form the ten “swellings” in the jaw that will

become the enamel organs for deciduous teeth (Hillson 1996). Epithelium is the layer of

tissue that lines an embryo’s developing mouth. Underlying this layer are mesenchyme

cells, which will ultimately develop into the connective tissues of the body: bone,

cartilage, muscle, tendons, blood vessels, dentine and cementum.

The cap stage is characterized by the proliferation of dental tissues. At this time,

mesenchyme cells form the dental papilla and dental follicle, which will develop into

odontoblasts (dentine forming cells) and cementoblasts (cementum forming cells),

respectively. Later in this stage, the enamel organ differentiates into the internal enamel

epithelium, which will eventually differentiate into ameloblasts and form enamel matrix .

During the bell stage, dental cells differentiate further. Now, odontoblasts develop,

which secrete predentine matrix, and inner enamel epithelium cells differentiate into

ameloblasts, which secrete enamel matrix on top of the predentine. The enamel organs

are fully differentiated by the fourth month in utero, with dentinogenesis and

amelogenesis taking place soon afterwards (see below).

Human teeth are composed of three different hard tissues, namely cementum, dentine

and enamel (see Figure 3.1). Cementum is the thin calcified layer that covers tooth roots,

50

while dentine makes up the interior of tooth crowns and roots, and enamel forms the

crown exterior. Comparatively, mature enamel is the most inorganic: 97-98%

hydroxyapatite, with no organic collagen component. Dentine and cementum have a

lower inorganic component: 75% and 65%, respectively, which resembles bone (65%).

Rose et al. 1985

Figure 3.1 Cross-section of human tooth, with major anatomical features indicated

Cementum is the thin layer of bone-like connective tissue that surrounds the dentine

of tooth roots and forms the connecting tooth plates of dentine and enamel.

Ultrastructurally and biomechanically, it resembles bone, which is why it is often called a

bone of attachment (Scott and Symons 1974). Owing to their shared mesenchymal

origin, the apatite crystals of cementum are similar in size and composition to those of

bone and dentine. Likewise, cementum is mesodermal (mesenchymal) in origin, with a

collagenous organic matrix. Inorganic apatite comprises approximately 70% by weight

of cementum, with 24-26 wt % being organic content, and water amounting to 4-6 wt %

(Carlson 1990: 534).

51

Dentine is formed by odontoblast cells and makes up the interior of tooth crowns and

roots. It is the first dental tissue to mineralize, followed by enamel and cementum. Like

bone and cementum, dentine is a mesodermal, mineralized, connective tissue. Compared

to enamel, it is less inorganic (70-75 wt %), with an 18-21% organic component made up

of collagenous proteins, and the remaining 4-12 wt % composed of water (Carlson 1990:

533). Moreover, dentine in contact with the pulp cavity, or secondary (circumpulpal)

dentine has an even higher organic content. Unlike enamel, but comparable to secondary

cementum, secondary dentine continues to develop during the lifetime of a tooth.

Overall, dentine is less dense and more permeable than enamel.

The inorganic component of bone, cementum, dentine and enamel consists of calcium

phosphate crystallites, which mineralize after organic matrix secretion. Human hard

tissue crystallites are a carbonate hydroxyapatite, which are apatite minerals. Apatite

refers to a diverse group of phosphate minerals sharing the same basic structural type:

A4B6(MO4)6X2. Typical biological apatite contains calcium ions in both the A and B sites

of the lattice; a phosphate group such as PO4 in the MO4 position, and hydroxyl (OH) or

other ions in the X position (Carlson 1990: 531). The resulting chemical formula for the

inorganic crystal lattice of human bone and dental tissues is Ca10(PO4)6(OH)2 (see Figure

3.2).

Figure 3.2 Three-Dimensional

Chemical Configuration

of Hydroxyapatite

[Ca10(PO4)6OH2]

52

Apatite crystallites in dentine resemble those of bone in size and dimension,

averaging 2-4 m in length, and 0.3 m in width (Carlson 1990). This is noticeably

smaller than enamel crystallites, which range from 16-100 m in length, and 4 m in

width (Carlson 1990).

Finally, enamel is the hardest human tissue and it differs fundamentally from both

dentine and cementum. Notably, enamel derives from ectodermal (epithelial) fetal

tissues and has a non-collagenous organic matrix. It is formed by protein-secreting

ameloblasts from the inner enamel epithelium. Ninety per cent of the organic component

is amelogenin, which are proteins unique to enamel matrix.

While highly inorganic and hard when mature, enamel starts off as a porous

crystalline matrix filled with water and organic material inhabiting intercrystalline

spaces. Water, proteins and lipids form the aqueous matrix that surrounds enamel

crystals, which totals approximately 3-4% of mature enamel by weight (almost 15% by

volume) (Curzon and Featherstone 1983). Specifically, water amounts to approximately

2% of enamel by weight (12% by volume) (Carlson 1990), while organic material makes

up the remaining 1% by weight (2% by volume) (Jenkins 1978).

Enamel growth corresponds with dentine, which develops from adjacent odontoblast

cells. In general, the rate of enamel deposition is stable unless physiological disruptions

affect ameloblast secretion. In humans, the rate of enamel matrix secretion is estimated

at 4-4.5 m per day (Schour and Hoffman 1939; Massler and Schour 1946).

Amelogenesis is characterized by an initial secretion of enamel matrix accompanied

by some (primary) mineralization. Deciduous enamel formation begins at around four

months in utero, with the first tooth eruptions at about six months after birth, and all

53

deciduous teeth fully erupted by about two and a half years. Among permanent teeth,

central incisors, first molars and upper canines commence enamel formation earliest, at

around the time of birth (ending 4.5, 3.5 and 5 years later, respectively), while third

molars are the last developing teeth (generally between 9 and 13 years of age [Anderson

et al. 1976; Moorrees et al. 1963]).

In this study, permanent canine crowns are considered to begin enamel development

at between birth and six postnatal months and be complete by 5-5.5 years of age (see

Appendix A). Some variations in the rate of dental development exist between

populations, as well as between males and females (who are slightly advanced), but the

disparities are minimal, e.g., 2-3%, and are not considered significant (see Appendix A).

During the initial migration of ameloblasts from the dentine substrate, cone-shaped

Tomes’ processes develop at the end of each cell. With the completion of amelogenesis,

these processes eventually become reduced and disappear, resulting in a thin layer of

non-prismatic enamel at the enamel-dentine junction of the enamel surface (Scott and

Symons 1974).

Upon reaching full enamel thickness, ameloblasts switch from enamel matrix

secretion to absorption of protein and water. This subsequent phase of enamel

maturation, or secondary mineralization, results in chemical and structural changes to

enamel. It is a protracted and complex process that is thought to involve three phases of

calcification, starting from the surface to the dentinoenamel junction and then back

toward the surface, finalized by tertiary mineralization of the narrow subsurface layer,

which is the most mineralized of all enamel layers (Suga 1982).

54

Mineralization begins in the earliest secreted enamel at the dentine junction and then

extends outward as newly formed (immature) enamel develop. These “gradients of

mineralization” extend over many weeks in any one part of the developing crown

(Beynon et al. 1998: 353). It progress in an occluso-cervical direction and can vary in

timing depending on location, e.g., lateral tooth surfaces (buccal cervix) take longer to

mineralize than inner approximal enamel (Beynon et al. 1998; Liversidge 1995).

Unfortunately, enamel mineralization research currently cannot attribute a precise

time period for the complex process in permanent teeth (L. Humphrey, personal

communication, 2004), especially considering the extent of intratooth variation. The

main challenge has been the inability of radiographic techniques to identify the earliest

stage of enamel calcification, which is overestimated by X-rays (Hess et al. 1932;

Winkler 1995), while it underestimates the age of crown completion (see Beynon et al.

1998; Liversidge 1995).

Importantly, in this study, it must be remembered that relative age of individuals is

based on incremental enamel structures, which are the result of the first, mostly organic,

stage of enamel formation. The maturation phase witnesses the bulk of enamel

mineralization and it is the main period measured when elements such as strontium and

calcium are quantified by LA-ICP-MS. Since mineralization occurs over several weeks

after enamel deposition, this time delay is a source of error that must be recognized in

this investigation. However, until further research elucidates the timing of the maturation

process, the significance of this factor is uncertain.

During mineralization, the majority of crystal growth of the already initiated enamel

crystallites occurs (growing to 5-10 m in diameter), and the amino acid composition of

55

enamel protein changes (Carlson 1990; Hillson 1996). With a considerable decrease in

the volume of organic material and water, enamel matures into a harder and denser

calcified tissue that is almost 97 % inorganic by weight (86% by volume) (Curzon and

Featherstone 1983). Strontium is one element that is primarily incorporated in enamel

during the maturation phase.

For the purposes of this study, it is the inorganic composition of dental enamel that is

most relevant for elaboration. The inorganic component of human enamel is organized at

three structural levels: 1) the individual apatite crystal, 2) bundles of crystallites, or

enamel “prisms”, and 3) Hunter-Schreger bands, or prism layers.

Enamel apatite crystals are approximately 3-4 m in diameter and 10 m or more in

length (Orams et al. 1976). Similarly oriented apatite crystals occur in long clusters of

tightly packed hexagonal prisms or “rods”, which are roughly perpendicular to the tooth’s

surface. They arise from the dentinoenamel junction and extend to just below the surface

of the tooth. Enamel prisms are the morphologic unit of enamel and they can differ in

size, shape, orientation and relative density. Importantly, enamel apatite crystals are

imperfect structures and contain calcium deficient areas (Featherstone et al. 1981b).

Metal ions (e.g., strontium) or metal-fluoride complexes can incorporate in these

deficient areas and are an important component of enamel (see below).

Hunter-Schreger bands are layers of similarly oriented enamel prisms that are parallel

to one another but angled differently from prisms in adjacent bands. Such bands are also

differentiated by prism shape (Carlson 1990).

Morphologically, tooth crowns develop as fronts of corresponding enamel and

dentine bands (see Figure 3.1). Enamel growth bands appear histologically as successive

56

Striae of Retzius, which are regularly spaced, at 30-40m apart in the occlusal half of the

crown, and 15-20m apart in the cervical half (Hillson 1996). These striae record the

variable activity of ameloblasts during amelogenesis.

Physiological stressors during enamel development can result in pronounced,

darkened, striations. The neonatal line is a pronounced stria of Retzius that records the

time of birth in deciduous teeth and permanent first molars (Schour 1936) and can offer

insight into the relative timing and rate of dentine and enamel development before and

after this event.

Between adjacent striae of Retzius, there are approximately 7 to 8 cross-striations

(Newman and Poole 1974), or “pinch and swell” structures, spaced at regular intervals

about 4 to 8 microns apart along the length of enamel prisms (Boyde 1976). Current

research indicates a range of 6 to 12 cross-striations between brown striae of Retzius

(Beynon 1992; Bromage and Dean 1985; Bullion 1987; FitzGerald et al. 1996). Cross-

striations are caused by cyclical variation in the rate of enamel matrix secretion, with

swellings representing faster secretion, and constrictions, reduced secretion (Boyde 1976,

1989). The spacing of cross-striations in human teeth correspond well with the estimated

enamel matrix secretion rate of 4-4.5 m per day (Schour and Hoffman 1939; Massler

and Schour 1946), as well as with independent estimates for crown formation time (see

Hillson 1996). As a result, enamel cross-striations are thought to represent a 24 hourly,

or circadian, rhythm (Boyde 1976; Dean 1987; FitzGerald 1995, 1998), while striae of

Retzius represent weekly developmental features (Newman and Poole 1974).

57

3.3 Dental Enamel Composition

Since dental enamel is primarily inorganic, the analysis of enamel composition is

primarily concerned with elemental concentration. Elements fall under two main

categories: bulk elements (or macrominerals) and trace elements. They can be

cumulative in human hard tissues, e.g. lead, or they can fix in tissues up to a threshold

level, at which point the majority of the intake (or surplus beyond the needs of the

organism) is excreted in hair, urine, perspiration and/or feces. In this case, the element

maintains a relatively constant level within species.

In the human body, more than 99% by weight is composed of carbon (C), hydrogen

(H), oxygen (O), nitrogen (N), sulphur (S), phosphorus (P), calcium (Ca), magnesium

(Mg), sodium (Na), potassium (K) and chlorine (Cl), which are bulk or macro elements.

The first six bulk elements (C, H, O, N, S, P) form the major nutrients, namely proteins,

lipids, carbohydrates and nucleic acids. All bulk elements are essential for life.

Trace elements are minerals that occur in amounts of less than 0.01% of the body

mass. They can be separated into three categories: essential trace elements, metabolic

trace elements, and non-essential trace elements. In humans, fifteen elements are

considered “essential” trace elements, which are required for proper nutrition and

development of an individual. They are particularly vital for all biochemical processes

since they are part of important enzymes. All trace elements can be toxic in excessive

amounts, although some are noteworthy for physiological impairment even at low levels,

e.g., cadmium, mercury and lead (Larsen 1997).

Essential trace elements are those that are: 1) present in all healthy tissues of living

organisms; 2) occur in concentrations that are relatively constant between animals of the

58

same species; 3) can induce the same structural and physiological abnormalities and

dysfunctions (specific biochemical changes) in all species if removed from the body; 4)

can prevent or reverse such abnormalities if restored to the body; and 5) can prevent or

reverse such biochemical changes if the element is maintained (its deficiency or excess is

prevented or reversed) (Cotzias 1967). Indeed, both a deficiency and toxicity of essential

trace elements can disrupt body homeostasis and impart adverse physiological effects.

Essential trace elements in humans include iron (Fe), zinc (Zn), copper (Cu),

manganese (Mn), nickel (Ni), cobalt (Co), molybdenum (Mo), selenium (Se), chromium

(Cr), iodine (I), fluorine (Fl), tin (Ti), silicon (Si), vanadium (V), and arsenic (As)

(Underwood 1977). In life, these elements are provided by food and water, but ionic

exchange in the burial environment can also enrich or deplete these elements in fossilized

tissues. Other elements not considered “essential”, but which also play important roles in

human nutrition, include boron (B), barium (Ba), bromine (Br) and strontium (Sr) (see

below).

With fossilized hard tissues, trace elements are studied within the context of the

inorganic portion of bones and teeth, despite their presence in (significantly less) organic

portions. Excluding water and some organic material, the major components of human

dental enamel include Ca, P, CO3 (carbonate), Na, Mg, Cl and K. Enamel is

approximately 36% calcium in content (by weight), while phosphorus, which is present

almost entirely as phosphate, is between 16 and 18% (Curzon and Featherstone 1983).

The following tables outline the concentrations of bulk and trace elements in human

enamel (from Curzon and Featherstone 1983):

59

Table 3.1 Concentrations of major components of human dental enamel

excluding water and organic material

(Curzon and Featherstone 1983: Table 1)

Component Concentration range in percentage

(dry weight)

Ca 33.6-39.4

P 16.1-18.0

CO3 2.7-5.0

Na 0.25-0.90

Mg 0.25-0.90

Cl 0.19-0.30

K 0.05-0.30

Table 3.2 Range of element concentrations in human dental enamel

(adapted from Curzon and Featherstone 1983: Table 2)

Concentration

in ppm Elements

> 1000 Cl, Mg, Na

100-1000 K, S, Si, Sr, Zn

10-100 Al, B, Ba, Fe, Pb

1-10 Br, Cd, Cr, Cu, I, Mn, Mo, Rb, Sn, Ti

0.1-0.9 Ag, Be, Co, Hg, Li, Nb, Ni, Sb, Se, W, Zr

<0.1 As, Au, Bi, Ce, Cs, Dy, Er, Eu, Ga, Gd, Ge, Hf,

Ho, In, Ir, La, Lu, Nd, Os, Pb, Pr, Pt, Re, Rh, Ru,

Sc, Sm, Ta, Tb, Te, Tl, Tm, V, Y

(Together with calcium (Ca), highlighted elements are those quantified by

LA-ICP-MS in this study.)

60

Common trace elements in biological apatite include Al, Ba, Br, Fe, Pb, Sr and Zn.

Elements that exhibit wide variations in enamel include Pb, Mn, Se, Sr and Zn (see

Curzon and Featherstone 1983). The principal source of variation for many elements,

including strontium, in foodstuffs and eventually, hard tissues, is the underlying geology

(see below).

In teeth, there is general compositional homogeneity within enamel growth bands,

with variation more typical of intra-band differences, i.e., between enamel of different

developmental ages (Dolphin et al., in press; Goodman et al. 2003; Kang et al. 2004).

Any enamel chemical heterogeneity that occurs within bands is the result of individual

variation in mineralization during dental development or post-mortem external

contamination.

According to Curzon and Featherstone (1983), trace element composition in enamel

generally does not change during the course of enamel development, although certain

elements merit attention. Of twenty-four trace elements that have been studied for age

changes, fifteen have been observed to remain stable, five generally decrease (Cu, Fl,

Mn, Sr and Zn) and five can increase (Co, Pb, K, Na and Se) (see Curzon and

Featherstone 1983: Table 4). Age-related variations in element abundance can be

attributed to dietary changes (e.g., infant to adult foods), physiological changes (e.g.,

discrimination capacity, pregnancy, lactation), and accumulated pollution exposure.

However, extensive current research suggests that trace element behavior is probably

more complex and variable in humans. For example, strontium levels can increase and

decrease at different ages in the life of an individual depending on nutrition and digestive

system discrimination (see Chapter Four). Infants undergoing the transition from

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exclusive breastfeeding to solid food reliance reflect differences in dietary (and thus hard

tissue) Sr/Ca that is due to the clear distinction between breast milk and solid food

strontium abundance. Breast milk has an extremely low Sr/Ca composition, while solid

foods and water have significantly higher concentrations. This fact forms the basis of

this investigation on ancient weaning. At the same time, hard tissue Sr/Ca is recognized

to be age-dependent on gastrointestinal maturation and strontium discrimination, which

develop during early childhood (see Chapter Four).

In light of the multielement analytical capabilities of ICP-MS, Se, Cu, Mn, Ba, Fe, Pb,

Sr, Zn and Mg were quantified from permanent canine enamel (see Table 3.2). Such

elements were chosen for their nutritional implications and potential for future research,

but for this investigation, the primary focus is strontium (Sr) (see Chapter Four).

3.4 Diagenesis and Hard Tissue Preservation

Concomitant with the extensive application of hard tissue chemistry to paleonutrition,

considerable research into the taphonomic processes that govern hard tissue preservation

was undertaken (DeNiro 1985; Ezzo 1994; Grupe and Herrmann 1988; Kohn et al. 1999;

Kyle 1986; Lambert et al. 1984, 1990; Pate and Brown 1985; Pate and Hutton 1988;

Price 1989; Price et al. 1992; Radosevich 1993; Sandford 1993; Sillen 1981, 1986; Sillen

and Sealy 1995; Sillen et al. 1989). Most researchers today recognize that prior to any

hard tissue chemical analysis, some assessment of postdepositional environment and

diagenesis must be determined to control for contaminated remains. Diagenesis is the

sum of all physical, chemical, and biological processes which occur in the post-mortem

62

depositional environment (Price 1989; Radosevich 1993; Sandford 1993; Sillen et al.

1989). All fossilized hard tissues undergo some degree of diagenetic alteration.

In short, the degree to which diagenesis can affect hard tissues is determined

generally by several factors: 1) time; 2) nature of the surrounding geological environment

(groundwater, soil pH, available elements); 3) age of individual at death (subadult bones

are less mineralized/more porous); and 4) type of hard tissue (compact cortical bone vs.

porous cancellous bone; bone vs. teeth) (Parker and Toots 1970, 1980).

Numerous diagenetic mechanisms can degrade the chemical integrity of human hard

tissues, most notably bone. Post-mortem factors include soil pH, organic matter content

(including bacteria, algae and fungi), mineralogy and texture, temperature, soil enzymes,

abundance and distribution of rainfall, and groundwater movement (Pate and Hutton

1988; Piepenbrink 1986; Hanson & Buikstra 1987). Such factors can enrich, deplete or

substitute original biogenic elements in hydroxyapatite by promoting soil element

precipitation and ionic exchange (Kyle 1986; Parker and Toots 1980; Pate and Hutton

1988; Schoeninger 1982).

The availability of insoluble or soluble and exchangeable ions in the soil solution of a

burial environment is the major factor determining whether elements will be chemically

mobile and available for contamination (Radosevich 1993). Ion availability is affected

by factors such as “weatherability” and solubility of a specific mineral, soil porosity, pH,

temperature and precipitation (Mitchell 1957).

The rate and intensity of soil weathering is highly dependent on water and

temperature. For example, exchangeable ions will make a greater contribution to soil

solution, and thus, hard tissue permeation, in more humid (hot and wet) climates, or in

63

areas where irrigation is practiced (Pate and Hutton 1988). In these environments, there

will be rapid weathering and downward soil leaching, compared to arid regions, where

there is slow weathering of bedrock and soils and upward evaporation of groundwater

(e.g., precipitation of calcite).

Soil pH plays a dominant role in determining the availability of various elements to

the soil solution. Bone hydroxyapatite is relatively insoluble at high pH levels (alkaline

conditions), but its solubility increases as pH decreases to 6.5 or 6, and increases rapidly

below a pH of 6.0 (Lindsay 1979; Pate and Brown 1985). Acidity in soil and/or

groundwater can result in the leaching of elements such as Zn, Cu, and Mn from organic

material (Gilbert 1985). Additionally, Mg, Sr and Zn can replace Ca heteroionically

(exchange with natural tissue constituents) at the surface of bone in acidic conditions

(Lambert et al. 1985b).

Lipids, humic acid (decayed plant matter), fulvic acid, and carbonates can also alter

hard tissue collagen isotopic values (Ambrose 1986, 1990, 1991, 1993; Chisholm 1989;

DeNiro 1985; DeNiro and Hastorf 1985; Heaton et al. 1986; Sealy et al. 1987; van der

Merwe 1989). Bone is susceptible to such alteration but tooth enamel is not significantly

affected and can preserve its dietary isotopic signature for up to several million years

(Ambrose 1993: 62).

Overall, the results of many studies indicate that barium, calcium, copper, manganese,

iron, aluminum, phosphorus, potassium, silicon and vanadium are elements that often

exhibit post-mortem alteration (enrichment or depletion) in human bones (Hancock et al.

1987; Keeley et al. 1977; Kyle 1986; Lambert et al. 1979, 1982, 1984, 1985; Parker &

Toots 1970, 1974, 1980; Pate and Brown 1985; Price & Kavanagh 1982; Sillen 1981b).

64

Elements that generally resist significant diagenetic change include magnesium,

strontium and zinc (Ezzo 1994; Kyle 1986; Lambert et al. 1979, 1982, 1984, 1990;

Sandford 1993; among others).

Of the hard tissues, dental remains maintain their chemical integrity most effectively

and are the best-preserved human tissues. Among dental tissues, enamel, particularly

core enamel, is the most resistant to chemical alteration in both the living mouth

environment and the post-mortem diagenetic environment, while dentine is the most

exposed and least resistant to alteration.

Unlike bone and dentine, enamel resists significant diagenetic alteration due to its

highly inorganic, acellular, nature, larger apatite crystal size, greater crystallinity,

hardness, and impermeability (Lee-Thorp 1989; Parker and Toots 1980). These

characteristics render enamel the hardest tissue in the human body, yet at the same time,

it is more brittle and has lower compressive strength than dentine.

The advantage of enamel’s low organic composition is also underscored by the highly

resistant nature of the organic material itself. In this case, the proteins and peptides of

mature enamel are tightly bound into the mineral structure and have been known to

survive in fossil enamel even millions of years old (Hillson 1996: 228).

Fully mature enamel is essentially fixed and removed from contact with cellular

elements, but it is not entirely inert, as ion exchange can take place between saliva and

the surface layer of enamel. Despite the fact that apatite crystals are generally

impermeable and more resistant to diagenetic alteration than bone, enamel prisms can

adsorb ions onto its surface that may eventually become incorporated into the surface

enamel. Major structural elements such as Ca and P, and to a lesser extent, Mg, Na and

65

chloride, remain relatively consistent, but there are substantial differences in carbonate

and trace element abundance (Carlson 1990; Puech et al. 1986).

In the living mouth, the outer few micrometers of enamel are regularly attacked by

acid from plaque bacterial metabolism, resulting in some enamel demineralization. The

partial demineralization that occurs is followed by remineralization as the partially

dissolved crystals “regrow with preferential exclusion of some ions and inclusion of

others” (Curzon and Featherstone 1983: 132). For instance, as a natural protective

mechanism against caries, fluoride, strontium and zinc can be incorporated during

remineralization or maturation of surface enamel (Curzon and Featherstone 1983) (see

Section 4.3 for in vivo incorporation of strontium). Such in vivo incorporation of

elements can be significant, with Reitznerová and colleagues (2000) identifying saliva

de- and re-mineralization of enamel as far as 150 μm from the enamel surface.

After death, enamel elemental composition can also be altered by diagenetic factors.

In particular, ions of barium (Ba), lead (Pb), magnesium (Mg), potassium (K), sodium

(Na) and strontium (Sr) from surrounding groundwater can replace calcium in enamel

crystal structures. Strontium can readily substitute for calcium in hydroxyapatite crystals

because of similar chemical and physical properties (see Section 4.3).

Other notable mineral exchanges in fossilized dental tissues include phosphate

substitution by carbonate ions, substitution of hydroxyl ions by fluorine and chlorine

(Carlson 1990); and enrichment of Fe, Mn, Si, Al, Ba and possibly Cu due to

contamination of enamel and dentine apatite with secondary minerals (Kohn et al. 1999).

Besides enamel chemistry, the post-mortem preservation of enamel can also be

affected on a gross level by the burial matrix. Despite its highly inorganic composition,

66

enamel is susceptible to adverse environmental conditions such as very acid soils.

Enamel can dissolve in such contexts and appear pitted and eroded but, interestingly,

some organic remnants of dentine can withstand the acidity (Stead et al. 1986).

Finally, outside of natural processes of diagenesis, cultural treatment of human

remains is an equally important factor in hard tissue preservation. In cremation, the

enamel of erupted teeth can flake away from dentine, but unerupted teeth are somewhat

protected by their bony crypts, and can retain their enamel (McKinley 1994). The

heating of bone affects its structural composition and isotopic signatures (DeNiro 1985),

but in teeth, limited findings indicate that there are only changes in tooth appearance and

microstructure (Shipman et al. 1984). Reflecting their hard, inorganic nature, enamel

prism structure is still visible even after temperatures of 8000C or more (Shipman et al.

1984).

In light of the evidence, enamel is the ideal hard tissue for chemical and sequential

analysis, and for the present paleodietary study, in particular, because of three main

qualities: 1) it is the best preserved and least diagenetically-affected human hard tissue;

2) unlike dentine and bone, which reflect an elemental signature accumulated just prior to

tooth loss or death, enamel preserves a faithful and indelible record of childhood dietary

(elemental) intake during the period of crown development, which is well understood;

and 3) non-developmental incorporation of elements in enamel can be recognized and

eliminated through several acid washing methods (see Chapter Six), and can be avoided

by sampling inner enamel.

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3.5 The Nature of Hard Tissue Preservation at Lamanai

In light of the various factors potentially disguising the “true” chemical nature of hard

tissues, most notably bone, a sample-specific assessment of diagenesis is required for

archaeological remains. Fortunately, for Lamanai, White (1986) has accounted for

numerous controls (see Beck 1985; Gilbert 1977) to exclude all possibilities of

diagenesis. The skeletal remains of Lamanai individuals from all cultural periods at the

site are notably well preserved for sub-tropical conditions and relatively free of

significant diagenetic alteration (White 1986).

A major precondition for utilizing fossilized hard tissue samples in chemical analyses

is stability of the post-mortem environment. Generally, one can state that hard tissues

will be well preserved in soils of neutral or slightly alkaline pH, while acid soils inhibit

good preservation (Keeley et al. 1977). Low soil acidity (pH>6.5) will indicate low ionic

exchange and fewer available elements for contamination. Reduced exposure to

groundwater will also minimize the availability of exchangeable mineral ions. At

Lamanai, all human remains were buried in matrix above the water table and soil pH was

an acceptable mean of 6.8 (Lambert and Arnason 1984).

Comparison of elemental values between hard tissues and surrounding matrix will

give an indication of chemical stability, particularly trace elements that are known to be

diagenetically altered after deposition (see Keeley et al. 1977; Kyle 1986; Lambert et al.

1979, 1984; Nelson & Sauer 1984; Pate and Hutton 1988; Waldron 1981, 1983). For

instance, significant levels of iron, manganese and lead in fossilized tissues are reliable

indicators of diagenesis (Buikstra et al. 1989; Francalacci and Tarli 1988; Lambert et al.

1990; Runia 1987b; Waldron 1981, 1983). Rubidium and yttrium, which are common in

68

surrounding (calcareous) soil matrix, but normally absent in bone, can also be examined.

In the Lamanai remains, White (1986: 160) found no correspondence between soil and

bone values over time for elements relevant to paleonutritional analysis. Significantly,

for this investigation, Lamanai soil samples exhibit substantially lower Sr levels than

human bone remains (White and Schwarcz 1989: Table 2).

Due to the calcareous geology of the Maya Lowlands, precipitation of calcium into

hard tissues is a major concern (see Pate and Brown 1985). This limestone environment

is rich in calcium carbonate/calcite (CaCO3) and gypsum (CaSO4.2H2O), which are

common pore-filling minerals (White 1986).

Weathered hydroxyapatite in poorly preserved bone will have reduced Ca content,

which can be replaced by Ca ions from surrounding soil, and can actually result in Ca

enrichment (White and Hannus 1983). A high Ca/P ratio can identify calcium carbonate

addition because it results in the dilution of phosphorus (the theoretical ratio of Ca:P for

hydroxyapatite is 2.16) (Sillen 1989; White 1986: 121). Analyses of Ca/P ratios in

Lamanai bone suggest that there is no significant Ca enrichment over time, reflecting

good skeletal preservation.1 Thus, using Ca as an internal control is valid (White 1986).

Simple detection of diagenesis can also be accomplished by comparing different

fossil animal bones of known stratigraphic context at the site. The elemental and isotopic

integrity of hard tissues of animals with well-documented opposing diets can be

compared to test the post-mortem environment (e.g., Nelson et al. 1983; Pate and Brown

1 White (1986) notes, however, that a high mean ash content of 94.4% in Lamanai bones suggests diagenetic loss of organic

material. Leaching of calcium may have occurred, but it is not considered problematic because there is no significant difference in the

Ca/P ratio of Lamanai bones over time (i.e., Ca leaching was constant over time) (White 1986: 159). White (1986) also observed that

absolute and ratioed values of Mg and Sr with Ca were in accordance. While the Lamanai bones may exhibit some Ca leaching, dental enamel is more highly inorganic and resistant to such taphonomic processes and is probably minimally affected in this analysis.

69

1985, Price and Kavanagh 1982; Sillen 1981a, b, 1986, 1992; Wessen et al. 1978; White

1986, among others).

The range of animal species and plant resources available to the population at the

time should obviously be known, and in the case of Lamanai, faunal, paleobotanical,

ethnohistorical and archaeological evidence provide numerous sources of insight. Other

than variations due to semi-domestication (animal maize consumption), differences in

trophic position due to diet (herbivory vs. omnivory vs. carnivory) were clearly

discernible in Sr/Ca values of diverse Lamanai fauna, indicating good post-mortem

preservation (White 1986). Ancient Lamanai fauna also do not exhibit evidence of

significant post-mortem elemental deposition or leaching, and like the human remains,

faunal Ca/P ratios indicate chemical stability over time (White 1986).

In total, soil analysis, faunal controls and comparisons with human bone chemistry

indicate that Lamanai hard tissues are wholly suitable for chemical analysis and are

accurate indicators of in vivo dietary incorporation. Utilization of dental enamel, which

is more completely mineralized and impermeable to diagenesis than bone, means that

external and post-mortem effects on paleodietary research are especially limited. This

fact, combined with the timing of enamel development during a critical stage in life

history, highlights the uniqueness and applicability of dental tissues to health and

nutritional research.

70

CHAPTER 4

THE ROLE OF STRONTIUM ANALYSIS IN PALEONUTRITION

4.1 Strontium Distribution in the Food Web

Strontium (Sr) is a soft, silvery yellow, alkaline earth metal (atomic number 38) that

has a cubic face-centered crystal structure. It was first identified in Scotland in 1790 by

Adair Crawford and William Cruikshank as a component of the mineral strontianite. It

naturally occurs in the lithosphere as four stable isotopes (in order of % abundance): 88

Sr

(82.56%), 86

Sr (9.86%), 87

Sr (7.02%) and 85

Sr (0.56%), with an average atomic weight of

87.63. Fourteen radioactive isotopes of strontium also exist (e.g., 89

Sr and 90

Sr), which

have made strontium the focus of extensive research on nuclear fallout since the 1950’s.

Like other trace elements, its relative abundance in organisms is determined by species-

specific absorption ability and environmental availability, which have important

implications for paleonutritional reconstruction.

Importantly, the consideration of strontium (and other alkaline elements) in living

organisms and their fossilized hard tissues must be viewed as a ratio relative to the total

amount of available calcium (Sr/Ca). Strontium and calcium share a very close, direct,

relationship in living organisms, including shared metabolism and distribution (see

below). (In contrast, Sr has an inverse relationship with Mg, so that the two relationships

[Sr/Ca, Sr/Mg] should be reflected in correspondingly distinct ratios). Significantly, the

amount of Sr absorbed by organisms is wholly dependent on relative dietary calcium

abundance, with high Ca associated with reduced Sr absorption, and vice versa.

71

Consequently, for human dietary research, including understanding trophic level

fractionation, it is the Sr/Ca ratio that is relevant.

Following Beck’s (1985) and Lambert and coworkers’ (1982) suggestion to use

absolute Sr values instead of Sr/Ca ratios, White (1986) has examined both kinds of data

but found that Sr/Ca ratios closely mirrored patterns of absolute Sr values (reflecting

good Ca preservation). This is also the case for strontium data in this investigation.

It is, therefore, important to recognize the Ca abundance of consumed foods, in

addition to the Sr content and Sr/Ca ratio. As outlined by Sillen and Kavanagh (1982:

70), the efficacy of hard tissue Sr/Ca ratios for paleodietary research is determined by

“a) the Sr/Ca ratios entering food chains via water and plant foods, and b) the degree and

number of discrimination steps to which alkaline earths are subjected before reaching

human skeletons”.

In the natural environment, strontium is introduced at the plant level, through soil and

water, and is successively discriminated against as one moves up the food chain.

Specifically, Sr is found in the minerals celestite and strontianite. Variables in the

underlying geological substrate of the local environment will determine the amount of

strontium available to plants and animals (Toots and Voorhies 1965). Such factors,

which ultimately affect the Sr/Ca ratio of groundwater, include: 1) concentration of trace

elements in the parent rock; 2) rate and extent of weathering; 3) drainage of soils; and 4)

soil pH (Mitchell 1955, 1957).

Rocks such as shale and granite have the highest Sr/Ca ratios, while limestone

(calcium carbonate), despite having a high absolute concentration of Sr, has a low Sr/Ca

ratio due to a much higher abundance of Ca (Sillen and Kavanagh 1982). Dolomite and

non-volcanic rocks also contain relatively low Sr/Ca values (Odum 1957).

72

In their survey of American rivers and streams, Skougstad and Horr (1960, 1963)

found that areas with high rates of evaporation, low annual rainfall, high salinity and

highly soluble parent material had relatively high Sr concentrations. In general, Sr/Ca

ratios of watercourses remain constant within one major river or lake drainage system

(Sillen and Kavanagh 1982).

Schroeder and colleagues (1972) maintain that intake of foods make up the greatest

contribution of trace elements in humans. However, attesting to the importance of

geology and water sources, in some regions, water may contribute substantial proportions

of certain elements such as Sr, so that water quality is an important determinant of total

Sr intake and hard tissue chemistry (Wolf et al. 1973). Among contemporary Hopi

women, higher levels of bone strontium, compared to their nursing (and food

supplemented) children, has been attributed to greater intake of (relatively high Sr) water

in the form of tea and coffee (Kuhnlein and Calloway 1979).

Overall, the composition of food and water, which is related to local soil geology, is

very much interrelated. Plants growing in soil with relatively high available Sr/Ca ratios

will have generally high Sr/Ca ratios, while soils rich in Ca but deficient in Sr will

produce crops with significantly lower Sr/Ca ratios. Among foods, strontium

concentration (µg/g, or ppm) is most abundant in nuts and spices, followed by seafood,

root and leafy vegetables, legumes, grains, fruit, meat, dairy products, maize and lastly,

fats and oils (Rosenthal 1981; Schroeder et al. 1972) (see Table 4.1).

73

Table 4.1 Average Sr content of various foods (of diverse origin) in order of

relative abundance (with some traditional Maya foods italicized)

(adapted from Schroeder et al. 1972: Table 7)

Food Type Strontium (µg/g) Relative Abundance

Highest

Condiments Cinnamon 118.75

and Dry Spices Allspice 79.17

Cocoa 29.88

Nutmeg 13.90

Nuts Brazil 107.43

Pecan 13.63

Seafood Clam 25.93

Anchovy 16.46

Shrimp 6.18

Sardine (canned) 5.77

Vegetables Kale 117.28

Parsley 6.20

Carrot 2.65

Sweet Potato 1.09

Squash 0.94

Onion 0.65

Tomato 0.48

Green Pepper 0.29

Legumes Dry Lentils 5.07

Lima Bean 4.38

Green Beans 1.09

Red Beans 0.65

Grains Wheat 3.36

Millet 1.29

Barley 0.98

Fruit Strawberry 2.29

Grape 1.72

Banana 0.88

Meat Beef and fat 1.44

Chicken Leg 1.24

Pork Liver 0.76

Chicken Breast 0.52

Dairy Butter (unsalted) 0.80

Milk (whole dairy) 0.50

MAIZE Corn, sweet (fresh) 0.52

Fats and Oils Pork fat 0.14

Corn Oil < 0.10

Lowest

74

Staples such as cereal grains have low Ca contents, but also extremely low Sr values,

resulting in relatively low Sr/Ca ratios (Runia 1987b). According to Rosenthal (1981),

maize is noteworthy because it has “very low” Sr values relative to most foods, even

meat. Data in Table 4.1 reflect this, but both Schroeder and colleagues (1972), and

Rosenthal (1981), who cites their findings, do not specify strontium composition relative

to calcium abundance (Sr/Ca), which is more appropriate for studies of human

metabolism, nutrition and hard tissue incorporation. Additionally, food Sr values are

averaged and derive from different geographical areas, so that diverse geological

conditions, such as soil and water, are not accounted for in the differences.

In contrast, while it is not disputed that maize is low in total mineral content, others

characterize maize as having relatively high Sr/Ca values, like other plants (Burton and

Wright 1995). Compared to 0.52 ppm (Schroeder et al. 1972), Kunhlein and Calloway

(1979) have actually reported a maize strontium concentration of 60 ppm for modern blue

maize from the American Southwest, which is the traditional staple of the Hopi.

Kuhnlein and Calloway (1979) attribute a declining maize dependence to the difference

in tooth dentine between 17th

century Hopi and contemporary individuals, who exhibit

lower Sr values. The extent of the difference is not specified, but bone strontium levels

for the ancient Hopi averaged 478 μg/g (ppm) (Kuhnlein and Calloway 1979).

According to Kuhnlein and Calloway (1979), the high Sr abundance is derived from

dietary components such as blue maize, culinary plant ash (added during maize

processing), local green plants, native salts, as well as the clay of cooking and serving

vessels. Local water from the Colorado River is also notably high in Sr (higher than any

other river in the U.S.), and it is a significant factor determining food levels (Kuhnlein

75

and Calloway 1979). Yet, the strontium abundance cited by Kuhnlein and Calloway

actually refers to ash-processed maize, rather than raw maize. Burton and Wright (1995)

have observed that the Hopi practice of processing maize with saltbush plant ash

(bivilviki) produces a total maize Sr/Ca value that is, in fact, dominated by the Sr/Ca ratio

of the ash source, rather than the maize, which is higher in Sr/Ca. Ash-processed blue

maize consumed by the Hopi has an average Sr/Ca value of 8.48 x 10-3

(Kuhnlein 1981),

which is significantly higher than other known maize values (see Section 4.4).

The overall Sr/Ca ratio of raw maize appears to be relatively high due to its very low

calcium content. Wright (1994) reports on one untreated maize cob from Guatemala with

a Sr/Ca ratio significantly greater than most animal foods in the Maya area (Table 4.2).

Common animals consumed by the ancient Maya include deer, peccary, turkey, water

fowl, turtle, fish, large rodents and various freshwater snails (Emery 1999; Shaw 1991).

Sr/Ca values of some ancient and modern animal samples from Guatemala are

outlined in Table 4.2. Note, however, that Sr/Ca values refer to animal bone and shell

remains, rather than fleshy parts. Lamanai Maya would have consumed the meat of such

animals with a reduced Sr/Ca ratio compared to the hard tissues. In this case, the Sr/Ca

ratio of untreated maize would be enriched compared to animal foods (excluding the

turtle sample analyzed by Wright 1994).

However, when maize is treated with lime to facilitate cooking and consumption, its

Sr/Ca signature is indeed considerably reduced due to an enormous calcium contribution

(see Bressani et al. 2002; Burton and Wright 1995; Wright 1994). The effect of alkali

(lime) processing of maize on total Sr/Ca dietary contribution and hard tissue

composition is discussed in Section 4.7.

76

Table 4.2 Mean Sr/Ca values for common Maya animal and plant foods from the

Pasion region of Guatemala (ratios based on element data in Wright 1994:

Appendix D, E)

Food Item

Mean Sr/Ca (x10-3

)

S.D. (x10-3

)

N

ANCIENT FAUNAL BONE

White-tailed deer (Odocoileus virginianus) 0.551 0.261 3

Brocket deer (Mazama americana) 0.474 - 1

Peccary (Tayassuidae) 0.705 0.256 2

Turtle (Dermatemys) 1.260 0.260 4

Large rodent (Agouti paca) 0.241 - 1

MODERN FAUNAL BONE/SHELL

White-tailed deer (Odocoileus virginianus) 0.800 1.039 2

Brocket deer (Mazama americana) 0.278 - 1

Peccary (Tayassuidae) 0.237 0.200 4

Large rodent (Agouti paca) 0.594 0.695 3

Common turkey (Meleagris gallopavo) 0.154 - 1

Fish (colorada, guapote) 0.933 0.320 3

Freshwater snail (jute) (Pachychilus) 0.465 0.039 2

Freshwater snail (apple) (Pomacea) 0.672 0.301 4

MODERN PLANTS

Corn (Zea mays)

Squash (Cucurbita sp.)

Sweet pepper (Capsicum sp.)

1.129

1.446

0.239

-

-

-

1

1

1

Moving up the food chain, all plants will have lower Sr/Ca and Ba/Ca ratios than

their associated soils because of their tendency to preferentially assimilate calcium over

strontium and barium at the soil/plant interface, which is a process termed

“biopurification” (Elias et al. 1982; Burton et al. 1999).

Besides geological source, strontium values in plants differ significantly between

distinct species due to variations in calcium “biopurification”. In fact, the differences in

both Sr/Ca and Ba/Ca ratios of distinct plant species growing at the same location far

77

exceed (beyond an order of magnitude) the ratio differences among plants of the same

species from different locales (Burton et al. 1999). As stated by Burton and colleagues

(1999: 613), this inter-species variability, despite sharing the same soil conditions, can

exceed the differences due to trophic level biopurification, thus constituting a major

source of variation within a local food web. Still, according to Runia (1987b), it is the

difference in distribution of Sr and Ca that is most significant for plant material, rather

than the degree of discrimination against Sr, which is more relevant for animals including

humans (see below).

Within plants, there are important differences in Sr/Ca ratios between plant parts.

While leaves and shoots will most likely have Sr/Ca ratios resembling those of the soil

solution, plant roots and root crops will have a Sr/Ca ratio 1.5-10 times higher than leaves

or shoots (Runia 1987b: 602). It is thus important to note that the Sr/Ca ratios in specific

products such as cereal grains and roots will differ from the overall plant ratio, which in

this case is lower than the grain and root portions (Runia 1987b).

In mammals, the discrimination of strontium occurs in the digestive system (Kostial

et al. 1969; Lengemann 1963; Spencer et al. 1960; Taylor et al. 1962; Wasserman 1963).

Kidneys also contribute to reduced strontium levels by excreting the element more

rapidly than calcium (Walser and Robinson 1963; Spencer et al. 1960).

As stated above, “biopurification” is the tendency for organisms, both plant and

animal, to preferentially absorb calcium at the expense of other alkaline elements like

strontium and barium, resulting in the increased “purification” of calcium with each step

in a food chain (Elias et al. 1982). This preferential elimination of Sr and Ba relative to

Ca (fractionation) results in a reduction in Sr/Ca and Ba/Ca ratios relative to dietary

78

ratios, which is then reflected in hard tissues. [Comparatively, Ba is slightly more

fractionated than Sr (Elias et al. 1982).] The degree of Sr discrimination from plants to

humans is approximately 0.25% (Brown 1973).

Strontium, like most trace elements, enters the body through food intake and

digestion, distributing into the bloodstream as soluble ions. In older children and adults,

the alimentary tract is the primary site of Sr discrimination and absorption, depending on

relative Ca intake. In the case of developing fetuses and infants, the placenta and

mammary gland will be the main locations of discrimination and absorption (Comar

1963; Comar et al. 1955; Lough et al. 1963).

The overall reduction in Sr/Ca, like Ba/Ca, occurs with ascending trophic position in

the food web. Thus, strontium is more concentrated at the lower plant level, and

decreases, as does the Sr/Ca ratio, as it moves up the food chain through herbivores to

omnivores to carnivores (see Table 4.3).

Table 4.3 Ranges of Sr and Zn content in mammalian bones

(from Rheingold et al. 1983)

Mammal Type

Sr (ppm)

Zn (ppm)

Carnivore

100-300

175-250

(bobcat, wolf, mink, weasel)

Omnivore 150-400 120-200

(rat, beaver, dog, bear)

Herbivore 400-500 90-150

(cattle, deer, goat, rabbit)

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The Sr/Ca ratios of animal tissues, including bone, are lower than their dietary ratios.

Among consumers, herbivores have lower Sr/Ca (and Ba/Ca) ratios than those of the

plants they consume, but higher ratios than other types of animals. Plant Sr/Ca variability

and species-specific consumption of different plants also means that some variation will

also exist within herbivores (Sillen and Lee-Thorp 1994). For instance, leaf-eaters will

exhibit lower Sr/Ca ratios than those herbivores eating high fiber diets (Sillen 1992).

Grazers, and possibly to a lesser extent, browsers, consume plant material with Sr/Ca

ratios that likely resemble Sr/Ca ratios in the reference material (soil and water) Runia

1987b). In general, plant material has approximately three times more strontium than

animal soft tissues (Schroeder et al. 1972). Carnivores will have the lowest Sr/Ca values

of the consumers because, in addition to their digestive system’s discrimination of

consumed Sr, they have ingested tissues that have already discriminated against Sr when

the animal was alive.

An Observed Ratio can be used to quantify the discrimination against strontium (or

differential distribution of Sr) in food chains (Comar et al. 1957). In this case, the

Observed Ratio (OR) = Sr/Ca in sample (e.g., bone/teeth)

Sr/Ca in precursor (e.g., diet)

The OR can be used to express the Sr/Ca relationships between plant/soil, milk/diet

and bone/diet or, essentially, the movement of Sr and Ca through the environment (see

Sillen and Kavanagh 1982). Conversely, the “biopurification” of calcium (discrimination

against strontium) or “discrimination factor” (DF) can be quantified as the inverse of the

OR (Elias et al. 1982; Rosenthal 1981). Notably, the OR values of plants express the

80

relationship between the Sr/Ca ratios in soils and various plant and plant parts (or

differences in the distribution of Sr and Ca in plants), rather than the discrimination

against Sr that is expressed in animal OR’s (Runia 1987b).

Numerous authors have quantified strontium discrimination in actual food chains (see

Sillen and Kavanagh 1982: Table 2). Sr/Ca OR values (bone/diet) for various adult

herbivores and omnivores (e.g., pigs, sheep, mice, cows and dogs, among others) range

from 0.16 to 0.35 (Alexander et al. 1956), but generally measure between 0.20 and 0.30

(Sillen and Kavanagh 1982: 73). Human adults have an average ORbone-diet value of 0.18

(Rivera and Harley 1965).

In their examination of South African food webs, Gilbert, Sealy and Sillen (1994)

clearly demonstrated trophic level fractionation of Sr/Ca. While plants have Sr/Ca values

(not OR) that range from 2.05-41.79 (with 80% in the range of 2.05-10.26), herbivore

bones exhibit ratios between 0.96-5.52, and carnivores from 0.39-2.31 (Gilbert et al.

1994: Table 1). Sr/Ca and Ba/Ca values for herbivores and carnivores overlap

considerably and both exhibit greater reduction in Ba/Ca than Sr/Ca because mammals

discriminate against Ba more than Sr (Elias et al. 1982). In general, their Sr/Ca ranges

are consistent with plant/consumer differences in other studies of the same region (Sealy

and Sillen 1988; Sillen 1992).

Similarly, Elias and colleagues (1982) found a four-fold reduction in Sr/Ca from

sedge leaves to voles, which concurs with findings in Sillen and Kavanagh’s (1982: Table

2) survey. Increased fractionation took the form of a further six-fold reduction in Sr/Ca

from voles to predating pine martens (Elias et al. 1982). Comparable data includes

81

Burton and colleagues’ (1999) 80% reduction in Sr/Ca for a bobcat/hare predator-prey

pair, as well as other findings by Price (1985) and Price, Smick and Chase (1986).

In light of the Sr/Ca distinctions between different foods and types of consumers, one

usefulness of Sr in paleodietary reconstruction concerns dietary regimens. Toots and

Voorhies (1965) were the first researchers to test this by differentiating bone Sr/Ca

between Pliocene herbivores and carnivores. Skeletons of individuals ingesting large

quantities of meat are expected to contain relatively low levels of Sr, while those relying

on a greater percentage of vegetable foods should exhibit higher Sr/Ca ratios (Brown

1973, 1974; Fuchs 1978; Gilbert 1975; Pate & Brown 1985; Price & Kavanagh 1982;

Schoeninger 1979a, 1981, 1982, 1985; Sealy & Sillen 1988; Sillen 1981a, 1986; Sillen

and Kavanagh 1982; Szpunar 1977). Brown (1973, 1974) has found that in herbivorous

humans, the average Sr/Ca ratio is around 1:2000, while meat-eating humans display a

mean ratio of 1:4800.

Seafood has been thought to concentrate much more strontium than terrestrial

resources due to high seawater strontium levels. Strontium is the most abundant trace

element in seawater, averaging 8 ppm (Schroeder et al. 1972). High Sr levels are

correlated with water salinity (Odum 1951), depth and temperature (Angino et al. 1966;

see White 1986). The abundance of Sr in seafood is due to compounds in shell such as

aragonite and strontianite, which accumulate Sr rather than maintain a maximum

threshold reflecting surrounding seawater (Schoeninger and Peebles 1981).

Given that there is high strontium concentration in seawater, and assuming that the

intake of similarly Sr-enriched marine foods would elevate tissue levels in consumers,

numerous researchers have examined human hard tissue Sr to assess the proportion of

82

seafood intake (Benfer 1984; Burton and Price 1990; Connor and Slaughter 1984; Gilbert

et al. 1994; Schoeninger and Peebles 1981; Sealy and Sillen 1988).

Nonetheless, while seawater is high in Sr, like terrestrial food webs, it decreases

(“biopurifies”) with increasing trophic position in the marine environment, so that marine

diets are not equally high in Sr (Burton and Price 1999). As Burton and Price (1999:

235) note, even humans consuming significant quantities of marine mammals and fish are

still eating large amounts of meat, which can be expected to have lower, rather than

elevated, Sr/Ca values, that are comparable to terrestrial omnivores and carnivores.

Consumption of seafood (including mollusks and crustaceans) has an insignificant

effect on human tissues because, like mammals, very little Sr and Ca concentrates in

edible portions of seafood, with most alkaline earth metals contained in hard tissues.

Strontium content in the soft tissues of fish and marine gastropods represent only

approximately 0.1% of the total Sr in marine tissues (Sillen and Kavanagh 1982: 79). (In

contrast, barium is very low in seawater, averaging 0.006 ppm compared to strontium’s 8

ppm [Schroeder et al. 1972]. Because it is absorbed at one-fifth the rate of Sr [Marcus

and Wasserman 1965], the Ba/Ca ratio of marine foods [flesh and hard tissues] is even

further reduced compared to Sr/Ca.)

As Burton and Price (1999) insist, hard tissue Sr/Ca is not a sensitive indicator of

marine resource consumption and cannot be used to differentiate between marine and

terrestrial diets. However, as it faithfully represents marine foods as a meat source, the

assertion that “bone strontium meaningfully tracks dietary Sr/Ca ratios” (Burton and

Price 1999: 235) is further strengthened.

83

4.2 The Role of Strontium in Human Nutrition

As stated above, strontium is considered a non-essential trace element in human and

animal nutrition. The definition of “essentiality” is based on an element’s influence on

“important physiological functions”, but in cases where the deficiency of an element is

not widely associated with unequivocal functional impairment (detrimental effects), its

nutritional necessity is less clear. Despite being non-essential, strontium’s metabolic role

in animals and humans can be demonstrated by the various abnormalities that develop in

its absence. For instance, in experimental animals, withholding of strontium from a

purified diet results in reduced hard tissue calcification and slowed growth rates (Rygh

1949).

Additionally, because it can substitute for calcium in calcium-deficient areas of

apatite crystals, strontium supplementation has been found to reduce the rate of bone loss

and increase bone density (re-mineralization) (McCaslin and Janes 1959, 1981; Shorr and

Carter 1952; among others). It may also act as a cariostatic agent for teeth, resulting in

lower caries incidence in areas of high strontium levels in drinking water, soil and foods

(see Curzon 1983).

The replacement or substitution of Ca by Sr entails changes in physical and chemical

properties of enamel apatites (Curzon 1983; Featherstone and Nelson 1980). For

instance, LeGeros and colleagues (1976) found that the presence of Sr limits the

incorporation of carbonate. Carbonate affects apatite structure, increases apatite

reactivity to acid, and has been associated with enamel crystal defects, dislocations and

increased solubility and dissolution (Curzon and Featherstone 1983; Cutress 1972;

Dedhiya et al. 1974; Featherstone et al. 1981; Nelson 1981).

84

Strontium substitution is thought to reduce enamel dissolution and caries incidence,

either by increasing the size and surface area of apatite crystals, or by reducing carbonate

incorporation (Curzon 1983: 299). In total, strontium can function very similarly to

calcium. Accordingly, strontium can be considered important (though not essential) for

human nutrition since its deficiency does result in some degree of sub-optimal biological

function, which can be prevented and reversed by its restoration to the body.

4.3 Strontium Absorption and Hard Tissue Incorporation

Strontium has a vital relationship to calcium in that its absorption and incorporation

in hard tissues are dependent on the concentration and availability of calcium in the body.

Increased intake of dietary calcium will reduce the level of strontium absorption and

retention (and Sr/Ca ratio), while reduced available calcium will result in greater uptake

of strontium (Thompson 1963). This discrimination against strontium exists because of

the relatively lower absorption rate, but higher urinary excretion, of strontium compared

with calcium (Curzon 1983). Since calcium is an essential nutrient, it is tightly regulated

in the body, with its absorption dependent on the balance between blood and extracellular

fluid calcium levels. Comparatively, calcium, strontium and barium are absorbed at a

ratio of 10:5:1 (Marcus and Wasserman 1965). [As a result, while Sr/Ca is reduced at

higher trophic levels in a food web, Ba/Ca is even further reduced (Elias et al. 1982).]

As outlined by Sillen and Kavanagh (1982), the mechanisms of absorption of Sr and

Ca are both qualitatively and quantitatively similar. For instance, strontium is bound by

calcium-binding proteins necessary for the transfer of calcium across intestinal

85

membranes, but this protein has a higher affinity for calcium than for strontium (Ingersoll

and Wasserman 1971; Menczel and Mor 1972; Wasserman 1963).

Besides calcium content, strontium absorption is also affected by all the factors that

influence calcium absorption, namely vitamin D, age and metabolic status (Sillen and

Kavanagh 1982). Comparatively, because calcium is an essential nutrient, but strontium

has no known independent metabolic function, normal adults absorb 40-80% of ingested

Ca, but only 20-40% of ingested Sr (Spencer et al. 1960, 1973). Estimates for Sr

absorption among animals are even as low as less than 10% of ingested Sr (Elias et al.

1982; Wasserman 1963).

The average adult diet generally provides 1 to 3 mg Sr/day, but the total intake is also

dependent on water quality and strontium content (Schroeder et al. 1972). As well,

differences in Sr intake can be related to animal milk consumption. In populations that

consume animal milk beyond childhood, the average Sr intake is approximately 1.4 mg

Sr/g Ca (Sr/Ca ratio of 1.4 x 10-3

) per day, while those who do not consume animal milk,

and who rely on grains as a staple, can average 2.7 – 4.9 mg Sr/g Ca (Sr/Ca ratio of 2.7 -

4.9 x 10-3

) (Rosenthal 1981). For instance, higher Sr/Ca values in the hard tissues of

individuals from East Asia have been attributed to lower calcium intake from milk

avoidance (after childhood) (Schroeder et al. 1972). While American children and adults

average 96 ppm and 110 ppm in bone strontium, respectively, Asian children and adults

have bone Sr values averaging 320 ppm and 190 ppm (Schroeder et al. 1972).

Among adults, providing that calcium levels remain within normal physiological

limits, the relative absorption of Sr and Ca does not vary a great deal (Wasserman and

Comar 1960; Spencer et al. 1961; Wasserman 1963) (but see below for variations in

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absorption due to age, sex and other factors). As a result, Sillen and Kavanagh (1982)

maintain that medium or high levels of calcium in the diet are unlikely to have a

significant effect on the applicability of Sr/Ca analysis to paleodietary reconstruction,

since the discrimination against Sr is generally unaffected. However, they warn that it

should not be used in cases where extreme calcium deprivation is suspected.

While the majority of dietary strontium is excreted renally, or during lactation and

placental transfer among women, a small amount of strontium is circulated in the

bloodstream for eventual hard tissue incorporation. In erupted teeth, in vivo exchange of

elements primarily occurs in dentine via the pulp cavity blood supply, but saliva also acts

as a medium for element exchange in enamel.

Alkaline earth elements such as strontium and calcium are notable calcified tissue

seekers, with most strontium incorporating into the hydroxyapatite fraction of bones and

teeth after absorption (Boyde et al. 1958). In fact, strontium and calcium are deposited in

calcified tissues in greater quantities than most other trace elements (Turekian and Kulp

1956). In humans, approximately 99% of body Sr and Ca is stored in hard and

connective tissues (Avioli 1988; Elias et al. 1982; Schroeder et al. 1972). In enamel,

strontium is primarily incorporated during the maturation phase.

Strontium incorporates into bone and dental apatite by replacing calcium ions. This

is the case for all divalent cations, i.e., Ca, Sr, Mg, Ba, Pb and Zn. In life, Sr2+

is

incorporated in bone as an isovalent replacement for Ca2+

. Up to four of the Ca ions in

human enamel apatite can be replaced by Sr. This can be attributed to strontium’s close

similarity to calcium in chemical and physical properties, most notably electron

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configuration, ionization energy and ionic size (Sr = 0.112 nm; Ca = 0.099 nm) (Curzon

1983: 296; Schoeninger 1979a).

As stated above, the incorporation of Sr in apatite crystals results in some structural

modification. In synthetic hydroxyapatite, the addition of Sr can increase the size of

each crystallite (LeGeros et al. 1977) and limit carbonate incorporation (Curzon 1983;

LeGeros et al. 1976). Fortunately, a small amount of strontium exchange for calcium

does not adversely affect apatite formation or calcification, but large amounts may inhibit

calcification and have been shown to produce “strontium rickets” in experimental

animals (Storey 1961); dentine hypomineralization and enamel hypoplasia in rats

(Curzon 1983); and enamel mottling in humans (Curzon and Spector 1977).

Importantly, strontium levels in hard tissues are not directly proportional to the

amount of strontium in the diet, but rather, to the mean Sr/Ca ratio of the diet (Burton and

Wright 1995). With preferential calcium absorption, the amount of strontium absorbed

and retained in hard tissues is only approximately 20% that of calcium (Elias et al. 1982).

At each trophic level, hard tissue Sr/Ca will drop to approximately one-fifth of the dietary

Sr/Ca value (Elias et al. 1982). As summarized by Burton and Wright (1995: 274):

(Sr/Ca)hard tissues (0.2)(Sr/Ca)diet

As previously stated, knowledge of the total Ca contribution to a diet is essential.

The dependence of Sr on Ca intake means that high calcium foods will have a

disproportionately large effect on hard tissue Sr/Ca, while low Ca intake will have a

negligible, or even reverse, effect on hard tissue Sr/Ca ratios (Burton and Wright 1995:

275). Consequently, high intake of maize enriched with Ca from alkali treatment, which

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lowers the Sr/Ca ratio, has a potentially significant effect on hard tissue composition (see

Chapter Eight).

4.4 Variations in Strontium Absorption

Studies of enamel strontium content indicate wide disparities in concentration, with

values as low as 13 ppm, to as high as 1400 ppm, in permanent teeth from dissimilar

geographic regions and time periods (see Curzon 1983: Table 15-6; Curzon and

Featherstone 1983: Table 3; Curzon and Losee 1977; Lane and Peach 1997: Table 2;

Losee et al. 1971; Wolf et al. 1973). In a survey of 24 countries around the world,

Thurber and colleagues (1958) found means that ranged from 101-344 ppm, while

Turekian and Kulp’s (1956) investigation of contemporary skeletons from 14 countries

gave values between 40 and 740 ppm. Comparisons of bone Sr between various regions

of the United Kingdom gave an overall coefficient of variation of 32.8%, ranging from

21.6 - 47.8% variation within counties (see Sillen and Kavanagh 1982: Table 5).

Such variation can be attributed to various factors, namely: distinct geology (water,

food sources); diverse analytical methods (spectrography, neutron activation, X-ray

emission, mass spectrometry, optical emission, atomic absorption); sample size variation;

different developmental and temporal ages of hard tissue samples; and variable caries

prevalence (which can reflect different Sr levels of the environment and tooth).

Within teeth, Steadman and authors (1958) have found a consistent distribution of Sr

across the total depth of enamel, but most evidence indicates that there are recognizable

variations in Sr/Ca between different enamel layers, most notably in the surface layer of

permanent teeth (Curzon 1983). (Similarly, slight Sr variation has been found between

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different bone types such as cancellous ribs and cortical bone within the same individual

[Tanaka et al. 1981]. This variation, which corresponds with age-related differences, has

been associated with metabolic rates, but in archaeological samples, it is also possible

that diagenesis is accounting for some variation, as cortical bone is more stable and

resistant to post-mortem degradation than cancellous bone [see White 1986].)

In enamel, Little and Barrett (1976) have found a decreasing gradient of strontium

concentration from the surface inward, which suggested surface enamel incorporation of

strontium from the oral environment after tooth eruption. When they examined caries

rate, they found that teeth from areas of high caries prevalence had less surface enamel

strontium than teeth from low caries regions, which had at least twice as much strontium

(and fluoride) in surface enamel. Curzon (1983) has noted, however, that the variation in

enamel strontium and caries indices within groups is too large to ascertain a clear

relationship, as Spector and Curzon (1979) actually found no significant relationship

between surface enamel strontium and individual caries prevalence.

Conversely, Sr demineralization has also been observed in surface enamel, resulting

in increased Sr concentration toward the enamel-dentine junction (Reitznerová et al.

2000). According to Reitznerová and colleagues (2000), it is likely that pH changes in

the oral environment are responsible.

Between the two dentitions, it has been postulated that there might be higher trace

element levels in permanent enamel compared to deciduous enamel (Vrbič et al. 1987).

This was based on the fact that while some trace elements are bound to the mineral

structure or organic matrix of enamel during enamel formation, other elements are

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adsorbed on the enamel surface later in life, i.e., post-development, which would give

permanent enamel more time to acquire (surface) elements.

Vrbič and co-workers (1987) found that of eight elements measured, three (Cd, Cu,

V) were actually higher in deciduous enamel, but five (Al, Ba, Li, Mo and Sr) occurred in

higher concentrations in permanent enamel, although only Ba (p<0.01), Li (p<0.01) and

Sr (p<0.02) were highly significant. In this study, average Sr concentration in primary

teeth was 74.2 μg/g (ppm), while the mean value for permanent teeth was 106.7 μg/g

(Vrbič et al. 1987: Table II). However, these results are absolute strontium values, rather

than relative Sr/Ca ratios, which are more relevant for comparison. In addition, a search

of the literature failed to uncover other findings or supporting evidence.

Variations aside, strontium concentration commonly ranges from 100-200 ppm in

enamel (Brudevold & Steadman 1956), or 111 ppm on average (Carlson 1990: Table 1),

150-250 ppm in bone ash (Aufderheide 1989), and 100-600 ppm in dentine (Rowles

1967), or 94 ppm on average (Carlson 1990: Table 1).

Within such ranges, strontium absorption differs by age, sex and reproductive status.

The most important metabolic factor affecting absorption of alkaline earth metals in

animals is developmental age, since discrimination and relative absorption of such

minerals is dependent on gastrointestinal capacity (maturation). For instance, Sowden

and Stitch (1957) found that average strontium abundance in nursing infants was 79.1 +

20 μg/g (ppm), which increased regularly with age, reaching 114 + 28 μg/g in adults.

Bedford et al. (1960) and Schroeder and colleagues (1972) have also observed the same

positive trend with age.

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However, the evidence has not been consistent, with some studies finding higher

Sr/Ca in children compared to adults (Brown 1973; Lengemann 1963; Lough et al. 1963);

and others reporting no significant age difference except in fetal bone (Szpunar 1977;

Turekian and Kulp 1956). It is believed that factors mentioned previously are responsible

for the inconsistency of findings, i.e., differences in geology, preservation, analytical

method, sample size, age categories and caries prevalence.

In the total human lifespan, average bone strontium levels generally decrease with

age (Curzon and Featherstone 1983). This general pattern is characterized by several

notable fluctuations however. Among children, there are age-related variations in Sr/Ca

enamel composition due to dietary changes that are significant. For this study, in

particular, the variation in strontium concentration prior to age-related decline is the

premise from which infant dietary behavior will be based.

Early life is characterized by relatively low Sr/Ca levels, with newborn infants

generally having the lowest Sr/Ca ratios in a population due to placental discrimination of

Sr during fetal development (Comar 1963; Comar et al. 1955, 1957; Spencer et al. 1956).

Compared to mothers’ tissues, fetal hard tissues are approximately half the Sr/Ca

concentration (Comar 1963). In their examination of maternal and stillborn skeletons,

Knizhnikov and Marei (1967) found that the observed ratio (OR) of infant bone Sr/Ca to

maternal diet Sr/Ca was only 0.08, while the OR of maternal bone Sr/Ca to maternal diet

was 0.20, which was in the normal adult range (Sillen and Kavanagh 1982). Similarly,

Beninson and colleagues (1964) found an adult OR (maternal bone/maternal diet) of 0.23,

while the stillborn OR (stillborn bone/maternal diet) was only 0.013 for Sr/Ca. Results

by Sowden and Stitch (1957) also reveal low Sr content in infant hard tissues.

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However, young animals actually consistently exhibit less discrimination against

strontium than adult animals (see Sillen and Kavanagh 1982: Table 3). This is due to the

higher absorptive efficiency of alkaline earths in young animals, or rather, reduced

discrimination (less urinary excretion) of Sr by immature digestive systems. Newborns

and infants up to 9 months of age are observed to have bone Sr/Ca comparable to their

diet (OR ~ 1.00) (Lough et al. 1963; Rivera and Harley 1965; Straub et al. 1961).

Alkaline elements present in milk are absorbed at a higher rate than those of other

foods since such elements are more completely absorbed from liquids than solid foods

(Marcus and Lengemann 1962). The absorption of Sr from milk increases proportionally

to Ca due to an enhancement produced by lactose (Lengemann 1963). Vitamin D and the

amino acids lysine and arginine also act to increase Sr absorption in milk (Comar et al.

1957).

While relative Sr absorption may be higher in infants, the absolute amounts of Sr

available to infants and young animals are significantly lower than the average adult diet,

since milk is exceptionally low in Sr due to mammary gland discrimination (Lough et al.

1963; Twardock 1963). Indeed, compared to calcium, the transfer of strontium from

blood to milk is 10-14 times less (Comar et al. 1961; Wasserman et al. 1958). Unlike the

relatively high Ca content of human milk, Sr values range between 0.14-0.35 mg Sr/g Ca

(Rehnberg et al. 1969; Rosenthal 1981), or a breast milk Sr/Ca ratio of 0.14 - 0.35 x 10-3

.

Exclusively breastfed infants display the lowest Sr/Ca values until they are

supplemented with non-breast milk foods and liquids (e.g., cereal gruels), which have

significantly higher Sr/Ca abundance (see Chapter Five). For instance, Central American

corn is reported to have Sr/Ca values of 1.13 x 10-3

(Wright 1994) and 2.51 x 10-3

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(LaVigne 2002), while some North American corn even reaches 7.14 x 10-3

(Shacklette

1980; Watt and Merrill 1963) and 8.48 x 10-3

(Kuhnlein 1981), which is likely due to

processing techniques (see Section 4.1). Increased food supplementation and decreased

breast milk intake is postulated to increase the level of Sr/Ca in infant hard tissues

developing at the time, in effect tracking the process of weaning (see Mays 2003; Sillen

and Kavanagh 1982).

In their study, Bryan and Loutit (1964) found that British infants from birth to six

months of age had a mean bone value of 0.2 mg Sr/g Ca, or a Sr/Ca ratio of 0.2 x 10-3

.

After six months of age, when infants began food supplementation, bone Sr/Ca rose

steeply and continued to increase slowly thereafter until adulthood, when bone values

average around 0.33 mg Sr/g Ca (Sr/Ca of 0.33 x 10-3

).

Despite maturation of the gastrointestinal tract after the first year of life (Sillen and

Kavanagh 1982), and a concomitant increase in the discrimination of Sr, higher food

strontium intake still results in rising levels of Sr. Thus, while infant hard tissue strontium

is primarily influenced by diet, i.e., breast milk and eventual solid food intake, after the

first birthday, gastrointestinal maturation (discrimination) plays an important role in

variations in hard tissue Sr/Ca. By about 8-10 years of age, with fully mature

gastrointestinal systems and improved Sr discrimination, reduced subadult Sr/Ca values

generally resemble those of adults (Rivera and Harley 1965). However, strontium levels

are the most varied in children, particularly between the ages of 4 and 13 (Lambert et al.

1979; Sillen and Kavanagh 1982). High values also at adolescence reflect peak periods

of metabolic activity (Lambert et al. 1979; Loutit 1967).

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Thereafter, strontium levels among adults will stabilize between the ages of twenty

and fifty years (Lambert et al. 1979). In later adulthood, reduced gastrointestinal

discrimination (rather than dietary changes) results in slightly increasing strontium

values, although not to the extent of subadults. For instance, Hodges and colleagues

(1950) found that adult cadavers 42-75 years of age had bone strontium values averaging

around 0.59 mg Sr/g Ca (Sr/Ca ratio of 0.59 x 10-3

).

Since strontium variability in bones of children and adolescents is greater than among

adults, Sillen and Kavanagh (1982) have insisted that bone strontium should only be

compared between adults. However, this variability in children, when applied to dental

chemical analysis, provides a vital comparative tool for nutritional research. As a

permanent record of elemental incorporation during crown development in childhood,

such variation is highly useful to assess differences in infant nutrition between

individuals of a population through time and space.

In terms of variation due to sex, the results do not entirely agree. Lambert and co-

workers (1979) have found significantly higher Sr levels among males, but Price and

colleagues (1986) have observed the opposite, with females having higher strontium

levels, which were partly attributed to reproductive status (see below).

The hard tissue Sr/Ca values of modern western populations do not reflect significant

differences between adult males and females (Turekian and Kulp 1956b), but Sillen and

Kavanagh (1982) note that this equality might not characterize prehistoric populations. In

contrast to contemporary western women, in ancient times, it is expected that relatively

more women were either pregnant or lactating for most of their adult lives (Sillen and

Kavanagh 1982). Many studies, of both modern and ancient skeletons, have reported

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relatively higher Sr/Ca levels in the bones of adult females compared to males (Blakely

1989; Brown 1973; Gilbert 1975; Lambert et al. 1979; Price and Kavanagh 1982;

Schroeder et al. 1972; Sillen 1981a; Vuorinen et al. 1996).

Higher levels of hard tissue strontium in women are related to metabolic changes

during pregnancy and lactation. Numerous studies indicate that pregnancy increases the

absorption of all alkaline earths, most notably calcium (Allen 1998; Allen et al. 1994;

Hayslip et al. 1989; Heaney and Skillman 1971; Kostial et al. 1969; Ritchie et al. 1998;

among others). Maternal calcium levels are particularly lowered during pregnancy

because of fetal development demands. Despite continued discrimination against

strontium by the placenta and mammary gland, a slightly reduced discrimination with

pregnancy entails a significant net increase in the Sr/Ca ratio of maternal plasma, and

ultimately, hard tissues (Kostial et al. 1969; Blanusa et al. 1970).

Physiological differences in hard tissue Sr/Ca due to pregnancy and lactation

obviously have ramifications for status distinctions in archaeological populations.

Several studies associate relatively high bone strontium (inferring high plant intake) with

“low status” individuals, while more privileged individuals have lower strontium values

that are attributed to greater access to meat resources (Brown 1973; Gilbert 1975;

Lambert et al. 1979; Price and Kavanagh 1982; Schoeninger 1979a,b; Sillen 1981; White

1986; White and Schwarcz 1989; Wolfsperger 1993).

For instance, at Chalcatzingo, Mexico, high status individuals (as determined by

grave associations such as ceramics, ground stone, figurines, jade) were found to have the

lowest mean bone strontium levels, which were associated with less reliance on maize,

and greater access to meat protein (Schoeninger 1979). In contrast, lower status

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individuals, in poorly furnished graves, provided very high mean bone strontium values,

which was associated with greater reliance on plant foods such as maize.

However, in light of better understanding of strontium and calcium metabolism and

hard tissue incorporation, as well as the effects of alkali processing on maize Sr/Ca

values (see Section 4.7), this status association needs re-examination. According to

Burton and Wright (1995), the calcium-rich lime used to process maize results in

extremely low Sr/Ca maize products (gruel, masa, tortillas) that are indistinguishable

from other low Sr/Ca foods such as meat.

This explains the supposed “discrepancy” in Tipu Maya bones found by Bennett

(1986), who assumed that high maize intake should entail high bone Sr/Ca. In that case,

while carbon isotopic data inferred high maize intake (between 65-75% of total diet), this

seemingly did not correspond with the low Sr/Ca content of bones. Presently, this can be

explained by the high Ca content of lime-treated maize ingested by Tipu Maya.

Similarly, White (1986) found that Lamanai females with relatively low bone Sr

levels had supporting (high) Mg values that pointed to greater maize intake, contrasting

the traditional high Sr-high maize association. Relatively low levels of bone zinc also

suggest reduced meat (and seafood) consumption among Lamanai women (White 1986).

At Lamanai, differences in strontium values were also interpreted by White and

Schwarcz (1989) to reflect status distinctions in meat intake. In this case, elite Early

Classic tomb individuals (male and female) exhibited significantly higher strontium

concentrations than non-tomb individuals (White 1986; White and Schwarcz 1989).

Together with isotopic data (15

N and 13

C values), the authors attributed these patterns

in hard tissue chemistry to greater elite consumption of imported reef-marine foods, but

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reduced consumption of more “ordinary”, locally-produced, maize, compared to non-

elites. Furthermore, differences in isotopic 15

N values between male and female elites

suggest that elite males exhibit even greater distinction, with the greatest access to

imported foodstuffs (White and Schwarcz 1989).

Yet, despite the high strontium content of seawater and marine animal hard tissues, it

is the soft tissues of such seafood that are consumed, which are, like meat, notably low in

Sr/Ca (see Burton and Price 1999). In this case, marine foods should be indistinguishable

from terrestrial meat and cannot be inferred by hard tissue Sr/Ca.

In light of sex differences, it is possible that, in other cases, individuals of lower

socioeconomic status may have actually been females who had children, in which case,

metabolic factors, rather than status-related dietary access, are responsible for higher

Sr/Ca values (Sillen and Kavanagh 1982). Still, females are often accorded lower

socioeconomic status (and less access to high-protein status foods such as meat) than men

in archaeological populations, so that the association of high Sr/Ca values (high plant

intake) with low social status is not entirely incorrect.

Clearly, any assessment of status associations with Sr/Ca values in hard tissues must

be evaluated in light of the sex of each individual. Higher female strontium levels may

be due to differential food (meat vs. plant) intake, but pregnancy and lactation also

influence relative Sr absorption and hard tissue incorporation. Further, if maize is the

major staple of the population, as it is for the ancient Maya, then the relatively reduced

Sr/Ca ratio of lime-processed maize must be considered (see Section 4.7). Finally,

attributing sex or status factors to distinctions in dietary intake and hard tissue Sr/Ca must

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also rely on comparative isotopic (e.g., carbon) evidence, as well as archaeological

context (e.g., burial assemblage).

4.5 The Applicability of Strontium in Hard Tissue Paleodietary Analysis

In recognition of the myriad factors affecting hard tissue chemistry, a number of

criteria have been amassed to determine the appropriateness of an element for

paleodietary research (see Beck 1985; Ezzo 1994; Gilbert 1977; Gilbert and Mielke 1985;

Parker and Toots 1980; Price 1989; Sandford 1993; among others). These limiting

characteristics include:

1) The element must be hard tissue-seeking, i.e., it concentrates in hard tissues and is

incorporated into the hydroxyapatite crystal, rather than remain surface-bound on the

crystal

2) There must be documentation of a direct relationship between the levels of an element in

the diet and the levels present in human skeletal tissue. Moreover, the element values in

different food types should be distinguishable by trophic level (biopurification), or some

other distinction (e.g., tissue-specific occurrence)

3) The element levels in the skeletal tissue must be adequate to allow for accurate and

consistent measurement and such levels should be most diagnostic of an expected range of

consumption

4) The element preferably should not be an essential nutrient, so that it is not under tight

homeostatic regulation (since this feature of essential nutrients means they are largely

non-fluctuating)

5) The element should mimic the activity of a hard tissue-seeking essential element (e.g., Ca)

in biological systems

6) Concentrations of an element in human hard tissues either should be unaffected by

disease, or the diseases which alter the concentration should be identifiable in skeletal

remains

7) Concentrations of an element in human tissues should not be subject to significant

diagenetic change, either by leaching or enrichment, during extended periods of interment

8) Such elements have the potential to test nutritional problems using other skeletal

indicators

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As stated by Ezzo (1994: 8), and also applicable to dental hard tissues,

…for an element to be a valid paleodietary indicator it should be incorporated into the

structure of bone hydroxyapatite at levels that are proportionate to levels in the diet, it

should not be an essential nutrient or one subject to metabolic regulation, and it should

be present in bone at levels that exceed contributions likely to occur as a result of

postdepositional processes.

On the whole, strontium, barium, zinc and magnesium have been the most widely

examined elements in paleodietary research due to their sensitivity to dietary intake and

post-mortem stability in human hard tissues. However, according to many researchers

(Beck 1985; Brown 1973; Burton and Price 1990; Klepinger 1993; Lambert et al. 1979,

1982, 1985, 1990; Price et al., 1985, 1986, 1992; Radosevich 1993; Sandford 1993;

Schoeninger 1979; Sealy and Sillen 1988; Sillen 1992; Sillen and Kavanagh 1982; Toots

and Voorhies 1965, among others), only strontium and zinc meet all the necessary

requirements and can be considered the most appropriate elements for paleodietary

reconstruction. In part, increased understanding of the effects of diagenesis on hard

tissue chemistry has significantly altered the perception that all dietary elements can be

used to infer diet.

Notably, however, Ezzo (1994) feels that only strontium and barium are valid

elements for hard tissue paleodietary research. Zinc should be excluded because 1)

changes in zinc intake of adults do not significantly correspond with relative zinc levels

in bone; and 2) there is no well-founded physiological or biochemical model for its

incorporation in hard tissues (Ezzo 1994).

Unlike many other elements, there is clear understanding of the complex nature of

strontium metabolism, particularly the realization that its eventual makeup in hard tissues

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is a result of diet, age and health status, as well as post-depositional factors.

Distinctively, strontium has been extensively studied with respect to 1) its varied

distribution in food chains; 2) its physiological basis in human and animal nutrition,

particularly regarding discrimination; 3) the nature of in vivo hard tissue incorporation; 4)

its post-mortem stability/diagenetic alteration in hard tissues; and, importantly, 5) clear

demonstration that its variation in dietary components corresponds with variations in hard

tissue composition.

4.6 Strontium Preservation in Fossilized Hard Tissues

Since paleodietary reconstruction relies on fossilized human hard tissues, the

compositional integrity of such tissues in the post-mortem environment is a principal

consideration. Fortunately, the use of strontium in bone and dental chemical analysis is

fully warranted. Overwhelming evidence from studies of both hard tissue indicators of

diet and hard tissue diagenesis indicate that Sr/Ca in fossilized human hard tissues is a

faithful reflection of in vivo incorporation (Burton and Price 1999; Ezzo 1994; Lambert et

al. 1985; Pate and Brown 1985; Schoeninger 1979b; Sillen and Kavanagh 1982; White

1986; among others). Strontium’s post-mortem chemical stability is attributed to its very

stable 2+ cation position in apatite mineral, which is typical of all alkaline earth metals,

including calcium, barium and magnesium.

Still, there has been some conflicting evidence as to its post-mortem integrity in

human hard tissues, most notably bone. While generally stable, strontium values in fossil

bone can be depleted or enriched by mineral dissolution of the hydroxyapatite structure.

This can occur by microbial decomposition of collagen, and consequent weathering by

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organic and carbonic acids formed by the decomposition (Pate & Brown 1985: 488). In

addition, acidic soil conditions can result in the replacement of surface bone Ca by soil

Sr, Mg and Zn, resulting in their enrichment in bone (Lambert et al. 1985b).

The strontium content of fossil bones and teeth is usually higher than the strontium

levels of surrounding sediment matrix (Wyckoff and Doberenz 1968), although this is

expected because of primary enrichment in living tissues from dietary and water intake,

and similarly high calcium content of fossils (Sillen and Kavanagh 1982).

During fossilization, almost all minor and trace elements are enriched, rather than

depleted (Carlson 1990: 545). This is in contrast to major elements (e.g., calcium and

phosphorus), which generally remain stable post-mortem, although carbonate has been

found to deplete slightly (Fosse et al. 1981; Puech et al. 1986).

Parker & Toots (1970, 1974, 1980) have maintained that human hard tissues are not

subject to diagenetic strontium addition. Their analyses of bone, dentine and enamel

from fossil Subhyracodon indicate consistent, equal amounts of strontium, while sodium

concentrations are lower (due to leaching/diagenetic loss), and fluorine concentrations are

higher (due to diagenetic enrichment) in bone and dentine relative to enamel.

However, Sillen and Kavanagh (1982) challenge this interpretation of the stability of

strontium in fossilized hard tissues. They suggest that the equal strontium levels between

bone, dentine and enamel actually reflect chemical equilibrium of the remains with the

post-mortem environment. Firstly, strontium from adult bone and tooth enamel can not

be compared because enamel is not remodeled in adulthood, as is bone, and therefore

reflects circulating element levels of the young animal, while bone reflects adult

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circulating levels. Regardless of dietary stability, metabolic differences between young

individuals and adults should reflect different elemental levels.

Strontium contamination has also been found in human skeletons from freshwater

and coastal shell middens (the source of contaminating Sr), which were in concentrations

much higher than would be expected for normal reliance on seafood (Gilbert et al. 1994;

Kyle 1986; Schoeninger and Peebles 1981; Sealy and Sillen 1988). In addition, Sr

diagenesis is evident in fossils from Hayonim Cave, Israel, which failed to exhibit Sr

distinctions associated with fossil herbivore, carnivore and human omnivore remains

(Sillen 1981b).

Fortunately, the minimal evidence of diagenetic alteration of strontium has been

restricted to fossil bones, rather than teeth. Strontium is consistently observed to retain

its biogenic concentration and isotope ratio in enamel tissue, unlike dentine, which has

even been shown to undergo complete turnover of original biogenic Sr (Budd et al.

2000). Almost certainly, this fact renders the analysis of strontium in dental enamel the

most reliable method to reconstruct ancient diet and nutrition from human remains.

4.7 The Effects of Maize Processing on Hard Tissue Sr/Ca Composition

In examining maize’s Sr/Ca imprint in hard tissues, one must consider the

“paradoxical effect” of maize, or the nature of hard tissue Sr/Ca to change in a direction

contrary to that of the increasing maize component, due to low mineral content (Burton

and Wright 1995). Increased intake of lime-treated maize decreases the relative

contribution of other dietary components, but calcium abundance in the enriched maize

dampens the total Sr/Ca ratio so that it mistakenly appears like some other (low Sr/Ca)

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foodstuff is increasing instead of maize (Katzenberg 1984; Burton and Wright 1995). In

total, high calcium foods will have a disproportionately large effect on hard tissue Sr/Ca

(Burton and Wright 1995).

To shed light on the nature of Sr/Ca patterns in Lamanai enamel, the dietary diversity

and food processing techniques of ancient Maya need to be assessed. Like most

populations in the New World, the Maya relied on maize as a dietary staple. However,

untreated, dried, ripe maize has marginal nutritional value, particularly in the essential

amino acids lysine and tryptophan, as well as niacin, an important member of the vitamin

B complex (Katz et al. 1974, 1975; among many others). Raw maize has relatively high

Sr/Ca compared to breast milk and meat products, but it is also notably low in total

mineral content, especially calcium.

Fortuitously, human societies across time and space have processed maize with

techniques that, while originally intended to facilitate digestibility, also improved its

nutritional value (see Katz et al. 1974, 1975; Bressani 1990; Bressani et al. 1990, 2002).

These treatments include the use of lime, wood/plant ash, lye and burnt shell ash to

produce alkaline solutions that soften and remove the external pericarp of maize (see

Katz et al. 1974), with lime and shell being the most common sources of alkali for the

ancient Maya.

In Mesoamerica, the process of alkali treatment, or nixtamalization, generally entails:

1) near boiling of dried maize in a 5% solution of lime in water for 30-50 minutes

(mixing maize with lime produces a dilute calcium hydroxide solution that is basic, or

alkaline, in pH); 2) discarding of the maize pericarp after cooling the mixture; 3)

thorough washing and draining of the remaining maize; and 4) fine grinding of the

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remaining maize into a dough called masa (Katz et al. 1974: 174; 1975). This dough can

be made into tortillas by cooking on a hot clay or metal griddle, or used to make

sourdough, tamales, maize gruel or a stew ingredient.

During the process of lime soaking and heating, maize notably loses some

constituents. These include essential amino acids (excluding lysine), thiamin, riboflavin,

niacin, nitrogen, iron, zinc, fat and crude fiber (Bressani 1990; Bressani et al. 1958, 1990,

2002). However, the overall outcome is an enhancement of nutritional (biochemical)

quality, particularly a significant increase in bioavailable calcium, doubling (or more) of

essential amino acids, improved protein quality, and the release of otherwise almost

unavailable niacin (see Katz et al. 1974; Bressani et al. 1958, 1990, 2002).

As malnutrition can result from high consumption of untreated maize, it has been

concluded that societies that relied on maize as a major dietary staple (half to two thirds

of total diet) likely practiced a form of alkali processing (Katz et al. 1974; 1975). This is

supported by ethnographic analogue and cultural continuity of such cooking practices in

Latin America today, but it is also inferred by archaeological evidence. This includes

lime-encrusted vessels at Teotihuacan, Mexico dating to 100 B.C. (C.C. Kolb, pers.

comm. to Katz et al. 1974: 183), Terminal Classic (or earlier) jars with lime deposits at

Lamanai, as well as lime-coated colanders from Postclassic Lamanai (White 1986: 85).

Observations by Landa (1566, in Tozzer 1941) also indicate that Maya in the Yucatan

treated maize with lime at the time of Spanish contact.

Significantly for this study, the act of alkali processing produces maize that is

enriched in calcium by orders of magnitude (Bressani et al. 2002; Burton and Wright

1995; Wright 1994). For instance, Wright (1994) found that tortillas treated with lime

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exhibit Ca values six to twenty times higher than unprocessed maize. Bressani and

colleagues (2002) found that this process increased Ca by as much as 24 times in the

maize germ. Such calcium enhancement can be viewed as an evolutionary adaptation

that played a key role in preventing calcium deficiency, which is significant for

populations whose diet can verge on such deficiency due to low consumption of animal

products such as milk (Bressani et al. 1958, 2002).

High Ca renders maize Sr (as well as Ba) ineffective (or “invisible”) in influencing

hard tissue Sr/Ca to resemble its relative concentration in untreated maize (Burton and

Wright 1995). This is because increased calcium intake will reduce the level of strontium

absorption and retention by the body. Hard tissue strontium is not directly correlated

with the particular Sr/Ca ratio of plant or meat foods, but rather the average dietary Sr/Ca

ratio, which can be affected by certain cooking practices. When examining Maya diet,

one must consider that hard tissue strontium will be “disproportionately sensitive” to high

calcium foods such as alkali-treated maize (Burton and Wright 1995). According to

Burton and Wright (1995: 278), a specific food such as maize must make up more than

90% of the total diet before the dietary and hard tissue Sr/Ca will reflect that food’s Sr/Ca

ratio.

Katzenberg (1984) and Szpunar (1977) previously recognized this in studies of

ancient bone chemistry and maize diets, but, according to Burton and Wright (1995), they

had incorrectly attributed the “paradoxical” effect to low Sr in maize, rather than its low

total Ca (mineral) content. Similarly, Price and Kavanagh (1982) found that despite

archaeological and isotopic evidence for increasing maize intake in American Late

Woodland groups (Bender et al. 1981), bone Sr values were low instead of high,

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contradicting the general association of elevated Sr values with high plant consumption

(see Chapter Four).

To illustrate the effect of food Ca on the Sr/Ca ratio, Burton and Wright (1995)

examined the combined effects of two and three component diets on the total Sr/Ca ratio.

In this case, meat, beans and corn represent some major items in a traditional Maya diet.

The authors found that in a diet composed of meat and beans, the high Ca and Sr levels of

beans, compared to meat, were over represented in the overall bone Sr/Ca ratio. As they

state, unless the diet was mostly composed of meat products, the total dietary Sr/Ca ratio

(and bone Sr/Ca) would almost entirely be derived from the beans (Burton and Wright

1995: 278).

In a diet composed of meat, beans and (alkali-treated) maize, even when meat levels

remain constant, increasing maize consumption results in a decreasing Sr/Ca ratio, as the

high Ca (low Sr/Ca) maize signature dominates the total ratio (Burton and Wright 1995).

Diets with the same plant/meat ratio can exhibit different Sr/Ca and Ba/Ca due to

variations in Sr, Ba and Ca in the plant foods ingested. Conversely, diverse diets can

result in similar Sr/Ca and Ba/Ca ratios in hard tissues, particularly if high calcium plants

provide the main source of dietary calcium (Burton and Wright 1995; Burton et al. 1999).

In total, for paleodietary reconstruction based on strontium, more research is needed to

assess the Sr/Ca relationships in various food items and their combined effect on hard

tissue composition.1

1 Cleary, for any paleodietary reconstruction based on hard tissue Sr/Ca data, the carbon and nitrogen isotopic composition of

comparable hard tissues should also be analyzed to determine if low Sr/Ca actually reflects high meat intake or high alkali- treated

maize intake. The repercussions of misinterpreting such scenarios for status- or gender-related differences in diet are considerable.

For Lamanai, White (1986) has examined 15N and 13C isotopic values in bone to reconstruct diet and the chemical distinctions

related to gender and socioeconomic status. Such evidence, in addition to strontium results, indicate that status distinctions among the

ancient Maya can be recognized in hard tissue composition reflecting relative maize and meat intake (also see Coyston et al. 1999; Gerry 1993; White 1999; White and Schwarcz 1989; White et al. 1993; Wright and White 1996) (see Section 4.4).

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On a practical level, it is unlikely that Maya infants consumed a maize diet that was

not processed according to the treatment of adult maize foods, simply for digestion

purposes. Maize gruel is produced by boiling ground maize dough in water, often with

the addition of flavorings such as honey and seasonings. The dough is derived from

ground maize that was likely processed with lime or other alkali ingredients (e.g., shells

[Nations 1979]). In this case, one expects the Sr/Ca ratio to be reduced compared to the

Sr/Ca ratio of raw maize. Based on Wright’s (1994) observations of calcium enrichment

in tortillas, one can expect the Sr/Ca ratio of lime-treated maize to be reduced six to

twenty times compared to raw maize. (However, the extent of calcium enrichment in

maize atole is unknown and may differ from tortilla values due to its watery base [see

Chapter Eight].)

Nevertheless, Lamanai mothers would have consumed the same calcium-rich maize

during lactation, producing a reduced Sr/Ca breast milk that would be further diminished

due to mammary gland discrimination. Infants consuming low Sr/Ca breast milk will

also have low hard tissue values, and despite lime processing, maize weanling foods

(watery gruel) will remain enriched in Sr/Ca compared to breast milk (see Chapters Five

and Eight). The transition from exclusive nursing to maize supplementation should

therefore be reflected in the increasing Sr/Ca composition of an individual’s hard tissues

developing at that age. This is the fundamental premise of this investigation and it

capitalizes on the reliability of hard tissue strontium to chronicle dietary intake and the

weaning process.

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CHAPTER 5

BREASTFEEDING, WEANING AND INFANT HEALTH

Breastfeeding is an intricate dance between mother and child,

during which the child’s physical, cognitive, and emotional well-being

are nurtured, and through which they flourish.

(Dettwyler 1995: 65)

5.1 The Nutritional Qualities of Human Breast Milk

As universally acknowledged, breast milk is the perfect food for young infants,

containing more than 200 recognized constituents with physiological significance. As a

food, it contains a vast array of bioactive compounds that are required for normal growth

and development, and which confer immunity to infants with immature immune systems.

These highly bioavailable constituents include enzymes, growth factors such as

epidermal growth factor (EGF), prostaglandins and prolactin, hormones, peptides,

glycoproteins, amino acids and glycoproteins responsible for intestinal maturation, and

immunological protection against microbial pathogens in the form of IgA antibodies,

leukocytes, lysozyme, lymphokines and lactoferrin (see Table 5.1).

Generally, lactation can be divided into three stages, based on milk composition: 1)

the immediate period (up to one week) after birth, when breast milk is referred to as

colostrum; 2) a period of “transitional milk” from one to three weeks after birth; and 3) a

period of “mature” breast milk from three weeks onward (Institute of Medicine 1991).

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Table 5.1 Constituents of human milk

(from Institute of Medicine 1991: 114)

Classes of Constituents in Human Milk

Protein and Nonprotein Nitrogen Compounds Carbohydrates

Proteins Lactose

Caseins Oligosaccharides

-Lactalbumin Bifidus factors

Lactoferrin Glycopeptides

Secretory IgA and other immunoglobulins

-Lactoglobulin Lipids

Lysozyme Triglycerides

Enzymes Fatty acids

Hormones Phospholipids

Growth factors Sterols and hydrocarbons

Nonprotein Nitrogen Compounds Fat-soluble vitamins

Urea A and carotene

Creatine D

Creatinine E

Uric acid K

Glucosamine

-Amino nitrogen Minerals

Nucleic acids Macronutrient Elements

Nucleotides Calcium

Polyamines Phosphorus

Magnesium

Water-Soluble Vitamins Potassium

Thiamin Sodium

Riboflavin Chlorine

Niacin Sulfur

Pantothenic acid Trace Elements

Biotin Iodine

Folate Iron

Vitamin B6 Copper

Vitamin B12 Zinc

Vitamin C Manganese

Inositol Selenium

Choline Chromium

Cobalt

Cells

Leukocytes

Epithelial cells

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However, the concentration of human milk constituents varies considerably both

within and among women, i.e., at different stages of feeding, diurnally, from day to day,

and at different stages of lactation. Maternal nutrition determines human milk

composition in three ways: 1) current dietary intake, 2) nutrient stores, and 3) alterations

in nutrient utilization influenced by hormonal characteristics of lactation (Institute of

Medicine 1991). Specifically, milk composition is affected by all the factors that

influence plasma composition, hormones, and non-nutritional influences such as nursing

frequency, environmental conditions (e.g., exposure to infections) and length of gestation.

Abundant evidence indicates that short-term decreases in dietary intake and/or

quality, even among undernourished women, will not significantly affect nutrient content

in breast milk (Dorea 1999, 2000; Institute of Medicine 1991; Laskey et al. 1998;

Lonnerdal 1986a,b; Prentice et al. 1994). In such cases, women are still able to produce

milk with adequate protein, fat, carbohydrates, folate and most minerals, including iron

and zinc (of which breast milk is a good source) (Dallman 1986; Institute of Medicine

1991; Lonnerdal 1986; Lonnerdal et al. 1981; Murray et al. 1978; Siimes et al. 1984). To

maintain nutrient levels in the face of malnutrition, nutrients for milk synthesis derive

from maternal stores or body tissues.

In general, major minerals such as Ca, P and Mg are tightly regulated in maternal

serum, so that maternal intake of such nutrients will not significantly alter breast milk

composition (Cross et al. 1995; Institute of Medicine 1991; Krebs et al. 1997; Laskey et

al. 1998; Prentice et al.1994). Other factors that do not appear to consistently and

significantly alter breast milk Ca (and P) concentration include maternal malnutrition

(unless there is severe calcium deficiency), maternal age, race, socioeconomic status,

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infant gestation length, metabolic disorders, stage of lactation, milk volume, child

weaning, smoking habit, calcium and vitamin D supplementation, prolonged medication

use (e.g., oral contraceptives) and sampling technique (DeSantiago-Soledad et al. 2002;

Dorea 1999; King et al. 1992; Laskey et al. 1998; Prentice and Barclay 1991).

Thus, while previous dietary guidelines for pregnant and lactating women

recommended significant increases in Ca intake, this is no longer the case in North

America (see Allen 1998). During pregnancy and lactation, Ca mobilization to the

developing child is maintained by increased efficiency of maternal metabolism, which is

not affected by maternal Ca consumption (Allen 1998; Cross et al. 1995; King et al.

1992; Krebs et al. 1997; Laskey et al. 1998; Sowers et al. 1993). Even with lactation-

induced bone loss, particularly the whole-body mineral content of trabecular bone in the

spine and femoral neck (e.g., Laskey et al. 1998), epidemiological data indicates that

there is a subsequent complete replacement of such mineral loss (Cummings et al. 1995;

Koetting and Wardlaw 1988).

Breast milk calcium content is still variable, however, as indicated by data surveyed

over the last fifty years from around the globe (see Dorea 1999, 2000). Mean calcium

concentrations have ranged from 84 to 462 mg/L (with a median of 252 mg/L) (Dorea

1999), though most data reflect a range of 200-300 ppm (Krachler et al. 1999), or a mean

Ca concentration of approximately 280 mg/L in mature human milk (Institute of

Medicine 1991: Table 6-1). Comparative data for Maya women consuming a traditional

diet is not known, as is the effect of local geology on Maya breast milk, but data for rural

Mexican Otomi women subsisting on a similar high-maize, low-fat/protein diet indicates

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mean breast milk Ca concentrations of 268 µg/g (ppm) at four months of lactation and

240 µg/g (ppm) at six months of lactation (Villalpondo et al. 1998: Table 3).

Within individuals, noticeable differences in the concentration of calcium over time,

that are unrelated to nutritional status, include significant increase in Ca content during

early lactation (1-3 months), followed by a decline after 6 months of nursing, to a level

lower than in earlier stages (Karra et al. 1988). Similarly, cross-culturally, in both healthy

and malnourished mothers, zinc steadily decreases over the course of lactation (Karra et

al. 1988).

To an extent, maternal nutrition during lactation has little impact on infant growth.

This has been shown by studies in Taiwan (Adair and Pollitt 1985), Columbia (Herrera et

al. 1980) and Guatemala (Lechtig and Klein 1980), among others. Whitehead and Paul

(1984) found that the growth of breastfed infants in the first four to six months of life did

not differ significantly between industrialized and developing countries.

However, chronic malnutrition and ill health in pregnant and lactating mothers will

result in some physiological consequences for developing offspring. The nutritional

status of exclusively breastfed infants is dependent on three major factors: 1) infant

nutrient stores, which are determined by placental nutrient transfer in utero, gestation

length and birth weight; 2) amount and bioavailability of nutrients provided by breast

milk; and 3) environmental and genetic factors that affect the infant’s rate of nutrient

utilization and nutritional status, such as growth, infections and disease (see Institute of

Medicine 1991).

Allen (1994) has found that lactating women are more likely to suffer from

micronutrient deficiencies that can ultimately affect breast milk composition and infant

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development. Other studies have also associated increased infant growth with maternal

supplementation and breast milk quality (Delgado et al. 1982; Herrera et al. 1980). In

particular, chronic malnutrition will affect vitamin levels in breast milk, particularly

vitamins A, B6, B12 and D (Institute of Medicine 1991). Some studies have also found

correlations between maternal Zn intake and Zn content in breast milk, especially in cases

of Zn supplementation (Karra et al. 1988).

5.2 Determining Factors in Breastfeeding and Weaning Behavior

Despite being the principal means of infant nutrition, breastfeeding is a highly

variable behavior that is subject to numerous biological and cultural demands. Current

Western beliefs promote prolonged breastfeeding, noting the nutritional, immunological

and emotional benefits. Conversely, analyses of the nutrient quality of breast milk and

the growth requirements of young children suggest that infants require additional

nutrients by six months of age. For instance, if breast milk is the only consumed food,

there is a risk of iron deficiency by the age of six to nine months (Institute of Medicine

1991). Some exclusively breast-fed rural Maya infants even begin to falter as early as

three months of age (Rivera and Ruel 1997). As a result, weaning is an event of great

importance to the well-being of children and is significant in nutritional research.

In discussing infant health and nutrition, weaning is more appropriately defined as the

complete cessation of breast milk intake, rather than the process of dietary

supplementation, which is also known as “supplementary” or “complementary” feeding.

Such definitions are important, as many weaning studies are not clear about whether they

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refer to the onset of weaning, the rate that new foods replace breast milk, or the complete

cessation of nursing (see Schurr 1997).

In this study, examination of Sr/Ca changes in permanent dental enamel represents

the introduction and rate of non-breast milk supplementation among infants. Rather than

being a single, abrupt event, weaning is the outcome of an extended, gradual, process that

involves two dietary transitions. Supplementation, or the gradual introduction and

increased consumption of non-milk weanling foods (beikost) after a period of exclusive

breastfeeding, represents the first transition, or the onset of weaning. This process is

accompanied by the concomitant decline of breast milk intake at a variable rate, which is

replaced with alternate sources of liquid. Over many months, supplementation is stepped

up, while breastfeeding is reduced, until the child is weaned completely off breast milk.

Hence, the ideal measure of weaning behavior accounts for both the timing (age of onset)

and rate of weaning, in addition to the chemical composition of childhood diet (Schurr

1997).

The consumption of supplementary foods has a complex effect on the total amount of

nutrient absorbed by infants, including 1) adding nutrients in a less bioavailable form; 2)

decreasing the bioavailability (impairing the absorption) of nutrients (e.g., iron) in human

milk; and 3) decreasing the intake of breast milk and other important factors in milk (see

Institute of Medicine 1991: 154).

Most importantly, the period and pattern of breastfeeding is both a biological and

culturally determined process. Cultural beliefs about weaning age can affect birth

spacing, maternal nutrition and the physiological and emotional health and growth of

young children. Understanding the cultural determinants of weaning is essential.

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In practical terms, weaning depends on factors such as mother and infant health; rate

of physiological, neurodevelopmental and behavioral maturation; interest in food;

number of erupted teeth; available food types that are considered suitable for child

digestion; relative cost of supplementary foods; mothers’ perceptions of a child’s

developmental progress or delay (i.e., wasting); and, importantly, cultural beliefs about

appropriate age (see Ballabriga and Rey 1987; Dettwyler and Fishman 1992; Fildes 1986;

Konner and Worthmann 1980; Lawrence 1989; Martorell and O’Gara 1985; Stuart-

Macadam and Dettwyler 1995, among others).

Nursing practices are influenced significantly by living standards (socioeconomic

status), individual needs, tradition and religious beliefs, customs, structure of the

mother’s daily activities, and beliefs about where the child sleeps at night. Other

culturally-specific beliefs include issues of contamination of supplementary foods; the

nature of infancy; notions of “proper” relationships between mother and child, between

mother and father, and their perception by society; and ideas about personal

independence and autonomy.

Sex of the child can also play a role in determining weaning behavior. For instance,

mothers have been reported to nurse male infants longer than their female infants in

Canada, Sweden, Ireland, France, Guatemala, Ecuador, Brazil, Peru, Taiwan, India,

Jordan, Liberia and Botswana (see Fildes 1986; McKee 1984). In extreme situations, the

disparate weaning patterns play a direct role in disease incidence, infant growth and

development, and ultimately, child survival, i.e., death of malnourished female infants

(see Stuart-Macadam 1995a: Figure 1.1).

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Indeed, weaning represents a nutritional and health transition in early childhood with

adaptive significance for later life. Other than fulfilling its immediate role of nourishing

a developing child, breast milk and its astounding array of bioactive ingredients bestow

numerous advantages. These are principally related to breast milk’s role in infant

immunological development, intestinal growth and maturation (Bines and Walker 1991)

and neurodevelopment.

Specific benefits of breastfeeding for human offspring include: reduced rate of food

and environmental allergies (Kramer 1988); lower risk of jaundice, ear, gastrointestinal

and respiratory infections (Cunningham 1995; Duffy et al. 1986; Mata et al. 1967; Glass

et al. 1983), cancer (Davis et al. 1988; Freudenheim et al. 1994; Micozzi 1995), Crohn’s

disease and colitis (Cunningham 1981, 1995; Institute of Medicine 1991; Stuart-

Macadam 1993); prevention of iron deficiency (Calvo and Gnazzo 1990; Oski and

Landaw 1980); and increased body activity and stronger arousal reaction, which are

related to enhanced cognitive and neurodevelopment (Bauer et al. 1991; Fergusson et al.

1982; Lucas et al. 1992; Rogan and Gladen 1993; Temboury et al. 1994). Altogether,

such advantages result in greater adulthood survival of breastfed infants who are not

genetically prone to disease.

A survey of developed countries between the period of 1850-1950 found distinctly

lower mortality rates among breastfeed infants, compared to bottle-fed infants (see

Institute of Medicine 1991: Figure 7-1). In developing countries, exclusive breastfeeding

is also associated with the lowest mortality and infectious disease rates among young

infants (Institute of Medicine 1991). In early life (i.e., first year), shortened breastfeeding

is clearly associated with high infant mortality (Knodel and Kintner 1977).

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On the other hand, after the first year, the association between breastfeeding and

mortality is inconsistent, with some studies finding no protection against excess mortality

during the second and third years of life, while others indicate continued protection until

the third birthday (Briend et al. 1988; Institute of Medicine 1991).

Importantly, with respect to morbidity and mortality risk, besides providing

antimicrobial, anti-inflammatory and immunologic stimulating agents (Goldman and

Goldblum 1990; Goldman et al. 1990), breastfeeding protects young children against

infectious diseases by limiting exposure to potential pathogens in contaminated foods.

Other cultural factors associated with breastfeeding that reduce morbidity include the

lesser likelihood of breastfeeding mothers to engage in health-risky behavior such as

smoking, which reduces the risk for respiratory infections, and the reduced exposure to

infectious disease that accompanies increased contact with non-maternal caregivers when

an infant is not dependent on breast milk (and mom) for food. As a result of reduced risk

of infection and malnutrition among breastfed infants, in areas of poor sanitation in

developing countries (low income), such infants tend to grow more rapidly than formula-

fed infants in the first six months of life (see Institute of Medicine 1991).

In mothers, prolonged breastfeeding has the immediate effect of increasing the

duration of lactational amenorrhea, which results in increased birth spacing (Anderson

1983; Habicht et al. 1985; Hobcraft 1987; Lee 1980; Short 1983; Thapa et al. 1988).

This reduced fertility benefits both survival of the mother in subsequent pregnancies, as

well as survival of infants (Ellison 1995; Hobcraft 1987; Thapa et al. 1988, among

others). The effects of child spacing are dependent on socioeconomic status, however,

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with only limited impact on survival in developed countries (Fedrick and Adelstein

1973), and further research is needed for disadvantaged groups.

In addition, breastfeeding appears to benefit the mother by reducing the risk of

reproductive cancers (Byers et al. 1985; Ing et al. 1977; Micozzi 1995; Newcomb et al.

1994; Post 1982; Schneider 1987, among others); and possibly increasing bone mineral

density and lowering the risk of fractures and osteoporosis (Aloia et al. 1983; Cumming

and Klineberg 1993; Feldblum et al. 1992; Hreshchyshyn et al. 1988, among others).

(Note, however, that the evidence for bone density and fracture incidence is not entirely

consistent [e.g., Chan et al. 1982; Hayslip et al. 1989; Institute of Medicine 1991].)

At the same time, while primarily protecting infants, breastfeeding can also be the

mechanism through which infants contract infectious diseases. Depending on hygiene

and pathogen load in the living environment, enteropathogens such as Shigella and

Salmonella can contaminate human milk through the areola and nipples of the breast,

consequently infecting nursing infants (Mata et al. 1967; Wyatt and Mata 1969).

Mothers infected with viruses such as cytomegalovirus, hepatitis B, rubella, human T

lymphocytotropic virus type 1 (HTLV-1) and possibly, human immunodeficiency virus

type I (HIV-1), can also produce breast milk containing such pathogens (Institute of

Medicine 1991).

Besides breast milk transmission of disease, extended nursing can also lead to

increased susceptibility of infants to infectious disease. In this way, exclusive

breastfeeding (or minimal food supplementation) after six months of age, when infants

require additional nutrients for growth and development, can result in malnutrition that

renders children vulnerable to infection.

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At the same time, infectious disease and malnutrition can prompt mothers to

withdraw solid foods and resume intensive nursing because they often associate illness,

particularly gastrointestinal disorders, with solid food intake (see Dettwyler and Fishman

1992; Fildes 1986; Stuart-Macadam and Dettwyler 1995; Wood 1983). In fact,

undernourished and underdeveloped children are sometimes nursed longer than healthy

infants because mothers associate increased mortality risk with the period after weaning

(Caulfield et al. 1996; Simondon and Simondon 1998). A vicious cycle of chronic

malnutrition and infectious disease can result, often with fatal effects.

Like the synergistic cycle of infectious disease and malnutrition, the ability to

breastfeed adequately is negatively affected by illness (due to physical weakness and/or

separation from mothers), and directly leads to delayed infant development. Furthermore,

with prolonged avoidance of breastfeeding, breast milk production is reduced and it is

often difficult to resume nursing after recovery. Thus, it is often illness that results in

nursing interruption, rather than lack of breastfeeding that leads to infant ill health.

5.3 The Biological Bases for Breastfeeding Duration and Weaning Age

As there are various physiological consequences to changes in weaning patterns,

particularly repercussions that affect survival, the overriding question is “at what age

were most children weaned in the past?”

In a noteworthy study, Dettwyler (1995) carefully examined the primate and cross-

cultural human data to construct a “hominid blueprint” for breastfeeding and weaning

that ensures optimal physical, cognitive and emotional health for infants. Ultimately,

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these inferences can shed light on the underlying biological basis for human weaning

patterns, irrespective of cultural beliefs. As she states, this question encompasses infant

nursing frequency, timing of solid food introduction, and the age at which breast milk

intake is completely ceased.

Biologically, there are several theories as to when human mothers normally wean

their children. In general, they are based in relation to developmental factors, namely: 1)

tripling or quadrupling of birth weight; 2) attainment of one-third adult weight; 3) 2.71 x

adult female body weight (Harvey and Clutton-Brock 1985); 4) length of gestation; and

5) age at eruption of first permanent molar (see Dettwyler 1995). In terms of

development, weaning is specifically dependent on factors such as mechanical ability

(chewing, swallowing), functional capacity of the gastrointestinal system (esophagus,

stomach, small and large intestines, pancreas) and child appetite.

From the primate data, it appears that compared to primates with small neonates,

those with large neonates tend to have relatively long gestation periods, late weaning age,

late sexual maturity age, large neonatal and adult brain sizes, and a long life span (Harvey

and Clutton-Brock 1985). As large primates with relatively large neonates, humans

would then be expected to have one of the latest weaning ages (Dettwyler 1995). For

instance, among great apes, orangutans breastfeed for 4.21 x gestation length in months;

gorillas, 6.18 x gestation; and chimpanzees, 6.4 x gestation length (Dettwyler 1995: Table

2.3). Drawing from this, Dettwyler (1995: Table 2.3) estimates a minimum weaning age

of 6 x Gestation Length for humans, or 54 months (4.5 years).

Harvey and Clutton-Brock (1985) have compiled various human data to arrive at a

regression formula for calculation of weaning age. Namely, weaning age in days equals

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2.71 times the adult female body weight in grams. From this equation, a weaning age

range of approximately 2.8 to 3.7 years is suggested, accounting for variation in adult

female body weight. However, Dettwyler (1995: 52) advises that this range represents

the minimum ages at weaning since Harvey and Clutton-Brock used a relatively young

weaning age of 720 days for humans in developing their overall regression for primate

subfamilies (which results in underestimations of weaning age for all primates, including

humans). As it turns out, a late weaning age of around five to six years also coincides

with developmental achievements such as eruption of the first permanent molar (Smith

1989, 1991a,b, 1992), which facilitates food processing, and full adult immune

competence.

With respect to immunology, it is clear that components of breast milk are crucial.

While lactoferrin, an iron-binding protein, prevents the growth of iron-requiring toxigenic

bacteria such as Bacteroides, Clostridium, Escherichia, Salmonella and Staphylococcus

(Weinberg 1994), lymphokines prime the active immune response of children until they

achieve adult immune competence (IgA, IgG, IgM) (Hahn-Zoric et al. 1990; Pabst and

Spady 1990; D. Fredrickson, pers. comm. to Dettwyler 1995). Prolonged breastfeeding

then ensures that children are immunologically capable once weaning occurs. Beyond a

developmental coincidence, Dettwyler (1995: 56) believes that “the fact that children’s

immune systems do not become mature until six years of age is understandable if we

assume that the active immunities provided by breast milk were normally available to the

child until about this age”.

In total, accounting for one-third adult weight, first permanent molar eruption,

gestation length, adult female body weight and birth weight quadrupling, the range of

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human weaning times is between two and a half and six years of age (see Dettwyler

1995: Figure 2.3). This is supported by a plethora of human studies. A wide variety of

ethnographic data point to weaning ages significantly longer than the current Western

standard, which, for the first time in human history, has replaced maternal breast milk

with artificial substitutes. For example, ancient Babylonians and Egyptians commonly

breastfed up to three years of age (Fildes 1986: Table 15.2); Wickes (1953) reported an

average weaning age of three to four years among various contemporary tribes; Konner

and Worthmann (1980) observed intensive breastfeeding for three to four years among

!Kung hunter-gatherers; a survey of forty-six non-industrialized societies found almost

75% weaned between two and three years of age, 25% at eighteen months and 1% at six

months (see Lawrence 1989); and in the pre-industrial West, children were routinely

breastfed until two to four years of age (see Dettwyler 1995; Fildes 1986, 1995; Stuart-

Macadam 1995). Three to four years is also the same period reported for self-weaning

among children who nurse for as long as they want (Dettwyler 1995).

For the Maya, early colonial and contemporary ethnographic evidence indicate that

pre-contact and later pre-industrial children were extensively breastfed, then weaned onto

atole, a watery maize gruel made by boiling ground (alkali-processed) maize with water

(Behar 1968; Benedict and Steggerda 1937; Landa, in Tozzer 1941). White (1986) notes

that there is no evidence that beans and/or meat supplements were given to children

during the weaning process. However, in addition to atole, which is commonly drunk by

Maya of all ages at breakfast, present-day Guatemalan Ladinos also wean children on

small quantities of softened corn tortillas and black bean broth after six months of age

(Izurieta and Larson-Brown 1995).

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In general, it is believed that the food habits of rural Maya, principally their reliance

on maize (and atole for weaning infants), have remained more or less stable since ancient

times. Modern surveys indicate that the rural Mexican diet provides 70% of total energy

as carbohydrates (predominantly maize), 11% as protein (beans and some meat), and

19% as fat (see Villalpando et al. 1998). This accords well with Lamanai bone isotopic

evidence of maize consumption reaching 70% of total diet in the Postclassic (White 1986).

This continuity also applies to the extended period of breastfeeding that is

documented in both contemporary and contact period times. In particular, ethnohistorical

evidence from Friar Diego de Landa sheds some light on the childcare practices of 16th

century Maya in the Yucatan (see Tozzer 1941). Yucatec Maya at this time were

described as healthy and robust people who had an adequate and diverse diet. As such,

fecundity was high and mothers traditionally nursed their children for three to four

years (Landa, in Tozzer 1941). In contemporary times, the mean duration of

breastfeeding in indigenous Guatemalan (Maya) communities is two years (Wright and

Schwarcz 1998), while Guatemalan Ladinos breastfeed for an average of 15 months

(Izurieta and Larson-Brown 1995).

While breast milk is considered a nutritionally superior food for infants, compared to

low quality weanling foods, its nutritional value is unquestionably dependent on the

length of lactation. After six to nine postnatal months, breast milk quality significantly

declines. Anemia is a viable health risk when breast milk remains the primary (or

exclusive) food source after an extended period. Iron deficiency is a significant

nutritional problem globally, and even in contemporary times, it is estimated that the

worldwide prevalence of anemia in children between birth and four years of age is 43%,

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with significant differences between economically developed and underdeveloped

countries (Institute of Medicine 1991: 159). Among Lamanai Maya, hard tissue evidence

suggests that well over one third of the population was anemic at some point in their lives

from the Postclassic period onward (White 1988: 15).

For the Maya, extended breastfeeding and supplementation with iron-poor maize

(which contain iron-binding phytates) may have been a significant factor in poor infant

health. Combined with parasitic and infectious diseases and ensuing diarrhea, an iron

and protein deficient diet fed a synergistic cycle that increasingly compromised infant

health and nutrition. For the Lamanai Maya, the interaction of such factors was

instrumental in making weaning age a critical period of childhood (White 1986; White et

al. 1994).

As stated in Chapter Two, White and colleagues (1994) believe that hard tissue

evidence of chronic infectious diseases, particularly during the Historical period, reflect a

common weaning age, between two and six years, and the period of highest risk for

infectious and parasitic diseases among Lamanai children. Lamanai bone chemical

evidence supports ethnohistorical data that children were weaned onto maize, and further

indicates that children consumed high levels of maize comparable to adults throughout

the Postclassic and Historical periods (White 1986).

All told, overwhelming ancient and contemporary evidence points to a range between

two and five years of age for children to be weaned (Stuart-Macadam and Dettwyler

1995; Fildes 1986; Lawrence 1989, among others). While this wide range is partially the

result of culturally-prescribed customs, it is also reflective of the various human

adaptations to different geographic zones, climates, dietary resources and pathogen loads.

125

5.4 Methods of Identifying Weaning Patterns in the Past

Owing to the importance of early childhood health in the overall health status and

survival of a population, numerous approaches have been adopted to recognize weaning

patterns in ancient populations. Traditional methods have examined infant mortality rate

and paleodemography (Clarke 1980; Cook 1976; Herring et al. 1998; Katzenberg et al.

1996; Knodel and Kintner 1977; Lallo 1973; Saunders and Herring 1995; Swedlund

1990); deciduous tooth wear (Farnum and Benfer 1995; Molleson 1995); and non-

specific hard tissue indicators of physiological stress, e.g., enamel hypoplasia (Corruccini

et al. 1985; Hillson 1979; Blakey et al. 1994; Farnum and Benfer 1995; Goodman et al.

1984; Goodman and Armelagos 1988, 1989; Lanphear 1990; Moggi-Cecchi et al. 1994;

Song 1997; Wood 1996; Wright 1990). However, the suitability of such studies has been

complicated by 1) methodological issues; 2) variations in hard tissue development; 3)

conflicting results, i.e., contradicting documented weaning age; and 4) the biased nature

of ancient burial samples (i.e., population misrepresentation, particularly of subadults [a

sample that has died prematurely], and true skeletal “health” [see Wood 1992]).

To better assess the effects of dietary behavior on hard tissues, chemical methods of

hard tissue analysis have been applied to trace breast milk intake and weaning. Such

studies have focused on isotopes of nitrogen (Dupras et al. 2001; Fogel et al. 1989;

Herring et al. 1998; Katzenberg and Pfeiffer 1995; Katzenberg et al. 1993, 1996;

Richards et al. 2002; Schurr 1997, 1998; Tuross and Fogel 1994; White and Schwarcz

1994), carbon and oxygen (Dupras et al. 2001; Richards et al. 2002; Wright and

126

Schwarcz 1998); relative levels of zinc (Farnum and Benfer 1995; Grupe 1986); and

strontium/calcium ratios (Huhne-Osterloh and Grupe 1989; Sillen and Smith 1984).

Stable nitrogen isotopes have been used to infer changes in infant dietary behavior

because proteins in breast milk and solid foods differ in their nitrogen isotopic

composition. Importantly, the nitrogen stable isotope values of an organism’s tissues

(15

N) have been demonstrated to reflect the nitrogen isotope values of its diet (DeNiro

and Epstein 1981). Like strontium, there is a trophic level effect for nitrogen isotope

ratios in animals within an ecosystem, so that a carnivore’s tissues will have protein

nitrogen values approximately 3‰ higher than its prey (Schoeninger and DeNiro 1984).

In the food web, breastfed infants exist one trophic level above their lactating mothers

because they are consuming their mother’s tissues in the form of breast milk, which is a

good source of nitrogen. (At birth, infants will have 15

N values comparable to their

mothers.) With nursing, protein in infant tissues should be enriched by 2-4‰ in the

stable isotope of nitrogen (15

N), compared to their mothers. With the cessation of breast

milk intake, weaning is identified by a decline in 15

N of bone collagen back to adult

levels (Fogel et al. 1989; Katzenberg et al. 1993, 1996; Katzenberg and Pfeiffer 1995;

White and Schwarcz 1994).

This hypothesis has been tested by Fogel, Tuross and Owsley (1989) using fingernails

of contemporary infants and their mothers, in addition to bones of ancient infants.

Fingernail evidence indicate that breast milk intake is indeed reflected as nitrogen

enrichment, and that this enrichment is still apparent several months after the onset of

food supplementation. Nitrogen enrichment (trophic level shift) averaged 2.4‰ more

than mothers’ values, and was evident throughout the period of exclusive breastfeeding.

127

With supplementation (infant formula, dairy products, cereals), however, there began a

decrease in infant 15

N values toward those of mothers (Fogel et al. 1989).

Furthermore, bone collagen from prehistoric/protohistoric Tennessee Valley infants

(one year olds) also display 15

N enrichment (Fogel et al. 1989). Later, between eighteen

and twenty months of age, 15

N values decline significantly, which the authors interpret

to be evidence of non-breast milk consumption (cessation of breast milk as the main

source of protein).

Nitrogen enrichment associated with breast milk intake has also been observed in the

bones of historic period children from the Sully Site, South Dakota (A.D. 1650 to 1733)

(Tuross and Fogel 1994). In children between three months and two years of age, 15

N

was on average 1.6‰ enriched relative to adult bone remains. The highest bone collagen

15

N values (12.8‰) characterize the three-month to two year old group, while children

thereafter, aged two to five years, have a decreased 15

N value of 10.2‰ (Tuross and

Fogel 1994). From their sample, the authors conclude that for at least the first year,

infants were exclusively breastfed without significant supplementation of other nitrogen

sources. Weaning is thought to have occurred between the ages of two and six years.

Katzenberg and colleagues (1993) similarly found enriched 15

N values in infants

when compared to their mothers in Ontario Iroquoian samples dated to A.D. 1530-1580.

In particular, infants younger than two years had 15

N values 2-3‰ higher than adults.

This parallels ethnohistorical accounts of Huron groups nursing infants until two to three

years of age (Katzenberg et al. 1993). (In contrast, 19th

century Canadian infants of

128

European descent were shown by 15

N values to cease breastfeeding at around one year

of age, which was supported by historical data [Katzenberg and Pfeiffer 1995]).

Like indigenous groups throughout the Americas, children were weaned on the staple

maize, which is reflected in high 13

C values among older infants and young children

(Katzenberg et al. 1993). Similarly, infants whose mothers could not breastfeed, or those

whose mothers died in childbirth, were likely mostly consuming maize, which would be

indicated by relatively high 13

C values and 15

N values similar to those of adults

(Katzenberg et al. 1993).

Combining data from bone, skin, muscle and hair of prehistoric Nubians, White and

Schwarcz (1994) also found age-related differences in 15

N values that are attributed to

an extended period of breast milk intake. With a significant negative correlation between

15

N and age, they found a 3‰ enrichment in children aged from birth to six years

compared to adults. With respect to weaning, their observations of a gradual decrease in

15

N over the first six years of childhood point to a slow, extended, process, rather than a

sudden shift from total breast milk reliance to complete non-milk food intake.

In the case of Middle Mississippian maize horticulturalists from the Ohio River

Valley, an increase in 15

N values commenced after birth until it reached the highest

value between one and three years of age (Schurr 1997). The author attributes the

nitrogen enrichment to substantial breast milk intake during at least the first two years of

life, while the subsequent decline in nitrogen values indicate increasing consumption of

non-breast milk proteins from a weanling diet. Furthermore, based on Schurr’s non-

linear model, which is more accurate in tracing changes (nitrogen decline) related to

supplementation and weaning, the weaning process was a gradual one that began before

129

the age of two years. For at least six months after the start of supplementation, breast

milk continued to provide the bulk of dietary protein (Schurr 1997).

As indicated by these nitrogen studies, bone chemical composition yields a rather

broad time frame for changes in dietary intake. Beyond identifying the start of

supplementation as before two years of age (Fogel et al. 1989; Katzenberg et al. 1993;

Schurr 1997; Tuross and Fogel 1994) and continued breast milk intake until five or six

years of age (Tuross and Fogel 1994; White and Schwarcz 1994), finer details of the

weaning process are imperceptible. It is maintained that such general indications are

inadequate, especially since ethnographic data can already account for such a wide range

(see above).

Additionally, in order to adequately sample the breadth of childhood that experiences

breast milk intake and weaning, i.e., to trace the subtle changes of the weaning process,

skeletons of more infant categories are required. Unfortunately, three obstacles challenge

this requirement: 1) the nature of post-depositional environments to deteriorate

undermineralized subadult skeletons; 2) the differential interment of children in the

archaeological record; and 3) the degree of error in traditional methods of ageing skeletal

remains.

Wright and Schwarcz (1998) have also experimented with stable isotopic signals of

carbon and oxygen in enamel to trace weaning. Their research represents the first

attempt to infer childhood dietary behavior from the chemistry of dental hard tissues.

130

Subsequent analyses by Richards and colleagues (2002) on the nitrogen and carbon

isotopic composition of tooth dentine reflect the current research shift to dental tissues.1

In Wright and Schwarcz’s (1998) investigation, the recognition of weaning is based

on the fact that the ratio of 18

O and 16

O in body tissues reflects the source of water

imbibed as a liquid, and to a lesser degree, the oxygen obtained from food. As human

breast milk is derived from the body water pool, it is more enriched in 18

O than the

water ingested by a lactating mother (but reflective of maternal diet). Oxygen isotope

values will reflect differences in water intake attributed to breast milk versus non-breast

milk liquid. Thus, hard tissues of breastfed infants will be heavier in 18

O than those of

bottle-fed infants (Wright and Schwarcz 1998). For breastfed infants, declining breast

milk intake and supplementation with different water sources will be exhibited as lower

18

O values in later developing enamel.

Conversely, relative values of 13

C in enamel reflect processes of dietary

supplementation, particularly maize, which is enriched in 13

C. The consumption of maize

gruels prior to complete weaning would be identified as an increase in 13

C in enamel

forming at the time of supplementation.

According to Wright and Schwarcz (1998), 13

C and 18

O values of enamel material

point to a long, gradual, transition from breast milk to solid foods for most children at

Kaminaljuyu. Enriched 13

C values of premolars (which develop between two and six

1 Their comparison of dentine and bone isotopic composition indicates that tooth dentine in children up to 11 years of age is

enriched in δ15N compared to adult rib values, with a significant portion of dentine formed during breastfeeding, with little, or no

turnover since (Richards et al. 2002). Juvenile rib collagen δ15N decreases to adult levels after the age of two years, suggesting that

weaning occurred at this age. After weaning, for several years, juvenile rib 15N is decreased compared to adult rib values, indicating that children’s diet was lower in animal protein than the diet of adults. Importantly, they maintain that the delay between the cessation

of breastfeeding and its chemical expression in bone collagen is still not fully understood (Richards et al. 2002: 206).

131

years of age) suggest that children two to six years of age were eating more maize foods

than they had eaten as infants, which the authors expect if maize gruel formed the

weanling diet (Wright and Schwarcz 1998). Based on their results, they propose that

Kaminaljuyu children began solid food supplementation by at least one year of age, with

substantial amounts of solid food ingested by two years. Nevertheless, breast milk intake

probably continued until five or six years of age, as indicated by 18

O values in premolars,

pointing to a relatively late weaning age (Wright and Schwarcz 1998).

Recognizing the investigative nature of such research, the authors also present several

factors unrelated to weaning that might cause changes in chemical composition (18

O).

These include higher metabolic rates of young children, changing activity patterns with

age, or more rapid water usage related to smaller body size. In this case, body size and

metabolic rate are known to affect the magnitude of isotopic fluxes and fractionation

(Wright and Schwarcz 1998: 15).

Unfortunately, due to the total sampling (dissolution) of enamel from teeth of

different developmental age (first molar, premolar, third molar), which Wright and

Schwarcz utilize to infer chemistry changes through time, a precise assessment of

weaning age is not possible. Their dental analysis controls for issues plaguing bone

chemical studies, i.e., bone turnover and hard tissue contamination, but this method does

not compare to the subtle time-depth sampling capabilities of LA-ICP-MS (see Chapter

Six).

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5.5 Hard Tissue Strontium and the Inferences for Infant Nutrition

The present study addresses many challenges in paleonutritional chemistry by

analyzing time-sensitive dental hard tissues utilizing localized laser (micro)sampling

of enamel across known periods of development. Both features make this analysis

unique in reconstructing diet and weaning behavior of ancient children at specific ages of

development.

Particular attention is on strontium, in the form of strontium-calcium (Sr/Ca) ratios,

because this element is a reliable hard tissue indicator of dietary Sr/Ca (see Chapter

Four). Historically, such research has predominantly centered on the usefulness of

strontium to indicate degrees of herbivory or carnivory among human groups, but its

ability to also trace infant breast milk intake, relative to food supplementation, and

weaning is postulated in this study. The present study builds on the work of Sillen and

Smith (1984), who examined the Sr/Ca ratios of juvenile skeletons to determine the

timing of dietary supplementation until the age of weaning.

Strontium is used to infer the process of weaning because the Sr/Ca ratio of solid

foods is relatively high compared to the Sr/Ca ratio of calcium-rich human milk, where it

is practically non-existent (Schroeder et al. 1972; Sillen and Smith 1984). Comparatively,

breast milk exhibits Sr/Ca values ranging from 0.14-0.35 x 10-3

(Harrison et al. 1965;

Krachler et al. 1999; Rehnberg et al. 1969; Rosenthal 1981), while food such as maize

has significantly higher ratios of 1.129 x 10-3

(Wright 1994), 2 x 10-3

(LaVigne 2002) and

even 7.14 x 10-3

(Shacklette 1980; Watt and Merrill 1963), for example, which is

dependent on geological conditions.

133

In truth, strontium content varies minimally in dental tissues. Still, some variation in

strontium levels reflects dietary and age-related changes in humans. These are due to

variations in gastrointestinal discrimination, food and water sources, and most

importantly, for this study, its absence in human milk.

During fetal development, strontium is discriminated by the placental barrier. In

newborns, this fact combines with discrimination at the mother’s mammary gland to

produce the lowest Sr/Ca ratio in humans (Comar et al. 1957). This lower Sr/Ca ratio in

young mammals may be due to the high calcium demands during rapid growth in infants

(Sillen and Kavanagh 1982).

Among infants, Sr is increasingly discriminated against in favor of Ca due to

maturation of the kidneys and digestive system after the first year of life (Sillen and

Kavanagh 1982). This is reflected in high OR values (ratio of Sr/Ca in infant bones to

Sr/Ca in diet) among young infants that steadily decrease with age: 1.0 among neonates;

0.6 at one year; 0.25 at 3 years; 0.23 at 5 years; 0.18 at 10 years of age and adulthood

(Sillen and Smith 1984: Table 1).

During the process of dietary supplementation, infants consume solid foods and non-

breast milk liquids that have Sr/Ca ratios significantly higher than breast milk. Thus, low

Sr/Ca ratios in infant remains could be interpreted as evidence of exclusive breast milk

intake and lack of dietary supplementation. Increasing Sr/Ca ratios will reflect the entire

process of the introduction of dietary supplementation until weaning. (This differs from

nitrogen stable isotope ratios of hard tissue collagen, which reflect the cessation of

breastfeeding.)

134

Maximum bone Sr has also been found by Grupe (1986) to be associated with

minimum Zn levels among young children of weaning age, suggesting that Zn might be

an indicator of weaning stress. While Farnum and Benfer (1995) could find no statistical

change in Sr due to bone contamination, they found decreasing Zn levels over time in

young children, particularly in mid to late childhood. However, they could not determine

if low Zn levels were due to weaning stress due to prolonged breastfeeding and

inadequate protein supplementation, or stress due to other factors.

In their important study, Sillen and Smith (1983, 1984) found that Sr/Ca values of

medieval Arab bones gradually increase after birth, with individuals aged 1.5 to 3.5 years

having the highest values for the entire population (see Table 5.2). The authors note that

this is consistent with ethnographic data of traditional Palestinian Arabs who continue to

breastfeed until two to three years of age. Thereafter, Sr/Ca values decline to levels that

persist throughout adulthood (Sillen and Smith 1984). Assuming a consistent adult diet,

these lower values reflect the discrimination against strontium that occurs with age in the

mature (adult) gastrointestinal tract.

Table 5.2 Bone Sr/Ca changes from the Dor sample, Israel

(estimated Sillen and Smith 1984 data, in Katzenberg et al. 1996)

Age (years) N

Sr/Ca

(x 10-3

)

Range

Birth

2

1.50

1.4-1.6

0.5 3 1.75 1.5-2.0

1 10 2.25 1.5-3.0

2 2 2.50 1.7-2.9

3 5 2.25 1.8-2.8

8 11 1.60 1.3-2.3

Adult 1.80

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Huhne-Osterloh and Grupe (1989) similarly examined strontium concentration in

ancient (German) bones to estimate weaning age. They found the highest Sr/Ca ratios in

children aged six months to two years, the period for which they postulate dietary

supplementation and eventual weaning. Like Sillen and Smith (1984), bone strontium

levels decline in subsequent age groups (see Table 5.3).

Table 5.3 Bone Sr/Ca changes from the Schleswig sample, Germany

(data from Grupe 1986; Huhne-Osterloh and Grupe 1989;

derived from Katzenberg et al. 1996: Table 2)

Age

(in years)

N

(individuals)

Sr/Ca

(x 10-3

)

S.D.

(total sample)

Birth-0.5

6

0.58

2 5 0.72

4 3 0.63

14 6 0.51

Adult 78 0.53

0.16

Most recently, Mays (2003) investigated bone Sr/Ca to determine the duration of

breastfeeding in an English Medieval sample. Likewise, bone Sr/Ca indicated significant

age-related changes that could be associated with breastfeeding, supplementation and

weaning. In particular, significant Sr/Ca increase between one and two years of age is

interpreted as representing the period of significant food supplementation (Mays 2003).

Reflecting immature digestive systems, infants and young children (under two years)

exhibit higher Sr/Ca ratios than older individuals and adults (Mays 2003: 734). In this

sample, a steady decline in Sr/Ca from about two to eight years of age, when values then

resemble adults, indicates that most children in this sample were fully weaned by two.

136

Preliminary analyses of archaeological teeth in the Hampshire College Natural

Science lab suggest that weaning can also be recognized in strontium levels quantified by

LA-ICP-MS analysis of enamel. Ablation results of several ancient Anasazi canines

indicate increased Sr/Ca ratios in the mid-crown regions (Perez 1998). This increase,

occurring around three to four years of age, may indicate a trophic level shift associated

with dietary changes during a relatively late weaning period, when solid food,

presumably maize, consumption increased relative to breast milk. This finding is also

observed by Wright and Schwarcz (1998) in stable carbon and oxygen isotope analyses

of dental enamel for other Maya samples.

The combined evidence suggests that hard tissue strontium analysis is useful for

tracking breastfeeding, food supplementation and weaning. But while Sillen and Smith

(1984) first postulated this model almost twenty years ago, it has generally been

overlooked in paleonutritional research, which has largely concentrated on isotopic

analysis. Mays’ (2003) recent findings are the most notable since Huhne-Osterloh and

Grupe (1989). Moreover, diet-related changes in hard tissue strontium have never been

examined in human dental remains. This fact makes this research exciting and

worthwhile to the field of paleonutrition.

5.6 Enamel Sr/Ca and Infant Nutrition at Lamanai

As indicated by ethnohistorical sources, hard tissue pathology and enamel isotopic

data, it is likely that ancient Maya mothers breastfed their infants for periods of up to four

or five years. While supplementation with non-breast milk foods (maize) likely began

137

after six months of age, due to diminished nutritional quality of breast milk, prolonged

nursing is within the norms of many past and present human populations.

Chemically, this pattern of infant feeding can be characterized by 1) initial low Sr/Ca

values reflecting exclusive breastfeeding, followed by 2) a significant increase signaling

the start of supplementation, that then assumes 3) a gradual increase over the extended

time period that represents prolonged breast milk consumption, concluded by 4)

stabilization and slight reduction of Sr/Ca values to levels comparable to adults. Figure

5.1 illustrates such a model of Sr/Ca change during early childhood, which incorporates

information on human strontium absorption (Comar 1963; Rivera and Harley 1965;

Sillen and Kavanagh 1982), general patterns of infant food supplementation and weaning

(see above), and the original premise of Sillen and Smith’s (1984) research.

Figure 5.1 Proposed model of Sr/Ca behavior during infancy and early childhood

0 1 2 3 4 5

Age in years

Sr/

Ca R

ati

o

138

Bone chemical evidence suggests that Historical Maya at Lamanai consumed the

same variety and proportion of foods as their Postclassic ancestors, with children

continuing to consume comparably high levels of maize (two-thirds of total diet) as their

parents (White 1986). In this case, nutritional stability might also extend to infant

feeding and weaning patterns.

However, while details of the Maya menu were maintained, it is also possible that

food availability and eating patterns were affected. Amidst an unsettled colonial social

climate and a significant increase in morbidity and mortality among Lamanai Maya, it is

postulated that Spanish demands for tribute negatively affected the health and nutrition of

Maya infants through economic pressures on their mothers (Chapter Two). Potential

physiological consequences include reduced breastfeeding, reduced weaning age (with

potential morbidity and mortality risks), and even, changes in population birth rates and

female survival, since extended nursing can reduce fertility and increase the time period

between conceptions.

Assuming colonial changes were significant enough to impact weaning behavior (i.e.,

breastfeeding duration) and children’s health, Historical period enamel Sr/Ca could

appear as a condensed version of Postclassic patterns. Several models are possible in this

case: 1) supplementation might have begun earlier, which would be reflected in earlier

enamel Sr/Ca increases, but was followed by continued long-term nursing; 2)

supplementation might have begun earlier, but was followed by a faster rate of breast

milk cessation (earlier weaning age), which would appear as a steeper slope graphically;

3) age of supplementation might have remained constant but the rate of food

supplementation increased (earlier weaning age).

139

In contrast, social conditions at Lamanai may have affected infant health by reducing

the consistency of available weanling foods (maize gruel). In this case, food

supplementation (Sr/Ca increase) may have been erratic or delayed because of seasonal

or occasional disruptions in maize production and distribution, as well as infant and

maternal illness.

In the colonial environment of epidemics and famines, it is likely that more Maya

mothers perished than during the Postclassic. In such cases, breast milk intake would

have ended abruptly and orphaned infants might not have had the fortune of a substitute

wet nurse. Immediate total reliance on weanling foods would characterize such infants

and would appear chemically as a substantial increase in Sr/Ca over a very brief period.

Such infants might be recognized as those with the steepest Sr/Ca slopes over time.

Considering that early nutrition has major repercussions for later survival, the ability

to reconstruct subtle dietary changes during weaning via LA-ICP-MS of enamel provides

an unprecedented detailed account of the transition from infant to adult diet. Application

of microsampling techniques preserves the general integrity of fossilized remains and

precisely captures the time-sensitive chemical data that is inherent in sequentially formed

enamel. More so than bone, teeth provide a hard tissue biography of ancient childhood

nutrition that is minimally affected by taphonomic processes and are rich reservoirs of

element composition clearly associated with dietary intake, which can be attributed to

known developmental age. Teeth are thus the ideal hard tissues for reconstructing the

weaning process among ancient populations.

140

CHAPTER 6

MATERIALS AND METHODS

6.1 Analytical Technique

This study broadens the range of bioarchaeological questions that can be asked of

human remains by utilizing Laser Ablation-Inductively Coupled Plasma-Mass

Spectrometry (LA-ICP-MS). Specifically, LA-ICP-MS analysis of ancient human

enamel is used to provide meaningful inferences for dietary intake during early

childhood, the period when teeth are formed. The ability of LA-ICP-MS to sample

enamel of known developmental age enables study of important life events such as the

timing of infant dietary transitions and their nutritional consequences. With this

technology, this research establishes a method of paleonutritional reconstruction that

addresses two key challenges in hard tissue analysis: 1) the isolation of chemical

composition to precise developmental age, and 2) minimal destruction of invaluable

human remains.

LA-ICP-MS involves the coupling of Laser Ablation (LA) sampling with Inductively

Coupled Plasma-Mass Spectrometry (or Spectroscopy) (ICP-MS), which is a technique

of multi-element analysis that quantifies element concentrations based on atomic mass to

charge (m/z) ratio. Laser ablation technology has been applied to two major areas of

research: 1) bulk analysis, which involves low spatial resolution (80-350 m crater

diameters) and 2) local analysis, such as this one, which has high spatial resolution (4-80

m crater diameters) (see Gunther et al. 2000).

141

In this study, enamel is microsampled by localized laser energy, rather than by total

acid dissolution. It offers several advantages over conventional methods of chemical

analysis, namely rapid, multielement and isotopic analyses, low detection limits (high

sensitivity), minimal sample preparation (and low cost), high spatial resolution, high

sample throughput capability, and importantly, for studies of archaeological specimens,

minimal sample destruction (Denoyer et al. 1991; Evans et al. 1995; Gray 1985; Kang et

al. 2004; Outridge 1996; Outridge et al. 1995; Perkins et al. 1991; Ward et al. 1992).

Like ICP-AES, ICP-MS is an ideal technique for the quantification of trace elemental

composition of biological tissues, environmental, geological and food samples.

To date, this technology has been effective in tracing environmental pollution, animal

habitat origins and migrations, human migration, hard tissue preservation, archaeological

materials provenance, element profiling, fetal and infant nutrition, and even forensic

science (Ward et al. 1992; Fuge et al. 1993; Wang et al. 1994; Evans et al. 1994, 1995;

Kang et al. 2004; Outridge et al. 1995; Cox et al. 1996; Outridge 1996; Watmough et al.

1997; Budd et al. 1998; Lee et al. 1999; Watling 1999; Belloto and Miekeley 2000;

Gratuze et al. 2000; Haverkort 2001; Prohaska et al. 2002; Goodman et al. 2003; Neff

2003, among others). Utilized materials for such studies include animal and human

bones and teeth, tusks and soft tissues, mollusks, fish otoliths (inner ear stones), scales,

tree rings, ancient pottery, gold, cannabis leaves and crime scene artifacts.

Briefly, laser ablation sampling entails directing a high energy pulsed laser beam

(LA) onto the surface of a solid sample housed in a vacuum-sealed chamber. Upon

contact, the solid sample becomes vaporized, and this ablated material is then swept with

a flow of argon gas into an inductively coupled argon plasma (ICAP) torch. Here, single

142

charged ions are produced from the vaporized sample by excitation, at temperatures

between 8000K and 10,000K, and then extracted by the mass spectrometer (MS) for

detection. A quadrupole mass filter in the mass spectrometer separates analytes

according to atomic mass-to-charge (m/z) ratios (see Denoyer et al. 1991; Gray 1985;

Ward et al. 1992). Visually, element abundance across the sampled transect can be

reported as a line graph with a y-axis of “element intensity”, and an x-axis of “reading #”

or “time in seconds”, which can be correlated to distance on the tooth (see Figure 6.1).

Figure 6.1 Tooth cross-section indicating correlation of laser ablation position,

development age and enamel Sr/Ca intensity ratio

143

While ICP-MS has been widely used to analyze samples prepared by acid digestion,

its coupling with LA technology represents a novel approach to sampling. In total,

combining these technologies takes advantage of the benefits and capabilities of both:

localized microsampling and surface profiling by LA and extremely sensitive,

quantitative, multielement analyses by ICP-MS.

Firstly, laser ablation sampling eliminates the difficulties involved with enamel

separation that characterize “crude” techniques such as scraping and drilling, which often

also gouge dentine material. As well, it avoids questions of quantity and developmental

age of sampled enamel that plague acid digestion techniques. Further, both physical and

acid removal of enamel can result in combined sampling of both contaminated surface

enamel and more intact interior enamel. In creating an ablation trench only 50 m wide

and deep, any limitations with enamel collection are strictly due to operator error or

problems with dental material identification.

Sampling of enamel by laser ablation requires minimal sample preparation, as the

material can be analyzed practically intact. The main challenge with human dental

material involves preparing an internal enamel plane that is as level and developmentally

complete as possible, which is generally along the central axis of teeth. Compared to

methods of chemical analysis that involve acid digestion, the preparation for laser

ablation sampling entails minimal contamination risk.

LA-ICP-MS also diminishes the degree of polyatomic interference that can arise in

conventional solution nebulization (SN)-ICP-MS. “Dry (argon) plasma” used in LA-

ICP-MS reduces the likelihood of the formation of 40

Ar16

O+,

15N

16O

+ and

16O2H

+, which

can result from the interaction of water and HNO3 acid (Durrant 1999).

144

Significantly, the application of LA microsampling technology reveals a level of

intra-tooth variation that is not captured by other methods. The coupling of laser ablation

sampling to ICP-MS is highly amenable to dental analysis as it can “read” chemical

markers across the tooth surface, producing a “map” of chemical signatures specific to

tooth location (see Figure 6.1). Due to the tree-ring-like nature of teeth, which allows

association of tooth location with developmental age (see Massler et al. 1941), chemical

profiles produced by LA-ICP-MS disclose a wealth of data documenting health and

nutrition that can be attributed to specific periods, e.g., fetal development or infant

weaning. The nature of health and nutrition during these periods of childhood are

particularly significant and predictive of future adult survival (see Cook and Buikstra

1979; Goodman and Armelagos 1988; Goodman et al. 1980, among others).

In the words of Outridge and co-workers (1995: 167):

LA-ICP-MS and other microprobe techniques are thus revealing that the

heterogeneity of metal distribution at microspatial scales is no less of a sampling

design problem than for macroscale entities such as forests, oceans, etc., and entails

similar types of statistical considerations, data management, and visual

representation.

6.2 Technological and Methodological Challenges

While LA-ICP-MS has great potential, there remain several limitations to its effective

use on biological material. To date, (LA) ICP-MS is only semi-quantitative due to the

unavailability of matrix-matched standards (see Amarasiriwardena et al. 1997; Evans et

al. 1994; Outridge et al. 1995). Results of quantitative analyses with a range (or

accuracy) of +/- 30-50% are considered semi-quantitative (Amarasiriwardena et al. 1997),

145

while determinations with accuracy of less than +/-10% are quantitative (Ahrens and

Taylor 1961; Wang et al. 1972).

Lacking a suitable reference standard for enamel, external standards (e.g., glass NIST

610, 612, 614) have been used to calibrate LA-ICP-MS results of teeth and carbonates

(e.g., Durrant 1999), but this is still limited by a matrix mismatch between hard tissue

apatite and glass (see below).

Difficulty with calibration led Cox and colleagues (1996: 256) to conclude:

As no suitable standard reference materials are currently available for teeth, and in

view of the requirement for qualitative data and for inter-sample comparison rather

than absolute quantitation, we suggest that the principle of element/element ratioing

be adopted.

Likewise, Ward, Durrant and Gray (1992: 1145) state: “as it is not known in advance

whether or not internal standardization is necessary, its use may be advisable as a matter

of policy”. In this case, calcium is an appropriate major element. Budd and colleagues

(1998) maintain that, owing to the slight effect of diagenetic substitutions on the

comparatively elevated level of calcium in hard tissues, calcium provides the best internal

standard for such chemical analyses.

According to Denoyer (1992), if matrix-matched, or internal standards are used, an

improved accuracy, or range, of +/-20-50% is possible for chemical determinations with

LA-ICP-MS. Outridge and colleagues (1995) estimate that with internal standards and

optimal instrumental conditions, the analytical precision of LA-ICP-MS can be less than

10% for elements between 0.1 and 1 ppm, and less than 5% for elements with abundance

exceeding 1 ppm, such as strontium. While still semi-quantitative, its application to hard

tissue analysis remains worthwhile because normalizing with internal elements provides

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invaluable relative concentration data. In this study, strontium levels will be interpreted

relative to simultaneously collected calcium abundance. As calcium is present in the

enamel matrix at high, relatively stable levels, it is an excellent choice for an internal

standard (see Cox et al. 1996).

Recent research utilizing LA-ICP-MS has focused on improving quantification

procedures, such as matrix-independent calibration methods using external solid

reference materials, which have increased in number (see Gunther et al. 2000). Gunther

and colleagues (2000: 4) note that with improvements in calibration and internal

standardization, LA-ICP-MS can yield accurate results between +/- <5 to 25% for

element concentrations.

The use of external standards is hampered by matrix differences, however. In

particular, the efficiency of laser ablation sampling is poor for glass discs (NIST), which

are often used for dental calibration, compared to pressed powder carbonate materials

(Bellotto and Miekeley 2000; Durrant 1999). Under the same laser conditions, crater

shape, depth and morphology will differ significantly between glass and carbonates,

resulting in distinct ablated masses and element results (Bellotto and Miekeley 2000).

Glass standard calibration curves will have lower sensitivity and there will be an

overestimation of trace element concentrations in carbonate matrix samples (Bellotto and

Miekeley 2000: 638).

Quantification of LA-ICP-MS results remains a research concern because of several

factors: uneven sample ablation, non-representative sub-sampling, differences in

transport efficiencies of material components to the plasma and, importantly, lack of

147

suitable matrix-matched standards for calibration (Durrant 1999; Bellotto and Miekeley

2000; Gunther et al. 2000)

Additional challenges include lack of homogeneity within an increment of analyte

(Outridge et al. 1995) and non-uniform ablation sampling (Evans et al. 1995). Non-

uniformity of samples is either due to variable amounts of tooth material vaporization

(due to tissue density or laser intensity), or differential amounts entering the sample

stream (Evans et al. 1995). Watmough and colleagues (1997) observed non-uniformity

for various types of wood, calling for standards specific to the analyte. It is assumed such

differential ablation is due to variations in material composition and density, and if so,

this has significant implications for LA-ICP-MS of human teeth. However, in this case,

normalizing with calcium resolves some issues of differential sampling (variation).

Fortunately, preliminary results of laser ablations done within growth bands of an

ancient canine suggest that there is general elemental homogeneity (Goodman and Song,

unpublished data), which has also been observed in deciduous teeth (Dolphin et al., in

press; Goodman et al. 2003; Kang et al. 2004). Nonetheless, it is believed that the

advantages of minimal contamination, tooth preservation and precise enamel sampling

far outweigh the possibility of sampling anomalous enamel. In general, it is widely

believed that enamel within the same growth band exhibit compositional homogeneity.

Recent developments in LA-ICP-MS research include use of laser systems with

shorter wavelengths (1064 nm, as opposed to 266 nm used in this study and many

others); UV gas (excimer) lasers; changes in laser pulse to pulse stability and the optical

arrangement of beam transfer optics; experiments with sampling instrumentation (e.g.,

ablation cells); mechanisms of sample transport (e.g., mixed gas sample introduction);

148

ICP-MS measurement (detector) efficiency; direct solution ablation; and improvements

in quantitative analysis, among others (see Gunther et al. 2000). Such research has been

geared toward improving sensitivity and sample transport, stability of ICP conditions,

reducing element fractionation (“non-sample related variation of the analyte response

during ablation” [Gunther et al. 2000: 4]) and simplifying instrumentation set-up and

operation.

As a result, LA-ICP-MS results (i.e., analyte sensitivity and limits of detection) have

been found to be influenced by crater dimensions (diameter to depth ratio), energy

density, repetition rate, laser focal point (rather than wavelength) and background noise,

which all affect the amount of ablated and transported material to the ICP and are

important factors in elemental fractionation (see Durrant 1999; Gratuze et al. 2001;

Gunther et al. 2000).

Recent research suggests that variation in ablation yield, decreased signal and

elemental fractionation can be limited by 1) applying raster ablations, rather than single

spots; coupled with 2) relatively large crater size (100 μm) (Neff 2003); 3) collecting data

in three or more different ablation runs (Gratuze et al. 2001); and 4) use of a 213 nm

wavelength laser instead of 266 nm (Gunther and Hattendorf 2001; Jackson 2001). Still,

it is a challenge to distinguish whether the sources of fractionation are related to the

ablation process, the transportation process and/or the ICP excitation and ionization

process (Gunther et al. 2000).

149

In surveying the literature, tremendous variation exists in the preparation and

collection of dental material for chemical analysis. This variation includes: 1) the type

of mechanical separation and localization of dental tissues (e.g., burr drilling, chipping,

scraping); 2) choice of teeth, and whether they are analyzed individually or together; 3)

region of dental tissue sampled, since surface enamel and root dentine exhibit higher

levels of contaminating elements such as lead; 4) duration and concentration of acid

solutions used to clean teeth; and 5) analytical technique employed, which has resulted in

diverse findings.

A significant source of variation concerns sample decontamination. Preparation of

hard tissue samples requires utmost care because of the present understanding of

diagenesis. Evidence by researchers such as Ambrose (1990), DeNiro and Epstein

(1981), DeNiro and Hastorf (1985), Farnsworth et al. (1985), Kyle (1986), and Lambert

et al. (1979, 1982, 1985), among many others, have demonstrated that post-mortem

contamination of hard tissue elements and stable isotopes can significantly alter chemical

values, and consequently, dietary reconstruction. Diagenetic mechanisms include

deposition, leaching or substitution of elements and other components (lipids, carbonates,

humic acid), as well as extraneous factors that degrade overall tissue composition (soil

pH, water solution, temperature).

An initial assessment of chemical integrity can be based on overall appearance (see

Chapter Three), but such discrimination should only be applied site-specifically, since the

gross, morphological appearance of bone is not necessarily a good indicator of chemical

integrity (e.g., Klepinger et al. 1986). Diagenetic change also tends not to be a

150

predictable function of duration of interment (Klepinger et al. 1986) (although see

below).

In teeth, gross structural integrity, as reflected in intact crowns, consistent ivory color,

minimal attrition and disease (caries, hypocalcification) will be more likely associated

with good chemical preservation. Post-mortem alteration of dental organic material is

more time-dependent than apatite crystallite diagenesis (Carlson 1990: 545). As dental

enamel is predominantly inorganic, it is the least susceptible to post-burial contamination,

particularly regarding aluminum, iron, strontium and barium (Kyle 1986; Parker and

Toots 1970, 1980). The only limitation with dental enamel is that its composition will

only reflect trace elements circulating at the time of enamel formation (childhood).

In order to circumvent the effects of diagenesis on fossil remains, especially for the

purposes of chemical analysis, numerous methods have been devised to remove

contaminating substances prior to analysis. The simplest method, as described by

Szpunar et al. (1978) involves simple brushing and washing with distilled/deionized

water. This fundamental process only removes clinging surface contaminants, as does

ultrasonic cleaning in high-purity water (e.g., Millipore Alpha Q H2O) (Budd et al. 1998;

Wright and Schwarcz 1998).

Chemical methods have been developed to cope with pervasive contamination of hard

tissues. Extraneous elements have been removed with washes of 1N acetic acid (Krueger

and Sullivan 1984; Lambert et al. 1990; Sillen 1986; Sullivan and Krueger 1981); ethyl

alcohol (Wright 1990); hydrochloric acid (HCl) (Gulson and Wilson 1994; Rose 1977,

1979); nitric acid (HNO3) (Gulson and Wilson 1994; Song and Stillman 1998); and

151

hydrogen peroxide solutions (H2O2) (Budd et al. 1998; Gulson and Wilson 1994; Song,

present analysis), among others.

These chemical procedures remove substantial diagenetic material from hard tissues,

but they also entail several consequences, such as: 1) the removal of biogenic Na, Mg and

K that are present on the surface of bone crystals (see Lambert et al. 1990); 2) deposition

of calcium salts on the surface of tooth sections, as the result of hydrochloric acid washes

(see Wright 1990); and 3) removal of significant biogenic bone (by 1N acetic acid)

(Krueger and Sullivan 1984; Sullivan and Krueger 1981).

This can be contrasted to the physical abrasion method, which does not affect

biogenic levels of aluminum, iron, magnesium, potassium, sodium or zinc. Overall, a

combination of physical abrasion and mild chemical washings (e.g., acetone, hydrogen

peroxide) is probably the best procedure for removing diagenetic additions (see Lambert

et al. 1990). Fortunately, none of the abovementioned methods were found to deplete

biogenic calcium or strontium, which are important elements with respect to diet.

Despite appeals for a reliable standardized preparation methodology (Boyde et al.

1978; Carlson 1990; Fergusson and Purchase 1987), there is as much variation as ever

regarding cleaning procedures. For histological studies, in particular, non-standardized

variations in preparation methods have notable consequences. Significantly, there can be

confusion with comparing histology and structural patterns of teeth, which can appear

different or similar depending on preparation technique (see Carlson 1990; Wright 1990).

152

6.3 Materials and Methods

The teeth were collected by the author from the Department of Anthropology at Trent

University, Peterborough, Ontario, Canada, where the bulk of Lamanai human remains

are currently housed (others remain in storage in Belize). Sample collection involved

sorting through all Postclassic and Historic period individuals at the university, which

amounts to approximately 106 Postclassic and 131 Historic period individuals. The

Lamanai human remains are in good condition for Lowland Maya burials, particularly the

dental remains.

Based on several criteria, one intact permanent mandibular or maxillary canine was

collected from each suitable individual, and the relative macroscopic “health” of each

tooth was assessed for the purposes of data completeness (see Appendix A). Permanent

canines are utilized because they are among the longest developing teeth in the human

dentition, with enamel forming shortly after birth to approximately five or six years of

age. As a result, they record life history for almost the entire period of breast milk

consumption and provide useful comparative data for tracing the subtle changes of a

prolonged dietary transition.

The teeth derive from adults of both sexes, as well as children of varying ages who

did not survive to adulthood, but whose canine crowns are complete. The sample is rich

with the dental chemistry histories of individuals with varying adaptive abilities, dietary

intakes and development. Note, however, that due to the requirement for: 1) a

completely developed canine crown (with cemento-enamel junction present), and 2)

minimal to moderate dental attrition, children who died younger than five to six years of

age and older adults with highly attritioned teeth are not included in this study.

153

Obviously, this limitation excludes individuals from two demographic extremes:

1) the least “successful” individuals who were not fit enough to survive early childhood

(younger than 5-6 years), and 2) the most advantaged individuals, or those older adults

with heavily worn teeth who probably experienced the greatest benefits to health and diet

in early life.

Yet, inclusion of complete canines from individuals who died in later childhood, i.e.,

older than 5 years of age (25% of total sample), means that some individuals who

experienced greater health and/or dietary stress are still considered in this analysis. (One

must remember that these disadvantaged children may have had atypical diets associated

with their poor health.) Overall, it is felt that the sample adequately represents the

general health and dietary conditions of the population in prehistoric and colonial times.

Age and sex information for each individual was derived from the Lamanai database

at Trent University [evaluations by Drs. H. Helmuth (Trent University) and C.D. White

(University of Western Ontario)], as well as the author’s general assessment of the dental

and skeletal remains during sample collection.

To maintain an adequate representation of dental remains for the Lamanai population,

canines were only collected from individuals with at least one other permanent canine, so

that such teeth are still available for future research. Collected canines are both

mandibular and maxillary. Only teeth with non-existent or minimal surface cracks

(overall good structural integrity) were chosen. Consequently, deeply filed or inlaid teeth

were not considered, as were many teeth that were fragmented due to poor post-

depositional and post-excavation preservation.

154

In total, only canines from 26 Postclassic and 34 Historic period individuals were

deemed appropriate for this analysis (see Table 6.1).

Table 6.1 Sample Breakdown

Time Period

Sub-Adults

Females

Males

Indeterminate

Adult

Total

Postclassic

6 (5 maxillary,

1 mandibular)

12 (5 maxillary,

7 mandibular)

7 (2 maxillary,

5 mandibular)

1 (1 mandibular)

26

Historical 9 (4 maxillary,

5 mandibular)

13 (7 maxillary,

6 mandibular)

12 (7 maxillary,

5 mandibular)

0 34

Once in Amherst, the teeth were further examined and prepared at the School of

Natural Science, Hampshire College. Macroscopic analyses of the teeth were undertaken

with the unaided eye, using an electronic sliding caliper for measurements of tooth

dimension and surface defect location. Observations include total crown height, degree

of dental attrition and calculus build-up, caries prevalence and the presence of any

developmental defects of enamel, namely hypocalcification discoloration and enamel

hypoplasia (see Appendix A). Enamel defects and the time of their formation are also

compared by temporal period, age (children vs. adults) and sex in Appendix A.

Macroscopic dental features were examined for the purpose of assessing dental health

patterns related to diet, health and hygiene. At this stage, surface calculus was carefully

removed to facilitate crown and defect measurements and to prepare the teeth for

cleaning (see below). Considering the potential for future chemical analyses of the

calculus, all such residue was retained and stored in labeled Ziploc bags.

155

6.4 Sample Preparation

In preparation for LA-ICP-MS, the teeth underwent a four stage cleaning process

according to the specifications of Drs. D. Amarasiriwardena and A.H. Goodman

(Hampshire College). This process is believed to maximize organic and inorganic

contaminant removal, while also preserving the innate chemical composition of the

material. The decision not to use certain strong acids (e.g., acetic, nitric, hypochloric) to

rinse or wash the teeth was based on the potential risks for ionic interference, i.e.,

leaching and substitutions.

Additionally, in order to minimize contamination, all glassware utilized for cleaning

was washed and rinsed in 18 M. cm (distilled and deionized) water, as were plastic

utensils. Other utilized materials were new, and in the case of kimwipes, a cellulose-

based, nonabrasive, lint- and static-free “delicate task wipe”, are deemed non-

contaminating for the purposes of ICP-MS analysis.

Initial cleaning involved manual brushing of the teeth with a new medium bristle

nylon toothbrush and 18 M. cm water. The teeth were subsequently soaked in 10 mL

disposable plastic micro beakers filled with 18 M. cm water for two days, so that any

adhering residue was loosened from the teeth. Two days later, the teeth were soaked in

new beakers filled with a 1% (w/w) papain solution for two days. Papain is a proteolytic

enzyme derived from papaya that breaks down protein and lipids. The beakers were

covered with plastic wrap to protect the teeth from air-borne contaminants.

Once removed from the papain with plastic tweezers, the teeth were thoroughly

rinsed several times with 18 M. cm water. They were then given a 30 second bath in a

3% (v/v) H2O2 solution for additional removal of organic material. Each dip was

156

carefully timed to avoid etching of the teeth and the hydrogen peroxide solution was

changed after every fifth tooth. Following each dip, the teeth were thoroughly rinsed

with 18 M. cm water. They were soaked a second time in new plastic beakers filled

with 18 M. cm water for one day. After removal from the water, the teeth were dried in

new beakers covered with kimwipes for one day.

After the four-stage, six-day, cleaning process, the teeth were prepared for

embedding. Using plastic tweezers, and holding the teeth by their roots, the teeth were

positioned in new plastic embedding containers so that they stood upright on their root,

with the occlusal surfaces facing up. The root tips were adhered to the base of the

container by heated glue. To facilitate subsequent cutting of the resin block, the teeth

were oriented with the labial-lingual plane parallel to the sides of the square container.

Once set, the containers were filled with Buehler Epoxide Resin (Lakebluff, IL, USA)

(five parts Epoxide Resin [bisphenol-A epoxy resin, N-butyl glycidyl ether] to one part

Epoxide Hardener [alkyl ether amine, diethylenetriamine, phenol, triethylenetetramine]),

a plastic resin that is considered non-contaminating for trace chemical analytical

purposes. The containers were then placed in a vacuum for approximately twenty

minutes to minimize air pockets in the resin as it set. They were left for two days to cure

and harden.

The last stage of tooth preparation involved cutting the resin blocks. Here, an Isomet

slow-speed saw was used with a new Buehler copper diamond-tipped disk blade. To

remove contaminants from manufacturing and packaging, the blade was rinsed with

acetone and 18 M. cm water prior to use. 18 M. cm water was also used throughout

the cutting process to lubricate the blade. The resin block was positioned so that the teeth

157

were cut at the midline along the labial-lingual plane. However, in some cases, when

there was uneven occlusal wear or the presence of a surface crack, the tooth halves were

divided unevenly, i.e., not along the midline. In such cases, as for all teeth in general, the

teeth were cut at the best position to ensure maximum enamel exposure in the sectioned

block.

At this time, one thin section of tooth and resin was also removed adjacent to the first

dividing cut and glued to a microscopic glass slide. According to the calibration on the

saw, this thin section is approximately 250 m thick. Thin sections of each tooth were

cut for the purposes of comparative histological analysis, which might aid in assessments

of nutritional status (see Marks and Rose [1985] for methodology).

Prior to laser ablation sampling, the cut surface of one block half underwent another

rinse with 3% (v/v) H2O2, followed by a rinse with 18 M. cm water, to eliminate

surface contaminants. To prevent spreading and admixture of dissolved material on the

cut tooth surface, the hydrogen peroxide was carefully poured so as to just cover the

tooth, and left to set for approximately one minute. The peroxide was then briskly

shaken off the tooth and the block rinsed in 18 M. cm water.

Importantly, the potentials for contamination in the use of manual brushing, papain

soaks, hydrogen peroxide dips and embedding in epoxy resin are minimal. ICP-MS

analysis of resin also indicates that there is minimal potential for contamination of the

embedded tooth. In general, the resin contains a thousand times less concentration of

relevant analytes present in dental material (A.H. Goodman, personal communication,

2000).

158

6.5 A Protocol for LA-ICP-MS Analyses of Human Dental Enamel

The operation of the LA-ICP-MS entails: 1) placing the embedded tooth section in

the laser ablation sampling chamber (“sample cell”), which is secured to a rotating

platform with double-sided tape; 2) orienting the tooth so that the ablation path is

horizontal at 180o; 3) determining the appropriate settings for the laser and mass

spectrometer in the computer program that operates the device; and finally 4) setting the

coordinates for the laser's path along the tooth surface. Analyses are carried out using the

time resolved analysis (TRA) mode, in which data is collected in discrete time segments

(ion counts/second) while the sample is continuously ablated at a constant rate (Lee et al.

1999; Montgomery et al. 1998).

As the laser can only sample material across a straight line path, several separate

transects angled to follow the tooth’s curve from occlusal tip to cervix, near the cemento-

enamel junction, were ablated (see Figure 6.2). Thus, ablated trenches vary in length

based on the morphology of each tooth, but most teeth have two to three connecting

ablation lines. Due to ionic incorporation of surface elements during life and/or post-

mortem, particular care was taken to ablate samples from inner enamel only.

Figure 6.2 Position of laser ablation trenches along secondary canine crown

(with approximate ages of enamel development indicated)

159

For this analysis, laser ablation sampling was the “line” ablation type, which samples

enamel across a continuous line at a constant rate (20 m/sec). All canines were ablated

across the entire length of labial enamel to ensure that enamel was collected from all

periods of crown development, from approximately six months to five or six years of age.

Labial enamel was ablated because of two factors: 1) enamel is thicker in this region

and thus, easier to sample and observe histologically, and 2) surface absorption of ions

(contamination) is less likely. As noted previously, despite its inorganic composition,

surface enamel is prone to ionic exchange with several elements in the oral environment,

most notably lead and fluorine in contemporary times. Surface absorption of contaminants

is most pronounced on the lingual surface of teeth and surrounding the neck due to their

increased contact with saliva and plaque (Carroll et al. 1972; Purchase and Fergusson

1986). Additionally, with respect to lead, higher levels characterize the amelodentinal

region and root dentine compared to coronal dentine (Malik and Fremlin 1974).

In archaeological teeth affected by diagenesis, strontium values in dentine are also

inflated relative to enamel, which tends to be largely homogeneous in strontium

concentration (Montgomery et al. 1998). In total, owing to the thicker nature of labial

enamel, sampling within an inner region considerably distant from (less) potentially

contaminated surface enamel is more feasible and preferable.

Table 6.2 outlines the LA-ICP-MS operating parameters utilized in this investigation.

The instrumentation includes a Perkin Elmer Sciex, Elan 6000 ICP-MS (Perkin Elmer

Instruments, Shelton, CT, USA) coupled to a CETAC LSX-100 Laser Ablation System

(frequency quadrupled Nd:YAG [neodymium-yttrium aluminum garnet] laser) (CETAC

Technologies, Omaha, NE), operating at 266nm in (UV) wavelength. For adequate

160

sampling of enamel material, an energy level averaging around 0.9 -1.0 mJ was required

for the laser (S. Keydel, personal communication, 2000).

Table 6.2 LA-ICP-MS Operating Parameters

Laser Ablation and ICP-MS Operating Parameters

Laser Ablation Operating Parameters:

Laser Type Nd: YAG

Laser Mode Frequency quadrupled 266 nm UV,

Q –switched mode

Repetition Rate/Hz 10

Laser Energy/mJ 0.6-1.1

Sampling Scheme Raster

Scanning speed/μm.s-1

20

ICP-MS Operating Parameters:

Forward power/ kW 1

Ar gas flow rates/L. min-1

Coolant 15

Auxiliary 1.2

Nebulizer gas 0.9

Measurement conditions:

Dwell time/ms 25

Resolution high

Sweeps/reading 1

Readings/replicate 5600

Number of replicates 1

Isotopes measured (m/z) 137

Ba, 138

Ba, 43

Ca, 44

Ca, 63

Cu, 65

Cu, 57

Fe, 24

Mg, 25

Mg,

55Mn,

206Pb,

207Pb,

208Pb,

78Se,

82Se,

86Sr,

88Sr,

64Zn,

66Zn

Internal standard (m/z) 43

Ca

161

Considering the operating parameters, the energy level chosen for the laser ablation

device was 13, with a pulse rate of 10 and an ablation speed of 20 m/second. These

settings produced an ablated trench measuring approximately 50 m wide and deep.

Only microgram quantities of enamel were sampled from each tooth.

Throughout, the ablation process (and element behavior) was viewed in real time

through a 20x video monitoring system (see Figure 6.3). This attached monitor and

microscopic camera enabled identification of different dental tissues and establishment of

the ablation path prior to analysis. Observations were made during each ablation process

and were recorded on a standard form prepared by the author (see Figure 6.4). Recorded

details include operating parameters, fluctuating energy levels, ICP reading numbers for

each ablation, relative location, ablation lengths (measured by the LA device and

computer software), and reading locations of distinct enamel features (e.g., defects,

cracks, proximity to dentine and cemento-enamel junction). A sketch of each tooth

section and ablation locations accompanied each data sheet on the reverse side.

Figure 6.3 Schematic of instrumentation used in LA-ICP-MS

(from Denoyer et al. 1991: Fig. 1)

162

Figure 6.4 Example of LA-ICP-MS recording sheet used in this analysis

163

Once ablated, the vaporized enamel was swept from the sample chamber to the

plasma source with a flow of argon gas. In the plasma, the sample was atomized, ionized

and then transported to the mass spectrometer for quantification. As befits the

capabilities and advantages of ICP-MS technology, multiple elements were quantified.

In addition to strontium (86

Sr, 88

Sr), these elements include barium (137

Ba, 138

Ba), calcium

(43

Ca, 44

Ca), copper (63

Cu, 65

Cu), iron (57

Fe), lead (206

Pb, 207

Pb, 208

Pb), magnesium (24

Mg,

25Mg), manganese (

55Mn), selenium (

78Se,

82Se) and zinc (

64Zn,

66Zn). Quantification of

these isotopes were deemed appropriate for the purposes of dietary and nutritional

reconstruction, reduced polyatomic interference (D. Amarasiriwardena, S. Keydel, P.

Outridge, personal communications, 2000, 2001), as well as future studies on pollution

(for instance, lead may be useful in tracing possible environmental exposure during the

production of lead-glazed ceramics [e.g., Tunstall and Amarasiriwardena 2002]).

As stated earlier, the LA-ICP-MS analytical approach is ideally suited to dental

analyses as it produces a “map” of chemical signatures specific to tooth location and

developmental age. Thus, interpretation of the chemical blueprint of sampled enamel is

the final stage of LA-ICP-MS analysis. This involves statistical comparison of strontium

levels relative to calcium over time (tooth location). Calcium (e.g., 43

Ca) is an

appropriate normalizing element since it is present in the enamel matrix at relatively

stable, high, levels.

Upon completion of this investigation, dental remains will be returned to Trent

University either in embedded form, or disengaged from the resin mold and thin section.

In this case, analyzed teeth can be returned to their original state by heat removal of the

plastic resin and gluing of the thin section within the cut tooth halves (it is suggested,

164

however, that the thin section is maintained for the purposes of a histological database

and future analyses). Other than a minuscule trench of ablated enamel (approximately 50

m wide) in the center of the tooth, glued teeth appear complete and remain available for

future research.

6.6 LA-ICP-MS Observations

In light of the sparse application of laser ablation sampling to human tissues, several

features of LA-ICP-MS are worth mentioning. First, in an analysis that involves raster

(continuous) laser sampling of enamel along entire crown lengths, substantial numerical

data is generated. For instance, with a canine crown measuring 11 mm, the approximate

average unworn crown height of Lamanai canines (Appendix A: Table A.1), a continuous

laser ablation produces around 800 readings per element (see Appendix B Tables).

Quantification of multiple elements and several isotopes of each element results in large

data files for every ablation.

During the process of laser ablation, ICP-MS quantification of elements is recorded

for both the periods of sample ablation as well as during non-sampling, when argon gas

continues to flow. Graphically, each phase of operating the LA-ICP-MS can be

distinguished by distinct Sr/Ca patterns (see Figure 6.5).

The periods of closed chamber non-sampling when argon gas continues to flow

through the ICP-MS torch are clearly recognizable by the significantly higher Sr/Ca

ratios (Figure 6.5: phase “A”). This ratio is the result of relatively low Ca readings,

rather than elevated Sr values. (With enamel ablation sampling, significantly higher Ca

values dramatically reduce the Sr/Ca ratio.) Although the argon gas used in ICP-MS is of

165

a high purity, it is clear from Figure 6.5 that the gas blanks are not completely uniform,

with some variation evident. Slight variations in the very low total Ca intensity relative

to Sr intensity in argon gas account for the fluctuations.

Figure 6.5 Graph illustrating distinct patterns in Sr/Ca during LA-ICP-MS

Periods of actual enamel ablation are distinguished by a substantial drop in Sr/Ca due

to significantly higher Ca values (phase “B”). As a result, the readings during initial

enamel sampling are often significantly higher than Sr/Ca values of subsequent enamel,

since they are actually residual “argon blank” readings. Care has been taken to eliminate

unusually high initial readings for the data analysis and presentation, but in some cases,

the initial periods of enamel development are still marked by high Sr/Ca values that

diminish shortly thereafter (see Chapter Seven).

A

Fluctuations in Sr/Ca during the entire process of LA-ICP-MS

0.00

0.50

1.00

1.50

2.00

2.50

0 200 400 600 800 1000 1200

Reading #

Sr/

Ca

ra

tio

------------- Dental Enamel ---------------

Argon Blank Argon Blank

Sample Chamber Open

A

B C

166

A third phase of activity during LA-ICP-MS can also be identified in Figure 6.5

(phase “C”). When the sample chamber is open to re-position tooth sections for

additional ablations, and argon gas continues to flow, Sr/Ca ratios appear slightly

enhanced compared to readings when enamel is being ablated (“B”). However, they are

still significantly reduced compared to periods of non-sampling when the chamber is

closed (“A”).

Factors that affect the sampling of material to the ICP torch (i.e., intensity of the

element signal) and quantification of elements include sample hardness, sample position

in the laser chamber, whether or not it is level, as well as instrumental drift in the ICP-

MS over several hours or days (see Gratuze et al. 2001; Neff 2003). Instrumental factors,

such as decreased signal (sensitivity) and elemental fractionation over time, are attributed

to thermal processes at the ablation site, as well as changes in the aspect ratio of the

ablation crater (Gunther and Hattendorf 2001; Jackson 2001).

To diminish such effects, Gratuze and colleagues (2001: 646) suggest collecting data

in three or more different runs, but this was not possible in this study due to the thinness

of enamel in sections of labial crown near the CEJ. Neff (2003: 24) also suggests that

raster, or continuous lines ablations, rather than single spots, and ablations of relatively

wide crater width (100 μm) can reduce the problem of decreased signal and fractionation.

This study adopts the raster mode of sampling, with crater widths restricted to

approximately 50 μm (microns), because a wider ablation risks sampling of dentine in

areas of thin labial enamel (i.e., CEJ third). A crater width of 50 μm is appropriate for

this paleodietary analysis, however, and ICP-MS results of Lamanai canines indicate that

signal strength was not compromised during ablations.

167

6.7 Laser Ablation Details for Lamanai Canines

The following photograph illustrates an ablated Lamanai canine section with multiple

ablations indicated. A superimposed micrometer scale provides measurements of each

ablation.

Figure 6.6 Photograph of ablated tooth section and micrometer scale

(extrapolated crown tip and separate ablations indicated in black)

Periods of crown development covered by each ablation are based on the relative

lengths of laser ablations and enamel not ablated near the cusp tip and cemento-enamel

junction, compared to dental standards outlined in Appendix A. As illustrated in Figure

6.6, measurements are based on photomicrographs of ablated teeth and a micrometer

glass scale calibrated to 20 μm (0.02 mm), which were obtained with a NIKON 9000

168

digital camera and LEICA binocular microscope at 16x magnification. These figures are

generally greater (some are lower) than measurements obtained during laser ablation with

CETAC Laser Ablation operating software (CETAC, Omaha, NB), but they are not

significantly different, i.e., less than 5 % higher on average (3.64%). Similarly,

Haverkort (2001) has found slight discrepancies between measurements of laser ablation

tracks made from SEM images and software-generated distances based on scan duration

and scan speed, which is attributed to slight distortions in the SEM images.

Photographic evidence was used since measurements for unablated enamel near the

cemento-enamel junction and at the cusp tip could not be measured by the laser ablation

device and software. In particular, enamel missing from the cusp tip (the initial period of

crown development) had to be estimated in worn teeth by extrapolating a cusp curve on

the actual photograph (see Figure 6.6).

Based on photographic measurements, Tables B.1-4 in Appendix B outline the

ablation details for all Lamanai teeth analyzed in this study. Tables are grouped into

maxillary and mandibular teeth for consistency of enamel developmental period and the

“ages” (in years) represented in each ablation. Mandibular and maxillary teeth are

generally equally distributed in both samples and between age and sex cohorts:

Postclassic maxillary canines = 5 subadults, 5 females, 2 males; Postclassic mandibular

canines = 1 subadult, 7 females, 5 males, 1 adult unknown sex; Historical maxillary

canines = 4 subadults, 7 females, 7 males; Historical mandibular canines = 5 subadults, 6

females, 5 males.

169

6.8 Data Analysis

Initial organization of the data involved conversion of the raw data (intensity vs.

reading number) from PE Elan Software to Microsoft Excel files. Background gas 86

Sr

values (averaged for each ablation) were then deducted from the original 86

Sr intensity

readings for each tooth. High purity argon gas acts as the medium in which ablated

enamel is delivered to the ICP-MS for semi-quantification and it contains minor amounts

of trace elements. Argon gas blank values were recorded when the laser was not firing,

i.e., in between ablation runs, and range from approximately 2-20% of 86

Sr values

detected in enamel during laser sampling.

Next, as there is no suitable matrix-matched standard, 86

Sr readings were normalized

against 43

Ca values (minus argon gas 43

Ca) at each count of the ablation raster, producing

a Sr/Ca ratio, which is the basic unit of analysis in this investigation. The majority of

86Sr/

43Ca values for permanent canine enamel lie between 0.02-0.14 in this study (see

Chapter Seven). [While not available to this study, LA-ICP-MS data processing can be

simplified by implementation of the LADA (Laser Ablation Data Analysis) program

created by B. Hazes (see Haverkort 2001). Among other functions, this Fortran program

subtracts gas blank values from sample measurement values, calculates Ca ratios and

provides basic statistics of select data sets (e.g., correlations between elements,

logarithms).]

Unfortunately, as this study examined specific isotopes of strontium and calcium, the

Sr/Ca values calculated in this analysis have no directly comparable data in the chemical

and paleodietary literature, which have either examined total Sr/Ca or 90

Sr.

170

One is reminded of Sillen and Kavanagh’s (1982: 69) statement:

This raises a difficulty with most of the available literature and reviews on

strontium. Since researchers were primarily concerned about fallout, they tended to

emphasize the distribution of 90

Sr and other radioactive isotopes1. While this

information is, in many cases, extremely useful, it should be kept in mind that these

studies were not designed with the intent of developing a method for the

investigation of paleodiets. Indeed, apart from any applications, a great deal of

basic research on the use of Sr/Ca ratios for paleodietary research remains to be

conducted.

Even now, much of what is known about strontium’s distribution, behavior and

incorporation in hard tissues is based on early studies of radioactive fallout in the 1950’s

and 1960’s. Among many diverse studies, important data often referenced in hard tissue

strontium research include Beninson and colleagues (1964); Bryant and Loutit (1964);

Comar and co-authors (Comar 1963; Comar et al. 1957), Lengemann (1960, 1963;

Lengemann et al. 1957); Lough and colleagues (1963); Rosenthal (1981); Spencer and

colleagues (1961); Thompson (1963); Turekian and Kulp (1956); Steadman and co-

authors (1958); and Wasserman (1963; Wasserman and Comar 1960; Wasserman et al.

1958, 1977).

The majority of strontium reference data concerns 90

Sr, but all radioactive and stable

isotopes of Sr have the same physical properties, including the accumulation in human

hard tissues as a substitute for calcium (see Chapter Four). The four stable isotopes of

strontium occur in the following natural abundance: 88

Sr (82.56%), 86

Sr (9.86%), 87

Sr

(7.02%) and 85

Sr (0.56%).

1 Radioactive 90Sr was discovered in the 1940’s during nuclear experiments for the development of the atomic bomb, which resulted

in the atmospheric dispersal of large amounts of 90Sr worldwide. It is one of fourteen radioactive isotopes of strontium and is a by-product of the nuclear fission of uranium and plutonium (Faure and Powell 1972). With a half-life of 29 years and a widespread

distribution due to weapons experiments, nuclear reactor waste, and industrial accidents (Chernobyl), it is an important radioactive

isotope in the environment.

171

In this study, 86

Sr is the focus of investigation, with 43

Ca used as an internal standard.

Mass spectroscopic interferences and mass abundances are important factors in

considering which isotopes to analyze. Here, 43

Ca is used because it is the least abundant

Ca isotope (0.14%), is not subject to polyatomic interferences and is also free from

isobaric interferences (D. Amarasiriwardena, personal communication, 2002). The

reduced abundance of this isotope provides a manageable, yet adequate, signal for

calcium.

Relative signal strength and (reduced) risk of interferences are also important factors

in choosing 86

Sr, though one notes that there can be an isobaric interference of this

isotope with 86

Kr if it is present as a trace contaminant in argon gas (D.

Amarasiriwardena, personal communication, 2004). Still, 86

Sr is considered a suitable

isotope for strontium analysis in teeth.

Permanent canine enamel 86

Sr/43

Ca ratios for 0.25 year intervals range between

0.014-0.179, with the majority lying between 0.02-0.14. Compared to hard tissue total

Sr/Ca data of other studies (Mays 2003; Sillen and Smith 1984), these values are higher

by orders of magnitude due to the relatively higher abundance of 86

Sr against 43

Ca,

compared to total strontium versus calcium (see Chapter Seven).

However, total Sr/Ca ratios can be derived from the 86

Sr/43

Ca values presented in this

analysis since the abundance of all naturally occurring isotopes of strontium and calcium

are known. Calcium has six naturally occurring isotopes, with the following natural

abundance in percentages: 40

Ca (96.941%), 42

Ca (0.647%), 43

Ca (0.135%), 44

Ca

(2.086%), 46

Ca (0.004%) and 48

Ca (0.187%). Taking into account the differential

172

abundance of 43

Ca (0.135% of total Ca) and 86

Sr (9.86% of total Sr) isotopes, one can

extrapolate total Sr/Ca values that are comparable to reference data (see Chapter Seven).

This analysis has focused on 86

Sr and 43

Ca isotopes for dietary reconstruction, but

other human hard tissue strontium studies have utilized different naturally occurring

isotopes, albeit for different reasons (dietary vs. environmental exposure). These include

88Sr (Goodman et al. 2003; Haverkort 2001) and

90Sr (Bryant and Loutit 1961; Rivera

and Harley 1965; Thompson 1963). For calcium, 43

Ca has also been used as an internal

standard by Imai (1992), Goodman et al. (2003) and Kang and colleagues (2004), while

Haverkort (2001) and Montgomery and others (1998) utilized 46

Ca in LA-ICP-MS

analyses of human teeth.

Comparing Sr/Ca ratios of different Sr and Ca isotopes reflects the dramatic extent to

which ratios can differ in absolute value. Based on a set of ablations from a single day

(5600 readings), including six full ablations of canine enamel, different ratio

combinations using 86

Sr, 88

Sr, 43

Ca and 44

Ca were compared. In ablated enamel, with

44Ca as the internal standard,

86Sr/

44Ca was, on average, approximately 14.5 times lower

than the standard ratio used in this study (86

Sr/43

Ca), reflecting the higher abundance of

44Ca. With

88Sr instead of

86Sr, normalized with

43Ca, the opposite is true, with the

88Sr/

43Ca ratio approximately 8.7 times, on average, higher than the standard ratio (due to

increased 88

Sr abundance). Using different isotopes for both elements (88

Sr and 44

Ca)

produced a more analogous ratio to 86

Sr/43

Ca, but even in this case, 88

Sr/44

Ca was

approximately 1.7 times lower than the ratio used in this analysis.

Figure 6.7 illustrates the four combinations using 86

Sr, 88

Sr, 43

Ca and 44

Ca from one

enamel ablation run. Each set of Sr/Ca data have isotope-specific argon blank values

173

deducted. The values for 88

Sr/43

Ca are noticeably higher than the three other isotopic

ratios due to greater abundance of 88

Sr. In contrast, greater abundance of 44

Ca reduces

the ratio of 86

Sr/44

Ca dramatically.

Figure 6.7 Graphical comparison of different Sr/Ca isotope ratios in enamel

Additionally, Figure 6.8 is an adjusted comparison of the four combinations with

86Sr/

44Ca values multiplied by 5 and

88Sr/

43Ca divided by 10 to produce more comparable

distributions. Notably, all four patterns mimic each other closely, particularly in areas of

significant peaks and valleys. This expected consistency of strontium and calcium ratios

demonstrates the capacity of laser sampling and ICP-MS (semi-) quantification of enamel

composition and confirms the utility of any Sr/Ca isotope ratio in reflecting important

relative information regarding element behavior over development time.

Logarithmic Comparison of Various Sr/Ca Isotope Ratios

0.00

0.01

0.10

1.00

10.00

0 100 200 300 400 500 600 700 800

Reading #

Lo

g S

r/C

a

86Sr/44Ca

88Sr/44Ca

86Sr/43Ca

88Sr/43Ca

174

As expected, other alkaline elements are also comparable, namely 137

Ba, 138

Ba, 24

Mg

and 25

Mg. Between the two elements, Mg parallels Sr and Ca better than Ba, although

25Mg sometimes appears stable when

88Sr and

43Ca increase. Barium generally follows

the other alkaline elements, but also can differ at times.

Figure 6.8 Adjusted comparison of different Sr/Ca isotope ratios

Since results of LA-ICP-MS are in the form of element values per reading number or

counts, in order to assess Sr/Ca change over developmental time, the reading numbers

were converted to relative ages of crown formation. The exact period of enamel

development sampled for each canine is based on the relative lengths of laser ablations

and unablated enamel compared to established models of crown formation time.

Comparison of Various Sr/Ca Isotope Ratios

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0 100 200 300 400 500 600 700 800

Reading #

Sr/

Ca R

ati

o

86Sr/44Ca x 5

88Sr/44Ca

86Sr/43Ca

88Sr/43Ca /10

175

In this study, permanent maxillary canines are attributed to begin enamel

development at around birth and finish at 5.0 years, while permanent mandibular canines

are delayed by 0.5 years (see Appendix A.4). As outlined in Appendix A, approximately

one year of initial crown development is buried in inner enamel of permanent canines

(Reid and Dean 2000), and thus not recognized macroscopically. Determination of the

timing of surface enamel defects accounts for this year of cuspal enamel (Appendix A).

For LA-ICP-MS, however, which samples inner enamel, some buried cuspal enamel

is analyzed. In this case, it is appropriate to assume a shorter period of “hidden” enamel

that is not examined. Only 0.5 years is considered missing from the initial period of

crown development so that the periods of enamel development sampled by laser ablation

in this study are 0.5-5.0 years in maxillary canines and 1.0-5.5 years in mandibular

canines.

However, not all teeth have enamel dating to the first age interval (0.5-0.75 years)

that could be sampled because of cuspal wear and the need to sample non-surface

(potentially contaminated) enamel. No enamel is available from the latest period of

development either, due to the thinness of enamel near the CEJ, but it is represented by

averaged values for the last interval (5.25-5.5 years).

Due to the large number of element readings spanning the period from 0.5-5.5 years,

Sr/Ca values for ablated enamel were reduced to averages for 0.25 year (3 month)

intervals. Three month intervals could be differentiated since reading numbers can easily

be converted to age in years based on the total period of enamel development ablated in

each tooth (see Section 6.7). The 0.25 year interval is the main unit of analysis in this

study. Scatter plot distributions are presented in Chapter Seven.

176

Statistical analyses were undertaken with SPSS (version 11.0) software. Inter- and

intra-comparisons of Sr/Ca values are provided by one-way ANOVA’s with level set at

p>0.05 (two-tailed) (see Appendix C). Comparisons are made at the level of overall

Sr/Ca change; temporal period; age (children vs. adults) and adult sex. Importantly,

temporal comparisons indicate that the total Postclassic and Historical samples differ

significantly at many age intervals. Throughout the entire period of permanent canine

enamel formation, Postclassic mean Sr/Ca is elevated compared to Historical values (see

Section 7.2).

Some distinctions are also noted between Postclassic and Historical adults (Section

7.3). The nature of the difference and the implications for dietary supplementation

timing are illustrated by adjusted scatter plots in Section 7.3. Adjusted graphs are also

presented for comparisons that are not statistically significant, but which might have

implications for delays in attaining Sr/Ca levels in certain cohorts.

177

CHAPTER 7

RESULTS OF ANALYSIS

7.1 Major Findings

The primary focus of this investigation is to assess whether Sr/Ca composition in

sequentially calcified enamel can be observed to reflect changes in infant diet from

exclusive breastfeeding to complete food dependence (weaning). This dietary transition

represents one of the most significant developmental stages in human life.

Ancient Maya teeth are used in this LA-ICP-MS analysis to specifically examine the

nature of infant feeding through the transition from indigenous prehistory to Spanish

colonial history. This historic period offers a dynamic cultural context to the analysis

that can be reflected in the human remains. Age, sex and temporal cohorts are compared

to provide insight into varying dietary practices and differences in infant care.

The results suggest that enamel Sr/Ca does record the process of infant dietary

supplementation, from predominant breast milk intake to predominant solid food

reliance. This is reflected in rising Sr/Ca values from 0.5 to 5.5 years of age, as solid

food supplementation is introduced and augmented over time. The mean Sr/Ca pattern

over time for the entire Lamanai sample is outlined in Section 7.2, which generally

follows the proposed model in Section 5.6. From the data, the weaning process entails an

approximately two-fold increase in enamel Sr/Ca (see Table 7.15).

It should be stressed, however, that hard tissue Sr/Ca can only reliably be used to

identify the introduction and consumption of solid foods among infants. Currently, only

178

nitrogen isotopes can be used to identify the cessation of breast milk intake (weaning) in

hard tissues (see Chapter Five). One can infer that peak Sr/Ca represents the age of

weaning, i.e., maximum solid food intake, but it is complicated by two opposing realities:

1) weaning may have occurred earlier than the age of peak Sr/Ca, which may only reflect

the (later) age of efficient Sr discrimination by mature digestive systems; 2) increased

discrimination of Sr by the gut and reduced Sr/Ca values thereafter does not rule out the

continued intake of some breast milk after attaining peak Sr/Ca. Nevertheless, in this

case, when nursing is extended (i.e., beyond two years), breast milk consumption likely

reflects a minimal (insignificant) dietary contribution (see Section 8.2).

As discussed in Section 6.8, utilization of LA-ICP-MS in this analysis results in the

ratioing of specific isotopes of strontium and calcium, which does not directly compare

with total Sr/Ca data. Nevertheless, comparison of various Sr/Ca isotope patterns in

Chapter Six indicates that 86

Sr/43

Ca provides highly reliable relative information about

the nature of strontium change during enamel development. Total Sr/Ca ratios can be

derived from the specific isotope ratios and are presented in Section 7.2, but the primary

unit of analysis in this investigation is the 86

Sr/43

Ca ratio, which is considerably larger

than total Sr/Ca values. Here, permanent canine enamel 86

Sr/43

Ca ratios vary from 0.014-

0.179, with the majority between 0.02-0.14, while total Sr/Ca values range from 0.199-

2.454 x 10-3

(0.000199-0.002454).

Temporally, the Postclassic and Historical samples differ significantly in average

Sr/Ca values of permanent canine enamel, with Historical individuals displaying lower

Sr/Ca ratios at all age intervals (Figure 7.2). It is suggested that the Historical pattern

reflects a process of food supplementation and weaning that is delayed compared to

179

Postclassic Lamanai Maya. The mean age for peak Sr/Ca is 5 years among Postclassic

individuals and no earlier than 5.25 years, and possibly as late as 6.25 years, in Historical

individuals (see discussion of Figure 7.7).

Section 7.3 describes averaged Sr/Ca data for age, sex and temporal cohorts.

Comparisons are made between time periods for adult males, females and children and

hypotheses provided for differences in mean Sr/Ca values and overall pattern. Most

differences are not statistically significant, but Historical adults consistently exhibit lower

mean Sr/Ca than Postclassic adults at the same age interval. Lower mean Sr/Ca values

are interpreted to reflect a possible delay in acquiring a comparable level of food

supplementation. Shifting Sr/Ca distributions between cohorts demonstrates the potential

consequences of distinctions that are not necessarily statistically significant (see below).

Specific Sr/Ca details for all individuals are tabulated and illustrated graphically in

Section 7.4 according to age, sex and temporal context. Individual graphs demonstrate

the extent of variation in Sr/Ca patterns over development time (Figures 7.15-7.20).

While most individuals display an overall increase in Sr/Ca over time, the total sample

pattern between 0.5 and 5.5 years of age includes many subtle fluctuations, which is

thought to reflect intermittent changes in relative breast milk and solid food intake.

Four patterns can be discerned from the Sr/Ca data: 1) gradual increase in food

supplementation (Sr/Ca) until complete weaning; 2) delay in significant food

supplementation followed by a rapid transition to weaning; 3) fluctuations in relative

breast milk and solid food intake over time; 4) generally stable enamel Sr/Ca over time

(see Section 7.5).

180

Within each pattern, enamel Sr/Ca suggests that there is tremendous variation

between and within individuals. The transition to complete food dependence can be

recognized in rising Sr/Ca values over time, but many children experience alternating

periods of changing relative breast milk and food intake. These fluctuations likely reflect

the interaction of changing socioeconomic conditions (e.g., access to food resources),

maternal health and infant illnesses.

7.2 The Lamanai Sr/Ca Pattern

As postulated in this study, Sr/Ca values increase significantly over time during the

development of secondary canine enamel (0.5-5.5 years of age). Figure 7.1 illustrates

standard error bars for mean 86

Sr/43

Ca values of the entire sample at each age interval,

which are summarized in Table 7.1. Two standard deviations on either side of the mean

are included in each bar.

The greatest variation appears at both extremes of the distribution, where Sr/Ca

values often exhibit significant fluctuations. This is likely due to instrumentation and

sampling factors: for example, the start of enamel sampling after a period of argon gas

blank readings is often marked by a considerable peak in Sr/Ca, and the end of enamel

ablation sampling is also characterized by erratic element readings (see Chapter Six).

Notably, the significant increase visible at 0.75 years of age (9 months) suggests that

most Lamanai infants began food supplementation at around this age. This is followed

by gradual food supplementation, which seems to accelerate after the age of two years

(see further below). Peak Sr/Ca values at 5-5.25 years of age suggest that Lamanai

181

children may not have been completely dependent on solid foods until this late age.

Alternatively, it may reflect the age when digestive systems fully mature and efficiently

discriminate against strontium, which thereafter diminishes in hard tissue concentration.

Figure 7.1 Standard Error graph of mean 86

Sr/43

Ca for all Lamanai individuals

Age in Years

5.5

5 4.5 4 3.5 3 2.5 2 1.5 1 0.5

Mean S

r/C

a +

- 2 S

E

.10

.08

.06

.04

.02

0.00

.12

182

Below, Table 7.1 summarizes the mean 86

Sr/43

Ca ratios for 0.25 year intervals

between 0.5 and 5.5 years of age for Postclassic and Historical cohorts, as well as the

total sample. It is clear that mean Sr/Ca values increase with developmental age.

Graphically, the Postclassic and Historical data from this table are compared in Figure

7.2, which reflects distinctions in mean Sr/Ca at every age interval (see below for

elaboration). Additionally, Figure 7.2 is a standard error graph of the mean Sr/Ca data

for the two cohorts.

Table 7.1 Summary of mean 86

Sr/43

Ca for 0.25 year intervals

Age Interval Postclassic Historical Total Sample

0.50-0.74 0.05914 0.03653 0.04557

0.75-0.99 0.05843 0.04384 0.04968

1.00-1.24 0.05665 0.04661 0.05083

1.25-1.49 0.05674 0.04898 0.05227

1.50-1.74 0.05794 0.04999 0.05344

1.75-1.99 0.06021 0.05145 0.05525

2.00-2.24 0.06296 0.05248 0.05702

2.25-2.49 0.06472 0.05415 0.05873

2.50-2.74 0.06686 0.05579 0.06059

2.75-2.99 0.07034 0.05749 0.06306

3.00-3.24 0.07396 0.05992 0.06600

3.25-3.49 0.07628 0.06143 0.06787

3.50-3.74 0.07782 0.06357 0.06974

3.75-3.99 0.08006 0.06582 0.07199

4.00-4.24 0.08335 0.06810 0.07456

4.25-4.49 0.08542 0.06768 0.07520

4.50-4.74 0.08770 0.06954 0.07724

4.75-4.99 0.08860 0.07025 0.07828

5.00-5.24 0.09563 0.07217 0.08312

5.25-5.49 0.08718 0.07542 0.08154

183

Figure 7.2 Standard Error graph of mean Sr/Ca for Postclassic and

Historical individuals

Analyses of Variance (ANOVA) indicate significant differences between

Analyses of Variance (ANOVA) indicate significant differences between Postclassic

and Historical cohorts only between 2.25 to 4.75 years of age (see Table 7.2). During

this period, the rate of Sr/Ca increase among Postclassic individuals is slightly

accelerated compared to Historical period Maya at Lamanai. It appears that Postclassic

children after 2.25 years of age increase their intake of solid foods relative to breast milk,

while Historical children consume relatively less solid foods, i.e., maintain the same

proportions of food and breast milk intake as earlier.

Age in Years

5.2554.75

4.54.254

3.753.5

3.2532.75

2.52.252

1.751.5

1.2510.75

0.5

Mea

n +

- 2

SE

.12

.10

.08

.06

.04

.02

0.00

Postclassic

Historical

184

Table 7.2 Results of ANOVA comparing Postclassic and Historical individuals

(underlined values indicate significance at p>0.05)

ANOVA

.001 1 .001 4.786 .060

.002 8 .000

.003 9

.001 1 .001 3.023 .095

.010 23 .000

.011 24

.001 1 .001 3.627 .063

.016 48 .000

.018 49

.001 1 .001 2.134 .150

.023 57 .000

.024 58

.001 1 .001 2.203 .143

.024 58 .000

.025 59

.001 1 .001 2.518 .118

.026 58 .000

.027 59

.002 1 .002 3.581 .063

.026 58 .000

.028 59

.002 1 .002 4.026 .049

.024 58 .000

.025 59

.002 1 .002 4.028 .049

.026 58 .000

.028 59

.002 1 .002 4.495 .038

.031 58 .001

.034 59

.003 1 .003 4.877 .031

.034 58 .001

.037 59

.003 1 .003 4.881 .031

.038 58 .001

.042 59

.003 1 .003 4.471 .039

.039 58 .001

.042 59

.003 1 .003 4.276 .043

.040 58 .001

.043 59

.003 1 .003 4.620 .036

.041 57 .001

.045 58

.005 1 .005 6.180 .016

.042 57 .001

.046 58

.005 1 .005 6.062 .017

.045 57 .001

.049 58

.004 1 .004 4.603 .037

.040 46 .001

.044 47

.004 1 .004 4.116 .052

.028 28 .001

.032 29

.001 1 .001 .907 .351

.022 23 .001

.023 24

Between Groups Within Groups Total Between Groups Within Groups Total Between Groups Within Groups Total Between Groups Within Groups Total Between Groups Within Groups Total Between Groups Within Groups Total Between Groups Within Groups Total Between Groups Within Groups Total Between Groups Within Groups Total Between Groups Within Groups Total Between Groups Within Groups Total Between Groups Within Groups Total Between Groups Within Groups Total Between Groups Within Groups Total Between Groups Within Groups Total Between Groups Within Groups Total Between Groups Within Groups Total Between Groups Within Groups Total Between Groups Within Groups Total Between Groups Within Groups Total

0.5

0.75

1

1.25

1.5

1.75

2

2.25

2.5

2.75

3

3.25

3.5

3.75

4

4.25

4.5

4.75

5

5.25

Sum of Squares

df Mean Square F Sig.

185

In light of the significant difference in mean Sr/Ca ratios between Postclassic and

Historical cohorts, it should be noted that the low Historical values are partially

influenced by two individuals (YDL-85/50B and YDL-85/68B) with consistently very

low values throughout enamel development (see Section 7.5 and Figure 7.29). Several

explanations are presented in Section 7.5, but they are excluded from mean values in the

following tables (7.3-7.4) and figures.

First, for the purposes of developmental and nutritional significance and research

comparisons, the mean Sr/Ca data is condensed into fewer age intervals of greater length

(in years) in Table 7.3 below. Number of values (N) refers to the number of averaged

0.25 year intervals in the new age range available from each cohort. (These figures

exclude two Historical individuals (YDL-85/50B and /68B) with very low values.)

Table 7.3 Mean 86

Sr/43

Ca ratios for intervals between 0.5 and 5.5 years of age

Age Interval

Postclassic S.D.

N Historical S.D.

N Total Sample

S.D.

0.5-1.0

0.05863

0.01854

14

0.04610

0.01739

18

0.05158

0.01870

1.0-1.5 0.05670 0.01942 46 0.05006 0.01775 59 0.05297 0.01871

1.5-2.0 0.05907 0.02006 52 0.05287 0.01989 64 0.05565 0.02012

2.0-3.0 0.06622 0.02139 104 0.05731 0.01977 128 0.06131 0.02095

3.0-4.0 0.07703 0.02365 104 0.06543 0.02499 128 0.07063 0.02502

4.0-5.0 0.08617 0.02754 96 0.07189 0.02541 121 0.07821 0.02725

5.0-5.5 0.09156 0.02565 27 0.07356 0.03512 28 0.08240 0.03187

From these data, total Sr/Ca values can be calculated to contextualize this study in the

field of hard tissue strontium research. This is possible by considering the known

abundances of 86

Sr and 43

Ca relative to total strontium and calcium. 86

Sr is 9.86% of the

186

total naturally occurring abundance of strontium, while 43

Ca is 0.135% of total calcium.

With these constants, 86

Sr/43

Ca ratios are converted to total Sr/Ca values in Table 7.4.

The values range from 0.199 - 2.454 x 10-3

(0.000199-0.002454), with mean values

ranging from 0.631 - 1.254 x 10-3

(0.000631-0.001254). These ratios accord well with

other nutritional research: Sillen and Smith (1984) calculated bone Sr/Ca values ranging

from approximately 1.5 x 10-3

(0.0015) to 3.0 x 10-3

(0.003), while Mays (2003) has

reported more comparable bone Sr/Ca ratios in the range of 0.5 x 10-3

(0.0005) to 1.05 x

10-3

(0.00105), or a mean value of 0.855 x 10-3

(0.000855) among juveniles and 0.692 x

10-4

(0.000692) among adults. In particular, Mays’ (2003: Figure 1) mean ratio of

approximately 0.88 x 10-3

for infants less than a year old corresponds well with the total

Lamanai ratio of 0.706 x 10-3

for infants 0.5-1.0 years of age (Table 7.4).

The Sr/Ca ratios fall within the normal range of human enamel variation discussed in

Chapter Four, but there is considerable variation evident, even compared to other

research (Mays 2003; Sillen and Smith 1984). This can be attributed to numerous

factors: differences in food and water intake, and individual variation in strontium

absorption and hard tissue incorporation. Foremost, the continuous method of tissue

sampling in this investigation allows disclosure of much more previously undetected

variation.

Comparatively, the Postclassic sample can be distinguished by mean Sr/Ca values

higher than the total sample mean at all age intervals, while the reverse is true for the

Historical cohort, which is consistently lower than the total sample mean. This is clearly

apparent in Figure 7.3, which illustrates the distribution of mean Sr/Ca ratios for each

cohort presented in Table 7.4.

187

Table 7.4 Mean total Sr/Ca data (x 10-3

) for Postclassic and Historical cohorts

Age Interval (in years)

Postclassic

Range

N Historical

Range

N

Total Sample

0.5-1.0 0.803 0.518-1.263

14

0.631 0.248-1.153

18

0.706

1.0-1.5 0.776 0.346-1.398

46 0.685 0.199-1.267

59 0.725

1.5-2.0 0.809 0.393-1.549

52 0.724 0.214-1.430

64 0.762

2.0-3.0 0.907 0.441-1.653

104 0.785 0.216-1.324

128 0.839

3.0-4.0 1.055 0.595-1.866

104 0.896 0.248-1.728

128 0.967

4.0-5.0 1.180 0.613-2.454

96 0.984 0.450-1.871

121 1.071

5.0-5.5 1.254 0.741-2.047

27 1.007 0.443-2.285

28 1.128

188

Figure 7.3 Scatter plot distributions of total Sr/Ca for Lamanai cohorts

Distribution of Sr/Ca ratios in Historical Lamanai individuals

0.000

0.250

0.500

0.750

1.000

1.250

1.500

1.750

2.000

2.250

2.500

0 0.5-1.0 1.0-1.5 1.5-2.0 2.0-3.0 3.0-4.0 4.0-5.0 5.0-5.5 Age Interval (in years)

Sr/

Ca R

ati

o (

x 1

0-3

)

Distribution of Sr/Ca ratios in Postclassic Lamanai individuals

0.000

0.250

0.500

0.750

1.000

1.250

1.500

1.750

2.000

2.250

2.500

0 0.5-1.0 1.0-1.5 1.5-2.0 2.0-3.0 3.0-4.0 4.0-5.0 5.0-5.5 Age Interval (in years)

Sr/

Ca r

ati

o (

x 1

0-3

)

189

Significantly, like the specific 86

Sr/43

Ca pattern in Figure 7.1, the distribution of mean

total Sr/Ca ratios in Figure 7.3 reflects a pattern of increase and slight stabilization that

supports the hypothesis of this investigation. In fact, after the age of four years, it is

likely that Sr/Ca stabilizes at a greater rate than mean values would suggest; it appears

that mean values after this age are being inflated by several very high Sr/Ca ratios.

As also observed by Haverkort (2001: 183), the non-Gaussian distribution of

elements in teeth is not completely suited to the use of the sample mean as an indicator of

central tendency. Nonetheless, it remains a useful indicator of relative similarities or

distinctions. In this study, where single teeth can amass 800-900 element readings,

averaging counts over 0.25 year intervals for age, sex and temporal cohorts facilitates

data analysis and recognition of inter- and intra-sample variation.

Examining the total Sr/Ca pattern provides meaningful inferences for infant nutrition

of Lamanai Maya as a whole, particularly the significant increase in Sr/Ca at around nine

months that represents the start of food supplementation, but importantly, cohort

comparisons and extensive individual variation can also be observed with LA-ICP-MS.

The variation between and among temporal, age and sex cohorts is explored in the

following sections. Rather than total Sr/Ca, the unit of analysis is the 86

Sr/43

Ca ratio,

since these particular isotopes were directly quantified by LA-ICP-MS in this

investigation. Unless specified, the “Sr/Ca” ratio refers to the comparison of these single

isotopes rather than total Sr/Ca.

190

7.3 The Sr/Ca Patterns of Lamanai Cohorts

The Lamanai sample was evaluated on the basis of age (children vs. adults), sex

(female vs. male) and temporal period (Postclassic vs. Historical). Each category is

presented graphically by averaging Sr/Ca values for each 0.25 year age interval between

0.5 and 5.25-5.5 years. The following graph demonstrates the mean Sr/Ca values for

children, females and males from the Postclassic (N10) and Historical (YDL) periods at

Lamanai.

Figure 7.4 Sr/Ca patterns of Lamanai cohorts

Average Sr/Ca values for 0.25 yr intervals among

Postclassic and Historical Lamanai Individuals

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6

Age in years

Sr/

Ca

ra

tio

N10 Children N10 Females N10 Males YDL Children YDL Females YDL Males

191

As Figure 7.4 illustrates, the mean values for Postclassic and Historical children,

females and males generally mimic each other in terms of rate of Sr/Ca increase and

degree of overall increase. ANOVA’s indicate no significant difference in Sr/Ca between

age or sex cohorts within temporal periods (Tables 7.5-7.8).

Table 7.5 Results of Single Factor ANOVA (two-tailed) comparing

Postclassic Children and Adults (Sr/Ca at 0.25 year intervals)

Postclassic Children and Adults

Groups Count Sum Mean Variance

df F P-value F crit

Kids 0.5 2 0.09034 0.04517 0.00005 3 15.27498 0.05967 18.51276 Ads0.5 2 0.14623 0.07312 0.00005

Kids 0.75 4 0.20988 0.05247 0.00030 9 0.56532 0.47366 5.31764 Ads0.75 6 0.37437 0.06240 0.00049

Kids 1 6 0.29717 0.04953 0.00029 19 1.04811 0.31951 4.41386 Ads1 14 0.83352 0.05954 0.00044

Kids 1.25 6 0.30785 0.05131 0.00037 23 0.49096 0.49085 4.30094 Ads1.25 18 1.04393 0.05800 0.00042

Kids 1.5 6 0.29658 0.04943 0.00026 24 1.25559 0.27405 4.27934 Ads1.5 19 1.14157 0.06008 0.00045

Kids 1.75 6 0.30671 0.05112 0.00028 24 1.40049 0.24873 4.27934 Ads1.75 19 1.18664 0.06245 0.00046

Kids 2 6 0.32747 0.05458 0.00033 24 1.05537 0.31496 4.27934 Ads2 19 1.23218 0.06485 0.00049

Kids 2.25 6 0.34680 0.05780 0.00038 24 0.85259 0.36541 4.27934 Ads2.25 19 1.26389 0.06652 0.00041

Kids 2.5 6 0.34065 0.05677 0.00035 24 1.73462 0.20079 4.27934 Ads2.5 19 1.32519 0.06975 0.00047

Kids 2.75 6 0.37256 0.06209 0.00079 24 0.85462 0.36485 4.27934 Ads2.75 19 1.38193 0.07273 0.00055

Kids 3 6 0.37283 0.06214 0.00048 24 1.75369 0.19842 4.27934 Ads3 19 1.46755 0.07724 0.00062

Kids 3.25 6 0.39215 0.06536 0.00045 24 1.54094 0.22699 4.27934 Ads3.25 19 1.51137 0.07955 0.00064

Kids 3.5 6 0.40421 0.06737 0.00032 24 1.61625 0.21632 4.27934 Ads3.5 19 1.54217 0.08117 0.00060

Kids 3.75 6 0.41496 0.06916 0.00035 24 1.50116 0.23289 4.27934 Ads3.75 19 1.57843 0.08308 0.00065

Kids 4 6 0.43063 0.07177 0.00047 23 1.49751 0.23400 4.30094 Ads4 18 1.57042 0.08725 0.00079

Kids 4.25 6 0.43395 0.07233 0.00042 23 1.55557 0.22543 4.30094 Ads4.25 18 1.61688 0.08983 0.00102

Kids 4.5 6 0.42925 0.07154 0.00044 23 2.76773 0.11036 4.30094 Ads4.5 18 1.67401 0.09300 0.00084

Kids 4.75 4 0.30462 0.07615 0.00055 19 0.85081 0.36852 4.41386 Ads4.75 16 1.45161 0.09073 0.00085

Kids 5 2 0.16001 0.08001 0.00050 12 0.60277 0.45389 4.84434 Ads5 11 1.07150 0.09741 0.00089

Kids 5.25 3 0.25276 0.08425 0.00081 12 0.09161 0.76778 4.84434 Ads5.25 10 0.89269 0.08927 0.00060

192


Postclassic Females and Males (Sr/Ca at 0.25 year intervals)

Postclassic Females and Males

Groups* Count Sum Mean Variance df F P-value F crit

Fem0.75 5 0.33568 0.06714 0.00044 5 1.53018 0.28375 7.70865 Male0.75 1 0.03870 0.03870 N/A

Fem1 9 0.55501 0.06167 0.00048 13 0.24351 0.63059 4.74722 Male1 5 0.27851 0.05570 0.00044

Fem1.25 11 0.68828 0.06257 0.00049 17 1.43833 0.24787 4.49400 Male1.25 7 0.35565 0.05081 0.00028

Fem1.5 12 0.76424 0.06369 0.00052 18 0.92622 0.34934 4.45132 Male1.5 7 0.37733 0.05390 0.00034

Fem1.75 12 0.78660 0.06555 0.00056 18 0.67197 0.42371 4.45132 Male1.75 7 0.40005 0.05715 0.00030

Fem2 12 0.82220 0.06852 0.00055 18 0.88769 0.35930 4.45132 Male2 7 0.40998 0.05857 0.00038

Fem2.25 12 0.83502 0.06959 0.00045 18 0.72750 0.40555 4.45132 Male2.25 7 0.42886 0.06127 0.00037

Fem2.5 12 0.87157 0.07263 0.00055 18 0.56655 0.46193 4.45132 Male2.5 7 0.45361 0.06480 0.00035

Fem2.75 12 0.90650 0.07554 0.00066 18 0.45086 0.51095 4.45132 Male2.75 7 0.47543 0.06792 0.00040

Fem3 12 0.96391 0.08033 0.00079 18 0.48237 0.49673 4.45132 Male3 7 0.50364 0.07195 0.00038

Fem3.25 12 0.98693 0.08224 0.00077 18 0.35894 0.55700 4.45132 Male3.25 7 0.52444 0.07492 0.00045

Fem3.5 12 0.99102 0.08258 0.00077 18 0.10421 0.75077 4.45132 Male3.5 7 0.55116 0.07874 0.00036

Fem3.75 12 0.99497 0.08291 0.00076 18 0.00122 0.97255 4.45132 Male3.75 7 0.58346 0.08335 0.00056

Fem4 11 0.96493 0.08772 0.00105 17 0.00759 0.93165 4.49400 Male4 7 0.60549 0.08650 0.00049

Fem4.25 11 0.99639 0.09058 0.00160 17 0.01481 0.90465 4.49400 Male4.25 7 0.62049 0.08864 0.00023

Fem4.5 11 1.03343 0.09395 0.00110 17 0.02856 0.86793 4.49400 Male4.5 7 0.64057 0.09151 0.00053

Fem4.75 9 0.84098 0.09344 0.00102 15 0.16922 0.68703 4.60011 Male4.75 7 0.61062 0.08723 0.00073

Fem5 6 0.61787 0.10298 0.00078 10 0.43608 0.52556 5.11736 Male5 5 0.45363 0.09073 0.00114

Fem5.25 5 0.47264 0.09453 0.00071 9 0.43560 0.52779 5.31764 Male5.25 5 0.42005 0.08401 0.00056

* ANOVA was not possible at the 0.5 year interval due to insufficient data

(lack of earliest developing canine enamel among Postclassic males)

193


Historical Children and Adults (Sr/Ca at 0.25 year intervals)

Historical Children and Adults

Groups Count Sum Mean Variance df F P-value F crit

Kids 0.5 2 0.08834 0.04417 0.00012 5 0.70560 0.44818 7.70865 Ads0.5 4 0.13081 0.03270 0.00029

Kids 0.75 4 0.15685 0.03921 0.00031 14 0.25278 0.62353 4.66719 Ads0.75 11 0.50077 0.04552 0.00051

Kids 1 9 0.42220 0.04691 0.00023 28 0.00377 0.95148 4.21001 Ads1 20 0.92937 0.04647 0.00036

Kids 1.25 9 0.45277 0.05031 0.00042 33 0.04976 0.82490 4.14909 Ads1.25 25 1.21257 0.04850 0.00044

Kids 1.5 9 0.47784 0.05309 0.00051 33 0.26645 0.60927 4.14909 Ads1.5 25 1.22192 0.04888 0.00042

Kids 1.75 9 0.48534 0.05393 0.00055 33 0.15423 0.69713 4.14909 Ads1.75 25 1.26390 0.05056 0.00047

Kids 2 9 0.48725 0.05414 0.00047 33 0.07166 0.79066 4.14909 Ads2 25 1.29715 0.05189 0.00047

Kids 2.25 9 0.49945 0.05549 0.00037 33 0.05010 0.82432 4.14909 Ads2.25 25 1.34172 0.05367 0.00046

Kids 2.5 9 0.51406 0.05712 0.00043 33 0.04641 0.83079 4.14909 Ads2.5 25 1.38267 0.05531 0.00048

Kids 2.75 9 0.52248 0.05805 0.00049 33 0.00741 0.93195 4.14909 Ads2.75 25 1.43209 0.05728 0.00054

Kids 3 9 0.52691 0.05855 0.00051 33 0.03772 0.84722 4.14909 Ads3 25 1.51049 0.06042 0.00065

Kids 3.25 9 0.54858 0.06095 0.00052 33 0.00381 0.95118 4.14909 Ads3.25 25 1.54020 0.06161 0.00082

Kids 3.5 9 0.58571 0.06508 0.00060 33 0.03528 0.85219 4.14909 Ads3.5 25 1.57552 0.06302 0.00086

Kids 3.75 9 0.62978 0.06998 0.00068 33 0.26277 0.61175 4.14909 Ads3.75 25 1.60799 0.06432 0.00085

Kids 4 9 0.67403 0.07489 0.00080 33 0.76154 0.38935 4.14909 Ads4 25 1.64150 0.06566 0.00072

Kids 4.25 9 0.67580 0.07509 0.00078 33 1.05428 0.31222 4.14909 Ads4.25 25 1.62540 0.06502 0.00059

Kids 4.5 9 0.69170 0.07686 0.00087 33 0.82536 0.37041 4.14909 Ads4.5 25 1.67280 0.06691 0.00077

Kids 4.75 9 0.69766 0.07752 0.00078 26 0.74953 0.39486 4.24170 Ads4.75 18 1.19914 0.06662 0.00103

Kids 5 5 0.39210 0.07842 0.00023 15 0.22539 0.64229 4.60011 Ads5 11 0.76260 0.06933 0.00167

Kids 5.25 4 0.31256 0.07814 0.00031 11 0.02911 0.86793 4.96459 Ads5.25 8 0.59250 0.07406 0.00204

194


Historical Females and Males (Sr/Ca at 0.25 year intervals)

Historical Females and Males

Groups* Count Sum Mean Variance df F P-value F crit

Fem0.75 6 0.20677 0.03446 0.00024 10 4.18371 0.07114 5.11736

Male0.75 5 0.29401 0.05880 0.00057

Fem1 8 0.34199 0.04275 0.00043 19 0.49835 0.48926 4.41386 Male1 12 0.58739 0.04895 0.00033

Fem1.25 13 0.58623 0.04509 0.00049 24 0.71174 0.40756 4.27934 Male1.25 12 0.62634 0.05220 0.00039

Fem1.5 13 0.58174 0.04475 0.00045 24 1.10439 0.30422 4.27934 Male1.5 12 0.64018 0.05335 0.00039

Fem1.75 13 0.60493 0.04653 0.00053 24 0.93576 0.34343 4.27934 Male1.75 12 0.65897 0.05491 0.00040

Fem2 13 0.64215 0.04940 0.00061 24 0.34790 0.56105 4.27934 Male2 12 0.65500 0.05458 0.00035

Fem2.25 13 0.64362 0.04951 0.00055 24 1.01163 0.32498 4.27934 Male2.25 12 0.69810 0.05818 0.00036

Fem2.5 13 0.67428 0.05187 0.00055 24 0.65850 0.42541 4.27934 Male2.5 12 0.70839 0.05903 0.00041

Fem2.75 13 0.70098 0.05392 0.00061 24 0.55458 0.46400 4.27934 Male2.75 12 0.73111 0.06093 0.00049

Fem3 13 0.74855 0.05758 0.00083 24 0.32557 0.57381 4.27934 Male3 12 0.76193 0.06349 0.00050

Fem3.25 13 0.77394 0.05953 0.00111 24 0.13688 0.71478 4.27934 Male3.25 12 0.76626 0.06386 0.00057

Fem3.5 13 0.78107 0.06008 0.00120 24 0.26361 0.61255 4.27934 Male3.5 12 0.79445 0.06620 0.00055

Fem3.75 13 0.82460 0.06343 0.00127 24 0.02418 0.87777 4.27934 Male3.75 12 0.78339 0.06528 0.00046

Fem4 13 0.84387 0.06491 0.00114 24 0.02013 0.88840 4.27934 Male4 12 0.79763 0.06647 0.00033

Fem4.25 13 0.81894 0.06300 0.00088 24 0.18078 0.67465 4.27934 Male4.25 12 0.80646 0.06721 0.00031

Fem4.5 13 0.83177 0.06398 0.00109 24 0.29363 0.59311 4.27934 Male4.5 12 0.84103 0.07009 0.00047

Fem4.75 10 0.68550 0.06855 0.00134 17 0.07696 0.78501 4.49400 Male4.75 8 0.51364 0.06421 0.00077

Fem5 6 0.44710 0.07452 0.00219 10 0.19533 0.66895 5.11736 Male5 5 0.31550 0.06310 0.00135

Fem5.25 5 0.36461 0.07292 0.00186 7 0.00728 0.93477 5.98737 Male5.25 3 0.22789 0.07596 0.00341

* ANOVA was not possible at the 0.5 year interval due to insufficient data

(lack of earliest developing canine enamel among Historical males)

195

Lack of significant difference in the mean Sr/Ca ratios of Lamanai children, females

and males within temporal period reflects a general weaning pattern shared among

Lamanai infants in the Postclassic and Historical periods. According to enamel Sr/Ca,

this weaning process is long and protracted, lasting as much as five years.

Specifically, within temporal periods, Sr/Ca patterns exhibit comparable rates of

increase and degree of overall increase. This is not unexpected as the composition of

Postclassic and Historical samples is generally uniform in socioeconomic status and

burial context. Figures 7.5a and 7.5b display the mean Sr/Ca patterns of children, adult

females and males for the Postclassic and Historical periods.

Comparing individuals by time period reflects a slight difference in the feeding

experiences of Lamanai infants before and after Spanish contact. In the Postclassic graph

(Figure 7.5a), the average Sr/Ca values for children seem to parallel the rate of increase

among females, but progresses at a slower rate compared to adult males (whose slope is

steeper).

Though not significantly, Postclassic juvenile Sr/Ca values are clearly lower than

male and female adults (Figure 7.5a). If Sr/Ca ratio is indicative of relative solid food

intake, as proposed in this study, then this suggests that those who died in childhood were

slightly delayed in the supplementation of food compared to those who survived to

adulthood (also see Figure 7.8).

Early supplementation (i.e., prior to six postnatal months) has been widely linked to

increased morbidity and mortality (see Chapter Five), but these results also indicate that

delayed supplementation later in infancy, when toddlers experience rapid growth and

development, also has negative consequences. Extended reliance on breast milk and

196

Figure 7.5 Average Sr/Ca for Postclassic and Historical individuals

a)

b)

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6

Sr/

Ca r

ati

o

Age in years

Average Sr/Ca values for 0.25 yr intervals among Postclassic individuals

N10 Children

N10 Females

N10 Males

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6

Sr/

Ca r

ati

o

Age in years

Average Sr/Ca values for 0.25 yr intervals among Historical individuals

YDL Children

YDL Females

YDL Males

197

accompanied malnutrition due to inadequate food and nutritional supplementation in

these children may account for their premature mortality.

In contrast, Historical groups are strikingly similar in both Sr/Ca ratios and rate of

increase. (The slight difference being that Sr/Ca increase speeds up between the ages of

3.25 and 4 years in Historical children [Figure 7.5b].) The effect of colonization seems to

be an “homogenizing” of childhood nutritional experiences.

Furthermore, all Historical groups are slightly diminished (though not significantly)

in mean Sr/Ca compared to Postclassic adults. In Figure 7.6, the total Historical sample

is compared to Postclassic males and females. This graph clearly indicates that the rate

of food supplementation increase among Historical individuals is generally stable

throughout the entire weaning process.

Figure 7.6 Comparison of total Historical sample with Postclassic adults

All Historical vs. Postclassic Adults

(average Sr/Ca for 0.25 yr intervals)

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6

Age in years

Sr/

Ca

ra

tio

N10 Females

N10 M ales

All YDL

198

However, Postclassic males display a steeper Sr/Ca pattern, or accelerated rate of

solid food supplementation, after approximately two years of age. Prior to one year of

age, their Sr/Ca values are the lowest, suggesting a higher proportion of breast milk

intake compared to Postclassic females and Historical individuals. Postclassic females

and the Historical sample share a similar rate of Sr/Ca change, but higher Sr/Ca values

among Postclassic females suggest that they were supplemented with solid foods earlier

than Historical individuals, as well as Postclassic males.

Figure 7.6 suggests that all Historical individuals, including those who lived past

childhood, were delayed in reaching similar levels of food supplementation compared to

Postclassic individuals who survived to adulthood. The similarity among Historical

individuals may reflect a nutritional adaptation to the changing socio-economic

conditions of colonial Lamanai, i.e., access to food resources and/or disease prevalence.

In addition to re-settlement, all Lamanai Maya were “reduced” to a collective,

subordinate, social position in colonial times that might have affected their ability to

supplement infants with food, particularly those afflicted with illness.

In this study, it is proposed that the extent of differences between cohorts can be

interpreted by adjusting the graphical distributions of mean Sr/Ca. Rates of Sr/Ca change

(slope) and total increase are generally comparable between groups (see Figures 7.2 and

7.4), so it is postulated that “shifting” the graphs can reflect tangible differences in the

infant feeding patterns of different cohorts.

Two sets of Sr/Ca data are compared in this way, i.e., Postclassic vs. Historical

individuals, adults vs. children, males vs. females (see Figures 7.7-7.14). Based on

analogous rates of change and overall increase, it is assumed that differences in mean

199

Sr/Ca reflect a time delay in one group reaching comparable Sr/Ca values as the other.

Between two groups, the greater Sr/Ca pattern is horizontally shifted forward in

development time (to the right) to “synchronize” with the lower Sr/Ca pattern (see

Figures 7.7-7.14). The extent required to equalize mean Sr/Ca values reflects the

possible delay in time of the lower Sr/Ca group reaching comparable levels of Sr/Ca, or

food supplementation, as the higher Sr/Ca group. This approach provides a visual

indication of the potential differences between cohorts that may, or may not, be

statistically significant (e.g., Figures 7.7-7.14).

Comparing Lamanai Maya in this way indicates that Historical individuals may have

been delayed by up to 1.25 years in reaching comparable levels of Sr/Ca as Postclassic

individuals (Figure 7.7). An adjustment of 1.25 years results in two distributions that are

generally equal in Sr/Ca values, as well as rate of change (although a small discrepancy

occurs in Historical Sr/Ca after 4 years of age, when Sr/Ca values diminish slightly).

While mean Sr/Ca peaks at 5-5.25 years of age among Postclassic Maya, Historical Maya

may not have reached peak Sr/Ca until 6.25-6.5 years of age. This delay is considered a

maximum difference between samples and assumes that mean Sr/Ca values exhibit

minimal variation, which is known not to be the case (see Chapter Four).

200

Figure 7.7 Comparison of Postclassic and Historical cohorts

a)

b) Time shifted by 1.25 years

Adjusted Postclassic and Historical Lamanai Individuals


0.00

0.02

0.04

0.06

0.08

0.10

0.12

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6

Age in years

Sr/

Ca

ra

tio

Postclassic

Historical

Comparison of all Postclassic and Historical Individuals


0.00

0.02

0.04

0.06

0.08

0.10

0.12

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6

Age in years

Sr/

Ca r

ati

o

Postclassic

Historical

201

Beyond gross temporal comparisons, the Lamanai sample was also compared by

cohorts based on age and sex. In many cases, ANOVA’s indicate lack of statistical

difference (Appendix C). However, some slight discrepancies still exist between

Lamanai groups. As stated earlier, “shifting” the distribution of two sets of data to

“synchronize” mean Sr/Ca values can provide an indication of the extent of time

differences in reaching comparable levels of Sr/Ca, or food supplementation.

Figures 7.8-7.14 illustrate comparative Sr/Ca distributions of Postclassic children vs.

adults; Postclassic males vs. females; Historical children vs. adults; Historical males vs.

females; Postclassic vs. Historical children; Postclassic vs. Historical females and

Postclassic vs. Historical males. They are accompanied by “adjusted” graphs reflecting

the possible time delay in the lower Sr/Ca group. To reiterate, the higher Sr/Ca pattern is

shifted to the right to match up with the lower Sr/Ca values, but the extent of the

adjustment (in years) reflects the delay of the lower group.

In Figure 7.8, teeth from individuals who died in childhood are compared to deceased

adults to ascertain the effects of nutritional status on relative lifespan. Diet, weaning age,

infectious disease and socio-economic factors are clearly associated with rates of

morbidity and mortality in archaeological and living populations (Cook 1981; Goodman

and Armelagos 1988, 1989; Herring et al. 1998; Katzenberg et al. 1996; Stuart-Macadam

and Dettwyler 1995; Swedlund and Ball 1998, among many others). Individuals who

died in childhood are particularly burdened in life with ill health, as reflected in hard

tissue pathologies such as enamel hypoplasia, Wilson bands and porotic hyperostosis

(Blakey and Armelagos 1985; Cook and Buikstra 1979; Goodman and Armelagos 1988,

202

Figure 7.8 Comparison of Postclassic Children and Adults

a)


Postclassic Children vs. Adults


0.00

0.02

0.04

0.06

0.08

0.10

0.12

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6

Age in years

Sr/

Ca r

ati

o

N10 Children N10 Adults

Adjusted Postclassic

Children and Adults

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6

Age in years

Sr/

Ca r

ati

o

N10 Children N10 Adults

203

1989; Huhne-Osterloh and Grupe 1989; Katzenberg et al. 1996; Song 1997; Stuart-

Macadam 1985; Wright 1990).

Figure 7.8a reflects the differences in average Sr/Ca ratio between Postclassic

children and adults, with children averaging lower values at every age interval. While

not statistically significant for any age interval (see Appendix C), Figure 7.8b is an

adjusted scatter plot that demonstrates the possible “delay” in children’s Sr/Ca compared

to adults.

Since Sr/Ca patterns in both cohorts mimic each other in the rate of increase,

adjusting the graphs can reflect a quantifiable difference in the infant feeding patterns of

individuals who died in childhood versus adulthood. In order to synchronize the Sr/Ca

patterns between the two groups, the adult pattern is staggered to begin later in

development age, but in fact, the graph illustrates an approximately 1.5 year “delay”

among Postclassic individuals who died in childhood (in obtaining a comparable level of

solid food supplementation of Postclassic individuals who survived to adulthood).

In comparing Postclassic adults (Figure 7.9), there is no significant difference in

Sr/Ca values at any age interval (Appendix C). Graphically, Postclassic males appear

slightly “delayed”, which is reflected in Figure 7.9b, as well as Figure 7.6.

Synchronizing the two graphs indicates that Postclassic males may have only been

supplemented with comparable levels of solid food 0.25-0.5 years after Postclassic

females. A slightly steeper rate of increase (accelerated food supplementation) in males

may compensate for the delay.

204

Figure 7.9 Comparison of Postclassic Females and Males

a)


Postclassic Females vs. Males


0.00

0.02

0.04

0.06

0.08

0.10

0.12

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6

Age in years

Sr/

Ca r

ati

o

N10 FemalesN10 Males

Adjusted Postclassic Adults

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6

Age in years

Sr/

Ca r

ati

o

N10 FemalesN10 Males

205

If one assumes that male children were preferentially treated compared to females, as

archaeological, ethnohistorical and bone chemical evidence suggest greater adult male

social status in Maya society, e.g., increased access to meat and seafood (White 1986,

1999; White et al. 1993), then the Sr/Ca data reflects such increased investment of

maternal care on male infants. In many patriarchal societies, e.g., Canada, Sweden,

Ireland, France, Guatemala, Ecuador, Brazil, Peru, Taiwan, India, Jordan, Liberia and

Botswana, infant boys have been observed to nurse longer than females (see Fildes 1986;

McKee 1984). Delayed food supplementation in infancy, i.e., after six months of age,

when children require increased nutrients to sustain energy and growth demands, has

potentially negative consequences and is discussed further in Chapter Eight.

In terms of socioeconomic status, the Postclassic sample as a whole can be

characterized as an advantaged group (Pendergast 1981; White 1986). Two adult male

individuals are particularly recognized elites: N10-2/20 and N10-4/46A. But while N10-

4/46A exhibits a generally increasing Sr/Ca pattern over time, values for N10-2/20 do not

significantly start to increase until 2.5 years of age (see Figure 7.17), which suggests a

delay period much longer than the 0.25-0.5 year period suggested above. (Remember,

though, that this individual does not have enamel sampled from before one year of age,

when Sr/Ca [food supplementation] might have already started to rise).

206

Figure 7.10 Comparison of Historical Children and Adults

As stated earlier, and presented graphically above, all Historical individuals likely

shared a common pattern of breast milk consumption and delayed food supplementation

compared to Postclassic individuals. ANOVA’s indicate no significant difference in

Sr/Ca at any age interval (Appendix C).

Figure 7.11 illustrates the mean Sr/Ca patterns of Historical adults. There is no

statistical difference in Sr/Ca patterns between males and females (Appendix C).

Adjusting the scatter plots, however, suggests that Historical females may be delayed in

reaching similar levels of food supplementation (Sr/Ca) by approximately one year

compared to males (Figure 7.11b). This contrasts the prehistoric pattern, when it is the

males who show slight delays in reaching comparable Sr/Ca levels.

Historical Children vs. Adults


0.00

0.02

0.04

0.06

0.08

0.10

0.12

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6

Age in years

Sr/

Ca r

ati

o

YDL ChildrenYDL Adults

207

Figure 7.11 Comparison of Historical Females and Males

a)

b) Time shifted by 1.0 year

Historical Females vs. Males


0.00

0.02

0.04

0.06

0.08

0.10

0.12

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6

Age in years

Sr/

Ca r

ati

o

YDL FemalesYDL Males

Adjusted Historical Adults

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6

Age in years

Sr/

Ca r

ati

o

YDL FemalesYDL Males

208

Figure 7.12 Comparison of Postclassic and Historical Children

Despite differing social conditions, Sr/Ca patterns suggest that Postclassic and

Historical Lamanai infants who died in later childhood shared similar patterns of infant

nutrition, with no statistical difference in Sr/Ca over time (Figure 7.12). As it has been

shown above that both Postclassic and Historical children are “delayed” compared to

Postclassic adults (who also exhibit higher Sr/Ca values than Historical adults), the

parallel graphs of Lamanai individuals who died in childhood reflect a pattern of Sr/Ca

increase and food supplementation that is likely sub-optimal for development and, in the

long term, detrimental to survival.

Postclassic vs. Historical Children


0.00

0.02

0.04

0.06

0.08

0.10

0.12

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6

Age in years

Sr/

Ca r

ati

o

N10 Children

YDL Children

209

Figure 7.13 Comparison of Postclassic and Historical Females

a)


Postclassic vs. Historical Females


0.00

0.02

0.04

0.06

0.08

0.10

0.12

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6

Age in years

Sr/

Ca r

ati

o

N10 FemalesYDL Females

Adjusted Females

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6

Age in years

Sr/

Ca r

ati

o

N10 FemalesYDL Females

210

The comparisons between Postclassic and Historical females show the greatest

number of differences in Sr/Ca, with N10 females having higher Sr/Ca ratios at every age

interval. Specifically, ANOVA’s highlight significance at the following age intervals:

0.50-0.749 (p=0.037); 0.75-0.99 (p=0.016); 1.50-1.749 (p=0.042); 2.25-2.49 (0.035);

2.50-2.749 (0.037); 2.75-2.99 (0.043); and 4.50-4.749 (0.038) (Appendix C: Table C.13).

In the adjusted graph (Figure 7.13b), Historical women seem to be delayed by as much as

2.25 years in reaching comparable Sr/Ca levels as Postclassic women. This suggests that

Postclassic females were supplemented with relatively more weanling foods than

Historical female infants of the same age and likely began the weaning process earlier as

well.

Postclassic and Historical males start off with comparable Sr/Ca values and rate of

increase, but noticeably differ after the age of two (Figure 7.14). After 2-2.25 years,

Postclassic males consume supplementary foods at an accelerated rate compared to

Historical males, whose rate of supplementation continues increasing at the same rate

prior to 2 years of age. This acceleration of solid food intake after 2 years of age (most

likely comprising the predominant food source) is also apparent in graphs for Lamanai

individuals with a pattern of “steady increase” in Sr/Ca (see Figures 7.22 and 7.23).

Figure 7.14b suggests that after 2.25 years of age, Historical males are “delayed” in

reaching comparable Postclassic Sr/Ca values by approximately 1.5 years. In total,

Historical male toddlers were relying on more breast milk / less solid food intake than

their prehistoric counterparts. Statistically, however, Postclassic and Historical males

only differ in average Sr/Ca at the 4.0-4.249 age interval (p=0.047) and 4.25-4.49 age

interval (p=0.016) (Appendix C: Table C.14).

211

Figure 7.14 Comparison of Postclassic and Historical Males

a)

b) Time shifted by 1.5 years after the age of 2.25

Postclassic vs. Historical Males


0.00

0.02

0.04

0.06

0.08

0.10

0.12

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6

Age in years

Sr/

Ca r

ati

o

N10 Males

YDL Males

Adjusted Males

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6

Age in years

Sr/

Ca r

ati

o

N10 Males

YDL Males

212

7.4 Sr/Ca Patterns among Lamanai Individuals

The following tables display average Sr/Ca values for 0.25 year intervals among

Postclassic and Historical period children, females and males. Age intervals are in years

and represent a 0.25 year period (3 months). Blank values in each table indicate areas in

which enamel is either missing, or could not be ablated due to poor preservation.

Underlined values represent the highest Sr/Ca reading for each individual. Values for

“Greatest Increase” are based on the highest mean Sr/Ca interval and the first mean Sr/Ca

reading for the individual. In some cases, when the lowest value is not the first (earliest)

Sr/Ca reading, but rather, is the second interval reading, then this value is used to derive

the degree of “greatest increase”. Accompanying the tables are scatter plots of the mean

Sr/Ca values for each age interval among Postclassic and Historical children, females and

males (Figures 7.15-7.20).

213

Table 7.9 Average Sr/Ca values for 0.25 year intervals of Postclassic Children

Age Interval

N10-2/16

N10-2/21

N10-2/44

N10-2/49

N10-2/50

N10-4/2A

AVERAGE

S.D.

N

RANGE

0.50-0.74 - 0.040 0.050 - - - 0.045 0.007 2 0.040 - 0.050

0.75-0.99 - 0.039 0.058 - 0.038 0.075 0.052 0.017 4 0.038 - 0.075

1.00-1.24 0.052 0.043 0.059 0.025 0.042 0.076 0.050 0.017 6 0.025 - 0.076

1.25-1.49 0.058 0.042 0.056 0.027 0.041 0.083 0.051 0.019 6 0.027 - 0.083

1.50-1.74 0.055 0.041 0.053 0.029 0.043 0.076 0.049 0.016 6 0.029 - 0.076

1.75-1.99 0.057 0.043 0.053 0.031 0.043 0.080 0.051 0.017 6 0.031 - 0.080

2.00-2.24 0.060 0.044 0.066 0.032 0.044 0.083 0.055 0.018 6 0.032 - 0.083

2.25-2.49 0.062 0.043 0.073 0.035 0.047 0.086 0.058 0.019 6 0.035 - 0.086

2.50-2.74 0.064 0.044 0.052 0.041 0.049 0.092 0.057 0.019 6 0.041 - 0.092

2.75-2.99 0.064 0.046 0.051 0.045 0.048 0.118 0.062 0.028 6 0.045 - 0.118

3.00-3.24 0.065 0.054 0.051 0.047 0.052 0.105 0.062 0.022 6 0.047 - 0.105

3.25-3.49 0.071 0.056 0.048 0.051 0.061 0.105 0.065 0.021 6 0.048 - 0.105

3.50-3.74 0.078 0.057 0.048 0.059 0.064 0.098 0.067 0.018 6 0.048 - 0.098

3.75-3.99 0.082 0.057 0.045 0.065 0.068 0.098 0.069 0.019 6 0.045 - 0.098

4.00-4.24 0.091 0.059 0.045 0.064 0.068 0.104 0.072 0.022 6 0.045 - 0.104

4.25-4.49 0.085 0.061 0.045 0.065 0.075 0.103 0.072 0.020 6 0.045 - 0.103

4.50-4.74 0.085 0.058 0.051 0.057 0.073 0.106 0.072 0.021 6 0.051 - 0.106

4.75-4.99 0.095 - 0.056 0.056 - 0.098 0.076 0.023 4 0.056 - 0.098

5.00-5.24 0.096 - - 0.064 - - 0.080 0.022 2 0.064 - 0.096

5.25-5.49 0.088 - - 0.054 - - 0.071 0.024 2 0.054 - 0.088

Greatest increase

1.830

1.522

1.442

2.569

1.990

1.576

1.821

0.420

Figure 7.15 Graph of Sr/Ca change among Postclassic children

Sr/Ca change among Postclassic Lamanai children

(3 month intervals)

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

0.16

0.18

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6

Age in Years

Sr/

Ca R

ati

o

N10-2/16

N10-2/21

N10-2/44

N10-2/49

N10-2/50

N10-4/2A

214

Table 7.10 Average Sr/Ca values for 0.25 year intervals of Postclassic Females

Age Interval

N10-2/4 N10-4/1 N10-4/2B

N10-4/4 N10-4/10 N10-4/11 N10-4/19 N10-4/33 N10-4/40 N10-4/45 N10-4/46b N10-4/46c AVERAGE S.D. N RANGE

0.50-0.74 - - - - - - - 0.078 - - 0.068 - 0.073 0.007 2 0.068 - 0.078

0.75-0.99 - 0.085 - - 0.043 0.053 - 0.092 - - 0.063 - 0.067 0.021 5 0.043 - 0.092

1.00-1.24 - 0.086 0.076 - 0.042 0.046 0.036 0.093 - 0.037 0.064 0.075 0.062 0.022 9 0.036 - 0.093

1.25-1.49 - 0.090 0.070 0.048 0.039 0.046 0.039 0.102 0.078 0.039 0.062 0.074 0.064 0.023 10 0.039 - 0.102

1.50-1.74 0.045 0.102 0.074 0.050 0.041 0.048 0.041 0.102 0.080 0.041 0.068 0.073 0.065 0.023 11 0.041 - 0.102

1.75-1.99 0.045 0.113 0.082 0.050 0.044 0.050 0.044 0.094 0.085 0.042 0.067 0.071 0.067 0.024 11 0.042 - 0.113

2.00-2.24 0.048 0.110 0.090 0.057 0.046 0.045 0.046 0.092 0.090 0.044 0.074 0.079 0.070 0.024 11 0.044 - 0.110

2.25-2.49 0.052 0.101 0.092 0.057 0.049 0.047 0.053 0.084 0.093 0.046 0.073 0.090 0.071 0.022 11 0.046 - 0.101

2.50-2.74 0.060 0.116 0.102 0.056 0.048 0.051 0.053 0.094 0.091 0.049 0.073 0.078 0.074 0.024 11 0.048 - 0.116

2.75-2.99 0.067 0.121 0.113 0.054 0.050 0.051 0.055 0.100 0.096 0.052 0.068 0.081 0.077 0.026 11 0.050 - 0.121

3.00-3.24 0.072 0.119 0.132 0.061 0.050 0.056 0.057 0.109 0.100 0.055 0.069 0.084 0.082 0.029 11 0.050 - 0.132

3.25-3.49 0.073 0.126 0.136 0.071 0.051 0.056 0.062 0.105 0.094 0.056 0.074 0.083 0.083 0.029 11 0.051 - 0.136

3.50-3.74 0.074 0.117 0.135 0.064 0.052 0.058 0.061 0.113 0.102 0.055 0.074 0.085 0.084 0.029 11 0.052 - 0.135

3.75-3.99 0.073 0.117 0.133 0.073 0.051 0.056 0.060 0.110 0.110 0.058 0.071 0.084 0.084 0.029 11 0.051 - 0.133

4.00-4.24 0.077 0.111 0.149 0.079 0.052 0.056 0.065 0.126 0.112 0.053 - 0.085 0.089 0.034 10 0.052 - 0.149

4.25-4.49 0.076 0.100 0.179 0.075 0.055 0.053 0.070 0.135 0.118 0.049 - 0.086 0.092 0.042 10 0.049 - 0.179

4.50-4.74 0.085 0.105 0.152 0.087 0.060 0.059 0.073 0.130 0.131 0.050 - 0.101 0.095 0.035 10 0.050 - 0.152

4.75-4.99 0.096 - 0.131 0.062 0.058 0.068 0.120 0.131 0.059 - 0.115 0.093 0.032 9 0.058 - 0.131

5.00-5.24 0.116 - 0.134 - - 0.079 - 0.123 0.061 - 0.105 0.103 0.028 6 0.061 - 0.134

5.25-5.49 0.111 - 0.118 - - - - 0.110 0.056 - 0.078 0.095 0.027 5 0.056 - 0.118

Greatest increase

2.589

1.480

2.363

1.800

1.438

1.115

2.163

1.734

1.677

1.653

1.084

1.536

1.719

0.459

215

Table 7.11 Average Sr/Ca values for 0.25 year intervals of Postclassic Males

Age Interval

N10-2/5 N10-2/20 N10-2/22 N10-2/40 N10-2/42 N10-4/43 N10-4/46A AVERAGE S.D. N RANGE

0.50-0.74 - - - - - - - - - 0 - -

0.75-0.99 - - - 0.039 - - - 0.039 n/a 1 0.039 -

1.00-1.24 0.092 0.046 - 0.041 0.043 - 0.055 0.056 0.021 5 0.041 - 0.092

1.25-1.49 0.085 0.044 0.033 0.042 0.045 0.049 0.058 0.051 0.017 7 0.033 - 0.085

1.50-1.74 0.091 0.046 0.032 0.047 0.046 0.055 0.061 0.054 0.019 7 0.032 - 0.091

1.75-1.99 0.090 0.048 0.035 0.049 0.055 0.059 0.063 0.057 0.017 7 0.035 - 0.090

2.00-2.24 0.095 0.048 0.033 0.050 0.052 0.066 0.066 0.059 0.020 7 0.033 - 0.095

2.25-2.49 0.095 0.050 0.033 0.057 0.057 0.071 0.066 0.061 0.019 7 0.033 - 0.095

2.50-2.74 0.097 0.056 0.036 0.059 0.064 0.076 0.066 0.065 0.019 7 0.036 - 0.097

2.75-2.99 0.103 0.060 0.037 0.064 0.068 0.077 0.066 0.068 0.020 7 0.037 - 0.103

3.00-3.24 0.109 0.070 0.043 0.068 0.069 0.079 0.065 0.072 0.020 7 0.043 - 0.109

3.25-3.49 0.118 0.071 0.050 0.070 0.068 0.082 0.064 0.075 0.021 7 0.050 - 0.118

3.50-3.74 0.119 0.073 0.061 0.079 0.069 0.082 0.069 0.079 0.019 7 0.061 - 0.119

3.75-3.99 0.131 0.080 0.064 0.083 0.064 0.092 0.069 0.083 0.024 7 0.064 - 0.131

4.00-4.24 0.130 0.078 0.069 0.085 0.072 0.101 0.071 0.086 0.022 7 0.069 - 0.130

4.25-4.49 0.119 0.082 0.077 0.079 0.085 0.099 0.079 0.089 0.015 7 0.077 - 0.119

4.50-4.74 0.140 0.087 0.075 0.088 0.074 0.099 0.078 0.092 0.023 7 0.074 - 0.140

4.75-4.99 0.143 0.086 0.065 0.078 0.061 0.093 0.084 0.087 0.027 7 0.061 - 0.143

5.00-5.24 0.149 0.085 0.068 - 0.068 - 0.083 0.091 0.034 5 0.068 - 0.149

5.25-5.49 0.126 0.080 0.071 - 0.069 - 0.075 0.084 0.024 5 0.069 - 0.126

Greatest increase

1.624

1.874

2.334

2.263

1.957

2.038

1.519

1.944

0.303

216

Figure 7.16 Graph of Sr/Ca change among Postclassic females

Figure 7.17 Graph of Sr/Ca change among Postclassic males

Sr/Ca change among Postclassic Lamanai males

(3 month intervals)

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

0.16

0.18

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6

Age in Years

Sr/

Ca R

ati

o

N10-2/5

N10-2/20

N10-2/22

N10-2/40

N10-2/42

N10-4/43

N10-4/46A

Sr/Ca change among Postclassic Lamanai females

(3 month intervals)

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

0.16

0.18

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6

Age in Years

Sr/

Ca R

ati

o

N10-2/4 N10-4/1 N10-4/2B N10-4/10 N10-4/11 N10-4/19 N10-4/33 N10-4/40 N10-4/45 N10-4/46b N10-4/46c

217

Table 7.12 Average Sr/Ca values for 0.25 year intervals of Historical Children

Age Interval

YDL 85/44

YDL 85/54

YDL 85/59

YDL 85/63

YDL 85/65

YDL 85/68B

YDL 85/71A

YDL 85/80

YDL 85/91A

AVERAGE

S.D.

N

RANGE

0.50-0.74 0.052 0.036 - - - - - - - 0.044 0.011 2 0.036 - 0.052

0.75-0.99 0.056 0.038 - - 0.047 0.015 - - - 0.039 0.018 4 0.015 - 0.056

1.00-1.24 0.061 0.040 0.038 0.049 0.045 0.016 0.054 0.052 0.068 0.047 0.015 9 0.016 - 0.068

1.25-1.49 0.062 0.039 0.038 0.048 0.048 0.017 0.055 0.053 0.093 0.050 0.021 9 0.017 - 0.093

1.50-1.74 0.062 0.043 0.039 0.059 0.048 0.017 0.059 0.051 0.100 0.053 0.023 9 0.017 - 0.100

1.75-1.99 0.060 0.045 0.041 0.060 0.045 0.017 0.061 0.052 0.104 0.054 0.023 9 0.017 - 0.104

2.00-2.24 0.064 0.044 0.041 0.058 0.046 0.017 0.063 0.059 0.097 0.054 0.022 9 0.017 - 0.097

2.25-2.49 0.065 0.047 0.043 0.061 0.048 0.017 0.063 0.071 0.084 0.055 0.019 9 0.017 - 0.084

2.50-2.74 0.068 0.042 0.042 0.068 0.049 0.018 0.068 0.078 0.081 0.057 0.021 9 0.018 - 0.081

2.75-2.99 0.068 0.043 0.041 0.076 0.048 0.017 0.068 0.072 0.089 0.058 0.022 9 0.017 - 0.089

3.00-3.24 0.070 0.043 0.043 0.067 0.047 0.017 0.073 0.074 0.092 0.059 0.023 9 0.017 - 0.092

3.25-3.49 0.077 0.044 0.043 0.067 0.054 0.018 0.082 0.076 0.087 0.061 0.023 9 0.018 - 0.087

3.50-3.74 0.081 0.048 0.044 0.076 0.060 0.018 0.079 0.088 0.092 0.065 0.024 9 0.018 - 0.092

3.75-3.99 0.104 0.057 0.047 0.075 0.068 0.019 0.084 0.082 0.094 0.070 0.026 9 0.019 - 0.104

4.00-4.24 0.107 0.060 0.050 0.074 0.072 0.019 0.096 0.096 0.099 0.075 0.028 9 0.019 - 0.107

4.25-4.49 0.123 0.065 0.057 0.080 0.072 0.020 0.089 0.079 0.089 0.075 0.028 9 0.020 - 0.123

4.50-4.74 0.134 0.063 0.061 0.072 0.073 0.024 0.091 0.090 0.084 0.077 0.029 9 0.024 - 0.134

4.75-4.99 0.133 0.068 0.063 0.075 0.067 0.029 0.091 0.094 0.079 0.078 0.028 9 0.029 - 0.133

5.00-5.24 - - 0.062 0.068 - - 0.082 0.102 0.079 0.078 0.015 5 0.062 - 0.102

5.25-5.49 - - 0.060 - - 0.081 0.102 0.070 0.078 0.018 4 0.060 - 0.102

Greatest increase

2.568

1.871

1.678

1.610

1.548

1.887

1.782

1.951

1.532

1.825

0.317

Figure 7.18 Graph of Sr/Ca change among Historical children

Sr/Ca change among Historical Lamanai children

(3 month intervals)

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

0.16

0.18

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6

Age in Years

Sr/

Ca r

ati

o

YDL 85/44

YDL 85/54

YDL 85/59

YDL 85/63

YDL 85/65

YDL 85/68B

YDL 85/71A

YDL 85/80

YDL 85/91A

218

Table 7.13 Average Sr/Ca values for 0.25 year intervals of Historical Females

Age Interval

YDL 85-17

YDL 85-21

YDL 85-23

YDL 85-27

YDL 85-31

YDL 85-41

YDL 85-46

YDL 85-50B

YDL 85-53

YDL 85-62

YDL 85-78C

YDL 85-101

YDL 85-102

AVERAGE

S.D.

N

RANGE

0.50-0.74 0.050 0.018 - - - - 0.045 0.018 - - - - - 0.033 0.017 4 0.018 - 0.050

0.75-0.99 0.054 0.020 - - - - 0.046 0.014 - 0.039 - 0.033 - 0.034 0.016 6 0.014 - 0.054

1.00-1.24 0.065 0.020 - - - 0.043 0.048 0.015 0.075 0.045 - 0.031 - 0.043 0.021 8 0.015 - 0.075

1.25-1.49 0.056 0.022 0.015 0.072 0.076 0.043 0.050 0.016 0.081 0.048 0.034 0.029 0.043 0.045 0.022 13 0.015 - 0.081

1.50-1.74 0.065 0.022 0.016 0.062 0.074 0.044 0.051 0.016 0.079 0.047 0.030 0.031 0.045 0.045 0.021 13 0.016 - 0.079

1.75-1.99 0.060 0.024 0.018 0.070 0.074 0.046 0.045 0.016 0.093 0.046 0.029 0.035 0.050 0.047 0.023 13 0.016 - 0.093

2.00-2.24 0.071 0.025 0.018 0.078 0.078 0.047 0.047 0.018 0.094 0.048 0.031 0.036 0.051 0.049 0.025 13 0.018 - 0.094

2.25-2.49 0.073 0.027 0.016 0.075 0.081 0.045 0.050 0.018 0.085 0.052 0.030 0.037 0.055 0.050 0.024 13 0.016 - 0.085

2.50-2.74 0.081 0.036 0.016 0.076 0.085 0.046 0.052 0.017 0.076 0.060 0.031 0.039 0.059 0.052 0.024 13 0.016 - 0.085

2.75-2.99 0.093 0.035 0.017 0.074 0.093 0.049 0.056 0.019 0.071 0.057 0.032 0.044 0.061 0.054 0.025 13 0.017 - 0.093

3.00-3.24 0.099 0.035 0.018 0.085 0.110 0.053 0.057 0.019 0.069 0.048 0.035 0.048 0.074 0.058 0.029 13 0.018 - 0.110

3.25-3.49 0.107 0.035 0.019 0.082 0.113 0.053 0.056 0.019 0.049 0.039 0.035 0.057 0.111 0.060 0.033 13 0.019 - 0.113

3.50-3.74 0.117 0.035 0.022 0.076 0.111 0.055 0.062 0.020 0.044 0.034 0.035 0.055 0.115 0.060 0.035 13 0.020 - 0.117

3.75-3.99 0.126 0.038 0.032 0.078 0.122 0.060 0.059 0.020 0.046 0.035 0.040 0.056 0.113 0.063 0.036 13 0.020 - 0.126

4.00-4.24 0.117 0.043 0.051 0.067 0.119 0.058 0.060 0.021 0.051 0.038 0.034 0.062 0.123 0.065 0.034 13 0.021 - 0.123

4.25-4.49 0.116 0.047 0.058 0.069 0.120 0.056 0.057 0.021 0.054 0.033 0.034 0.067 0.087 0.063 0.030 13 0.021 - 0.120

4.50-4.74 0.132 0.056 0.060 0.070 0.131 0.052 0.063 0.022 0.049 0.035 0.037 0.067 0.058 0.064 0.033 13 0.022 - 0.132

4.75-4.99 0.137 0.055 0.055 0.069 0.129 - 0.073 0.022 0.047 - 0.042 - 0.056 0.069 0.037 10 0.022 - 0.137

5.00-5.24 - - 0.065 0.071 0.167 - - - 0.050 - 0.036 - 0.059 0.075 0.047 6 0.036 - 0.167

5.25-5.49 - - 0.059 0.073 0.146 - - - 0.052 - 0.034 - - 0.073 0.043 5 0.034 - 0.146

Greatest increase

2.758

3.065

4.447

1.179

2.188

1.383

1.604

1.247

1.260

1.514

1.224

2.007

2.849

2.056

0.982

219

Table 7.14 Average Sr/Ca values for 0.25 year intervals of Historical Males

Age Interval

YDL I-68

YDL 85/32

YDL 85/33

YDL 85/35

YDL 85/47

YDL 85/73

YDL 85/78A

YDL 85/86

YDL 85/87B

YDL 85/97

YDL 85/98

YDL 85/98

AVERAGE

S.D.

N

RANGE

0.50-0.74 - - - - - - - - - - - - - - 0 - -

0.75-0.99 0.063 0.035 - - - - - 0.078 0.033 0.084 - - 0.059 0.024 5 0.033 - 0.084

1.00-1.24 0.062 0.037 0.026 0.026 0.049 0.046 0.051 0.079 0.033 0.080 0.058 0.042 0.049 0.018 12 0.026 - 0.080

1.25-1.49 0.071 0.038 0.032 0.026 0.055 0.046 0.051 0.082 0.033 0.088 0.059 0.046 0.052 0.020 12 0.026 - 0.088

1.50-1.74 0.070 0.041 0.031 0.027 0.058 0.048 0.055 0.083 0.032 0.088 0.060 0.048 0.053 0.020 12 0.027 - 0.088

1.75-1.99 0.072 0.042 0.031 0.027 0.058 0.054 0.059 0.085 0.035 0.089 0.060 0.048 0.055 0.020 12 0.027 - 0.089

2.00-2.24 0.074 0.043 0.029 0.028 0.059 0.051 0.057 0.081 0.038 0.082 0.065 0.048 0.055 0.019 12 0.028 - 0.082

2.25-2.49 0.073 0.043 0.032 0.031 0.059 0.057 0.064 0.089 0.047 0.089 0.062 0.052 0.058 0.019 12 0.031 - 0.089

2.50-2.74 0.077 0.042 0.031 0.034 0.053 0.051 0.068 0.090 0.045 0.093 0.062 0.062 0.059 0.020 12 0.031 - 0.093

2.75-2.99 0.083 0.045 0.032 0.036 0.053 0.054 0.073 0.095 0.038 0.094 0.065 0.066 0.061 0.022 12 0.032 - 0.095

3.00-3.24 0.090 0.050 0.032 0.043 0.053 0.057 0.073 0.094 0.037 0.099 0.061 0.074 0.063 0.022 12 0.032 - 0.099

3.25-3.49 0.089 0.052 0.040 0.042 0.049 0.051 0.075 0.107 0.034 0.094 0.054 0.079 0.064 0.024 12 0.034 - 0.107

3.50-3.74 0.094 0.056 0.046 0.044 0.052 0.049 0.084 0.103 0.038 0.098 0.053 0.077 0.066 0.023 12 0.038 - 0.103

3.75-3.99 0.098 0.054 0.049 0.041 0.051 0.049 0.084 0.104 0.050 0.086 0.054 0.064 0.065 0.022 12 0.041 - 0.104

4.00-4.24 0.099 0.056 0.053 0.041 0.059 0.048 0.093 0.082 0.065 0.078 0.056 0.067 0.066 0.018 12 0.041 - 0.099

4.25-4.49 0.097 0.059 0.052 0.046 0.052 0.053 0.094 0.077 0.066 0.084 0.052 0.074 0.067 0.018 12 0.046 - 0.097

4.50-4.74 0.104 0.058 0.060 0.045 0.057 0.040 0.097 0.090 0.064 0.094 0.053 0.079 0.070 0.022 12 0.040 - 0.104

4.75-4.99 0.112 - 0.058 0.048 0.055 0.036 0.103 - 0.055 - 0.046 - 0.064 0.028 8 0.036 - 0.112

5.00-5.24 - - 0.053 0.049 0.055 0.032 0.127 - - - - - 0.063 0.037 5 0.032 - 0.127

5.25-5.49 - - - 0.050 - 0.035 0.143 - - - - - 0.076 0.058 3 0.035 - 0.143

Greatest increase

1.762

1.689

2.316

1.965

1.209

1.241

2.828

1.363

2.004

1.173

1.126

1.872

1.712

0.524

220

Figure 7.19 Graph of Sr/Ca change among Historical females

Figure 7.20 Graph of Sr/Ca change among Historical males

Sr/Ca change among Historical Lamanai females

(3 month intervals)

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

0.16

0.18

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6

Age in Years

Sr/

Ca R

ati

o YDL 85-17

YDL 85-21

YDL 85-23

YDL 85-27

YDL 85-31

YDL 85-41

YDL 85-46

YDL 85-50B

YDL 85-53

YDL 85-62

YDL 85-78C

YDL 85-101

YDL 85-102

Sr/Ca change among Historical Lamanai males

(3 month intervals)

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

0.16

0.18

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6

Age in Years

Sr/

Ca R

ati

o

YDL I-68

YDL 85/32

YDL 85/33

YDL 85/35

YDL 85/47

YDL 85/73

YDL 85/78A

YDL 85/86

YDL 85/87B

YDL 85/97

YDL 85/98

YDL 85/98

221

As the tables indicate, Sr/Ca change over developmental time in Lamanai individuals

involves a roughly twofold increase in values. Table 7.15 lists the average Sr/Ca increase

for Postclassic and Historical cohorts.

Table 7.15 Average greatest increase in Sr/Ca from infancy to early childhood

(0.5-5.5 yrs) among Postclassic and Historical period individuals

Average S.D. N

Postclassic Children

1.821

0.420

6

Females 1.719 0.459 12

Males 1.944 0.303 7

Combined1

1.807 0.399 261

Historical Children 1.825 0.317 9

Females 2.056 0.982 13

Males 1.712 0.524 12

Combined 1.873 0.700 34

1 Average greatest increase for Combined Postclassic individuals includes one adult of

indeterminate sex (N10-4/44) who is not included in the Postclassic male or female means

One-way Analyses of Variance (ANOVA) with level set at p>0.05 indicate no

significant difference in Sr/Ca increase between Postclassic children and adults (p=0.922)

and between Postclassic females and males (p=0.266) (Appendix C: Table C.1-C.2).

This is also the case between Historical children and adults (p=0.813) and Historical

males and females (p=0.292). Temporal comparisons between cohorts also indicate no

statistical distinction in Sr/Ca increase over developmental time (see Appendix C.1).

Historical females have a slightly higher average rise (2.056) due to two individuals

with noticeably greater Sr/Ca increases: YDL-85/21 (3.065) and YDL-85/23 (4.447).

Removing them from the sample reduces the Historical female average to 1.747

(S.D.=0.616), which is more comparable to the other groups. The inflated increases in

222

these two women may reflect one of several circumstances: individual variation

(reflecting true dietary increase); diagenetically altered enamel, or instrumentation

variables.

The data in Tables 7.9-7.14 also contain important information regarding the ages of

peak Sr/Ca per individual (underlined values). In this case, one can infer that the highest

Sr/Ca values represent the point when maximum solid food intake is attained. Figure

7.21 is a histogram detailing the frequency of peak Sr/Ca values according to 0.25 year

age intervals. In individuals with the same maximum values at different age intervals, the

earliest period is considered to be the age of attaining peak Sr/Ca.

Figure 7.21 Distribution of peak Sr/Ca values per age interval

It is evident from the bar graph that the majority of Lamanai children did not achieve

maximum enamel Sr/Ca ratios until after the age of four years, with many in the range of

4.25 to 5.25 years. Prior to four years of age, 23.1% (6 of 26) of Postclassic individuals

Comparison of Peak Sr/Ca Age

0

1

2

3

4

5

6

7

8

1.75 2 2.25 2.5 2.75 3 3.25 3.5 3.75 4 4.25 4.5 4.75 5 5.25

Age Interval

Nu

mb

er

of

Ind

ivid

uals

Postclassic

Historical

15.4% Postclassic

29.4% Historical

223

and 38.2% (13 of 34) of Historical individuals exhibit peak Sr/Ca values, while after four

years of age, 77.9% (20 of 26) of Postclassic and 61.8% (21 of 34) of Historical

individuals display peak enamel Sr/Ca values.

For the most part, Postclassic and Historical children resemble each other in the

distribution of peak Sr/Ca, but the Historical sample can also be distinguished by more

children attaining maximum Sr/Ca at earlier ages (1.75-3.5 years). Unlike the Postclassic

sample, the Historical cohort assumes a slightly bimodal distribution in the timing of

peak Sr/Ca values (Figure 7.21). If one assumes that peak values represent the age of

maximum solid food intake, then it appears that more Historical children were weaned at

earlier ages than Postclassic individuals. Between 1.75 and 3.5 years of age, Historical

individuals are distinguished for having almost twice the incidence of peak Sr/Ca values:

29.4% of the Historical sample (10 of 34 individuals), while only 15.4% of Postclassic

individuals (4 of 26) exhibit peak values at these earlier ages.

The peak Sr/Ca distribution reflects a Postclassic dietary pattern that is much more

uniform compared to the Historical period. In the Postclassic, maximum Sr/Ca values

infer that most children were completely weaned by 4.25 to 5.25 years of age. Relatively

stable socio-political-economic conditions, and greater socioeconomic status of the entire

Postclassic sample, may account for a weaning pattern that is more conventional in terms

of continued increase in food supplementation over time.

While many Historical children were also weaned at such late ages, the Historical

sample is also noteworthy for many individuals with peak Sr/Ca ratios between 1.75-3.5

years of age. This earlier weaning age might be expected in the Historical period due to

socio-economic, political and biological upheaval, as well as the presumed demands on

adult women for tribute products.

224

Remember though, that while rising Sr/Ca values can reflect the introduction of solid

foods, weaning age can only roughly be inferred by (maximum) hard tissue Sr/Ca values.

Importantly, this presumption is complicated by two opposing realities: 1) weaning may

have occurred earlier than the age of peak Sr/Ca, but Sr/Ca continued to rise due to

inefficient Sr discrimination (thus, peak Sr/Ca may only reflect the age of efficient Sr

discrimination by mature digestive systems); 2) increased discrimination of Sr by the gut

and reduced Sr/Ca values thereafter does not rule out the continued intake of some breast

milk after attaining peak Sr/Ca (see below).

7.5 The Nature of Enamel Sr/Ca Change in Lamanai Individuals

Plotting of Sr/Ca values in Lamanai canines produces graphs generally indicating

positive unidirectional change (Figures 7.22-7.27). Initial enamel development (0.5-1.0

year) is characterized by Sr/Ca values mostly in the range of 0.02-0.08, while the

majority of values at the end of canine crown formation (5-5.5 years) range from 0.04-

0.12. (These ranges reflect the tremendous variation in Sr found in hard tissues [see

Section 4.4]). While mostly increasing over time, Sr/Ca change in Lamanai canines can

be grouped into four patterns: 1) general increase; 2) fluctuating changes; 3) delayed

increase (i.e., period of stability followed by a rise); and 4) general stability.

Figures 7.22-7.27 and 7.29 illustrate such patterns in Postclassic and Historical

Lamanai. Of note, Sr/Ca values plotted at each 0.25 year age (x-axis) reflect average

values for the subsequent interval (e.g., Sr/Ca value at 0.5 years = average for the period

0.50-0.749 years; Sr/Ca value at 5.25 years = average for the period 5.25-5.49 years).

225

Figure 7.22 Graph illustrating Postclassic individuals with a general increase in Sr/Ca over time

Postclassic Individuals with Increasing Sr/Ca over time

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

0.16

0.18

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6

Age in years

Sr/

Ca r

atio

N10-2/4 N10-2/5 N10-2/16 N10-2/40

N10-2/49 N10-4/4N10-4/10 N10-4/19 N10-4/40 N10-4/43

N10-4/44 N10-4/45 N10-4/46A

50% of

Postclassic

sample

226

Figure 7.23 Graph illustrating Historical individuals with a general increase in Sr/Ca over time

Historical Individuals with Increasing Sr/Ca over time

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

0.16

0.18

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6

Age in years

Sr/

Ca r

atio

YDL I-68

YDL 85-17

YDL 85-21

YDL 85-31

YDL 85/32

YDL 85-46 YDL 85/63

YDL 85/71A

YDL 85/78A

YDL 85/80

YDL 85-101

32% of

Historical

sample

227

Generally Increasing Sr/Ca

As postulated in this study, enamel Sr/Ca significantly increases during the period of

permanent canine enamel formation. Figures 7.22 and 7.23 clearly illustrate an

approximately twofold increase between the ages of 0.5 and 5.5 years in 13 Postclassic

(50% of sample) and 11 Historical individuals (32.35% of sample). The degree of overall

Sr/Ca increase is not statistically significant between all Postclassic and Historical

individuals (p= 0.668).

Though not consistently, many individuals do display the pattern of Sr/Ca change

predicted in Chapter Five (Figure 5.1), albeit without the initial period of very low,

stable, Sr/Ca when young infants are exclusively breastfeeding (since enamel from

between 0-0.5 years of age is not available) (see Figures 7.22, 7.23, 7.26, 7.27). Since it

is likely that infants were supplemented with food as early as 6 months of age, due to

inadequate breast milk nutrients, it is not surprising to find Sr/Ca values rising from the

start of canine enamel sampled in this study (0.5-0.75 years).

In most of these individuals, it appears that weanling foods were consumed in a

steady, gradual, manner after their introduction. (Some individuals exhibit Sr/Ca values

that fluctuate slightly, but their overall trend is to increase over time.) After 2-2.5 years

of age, however, the rate of solid food supplementation seems to escalate, most likely to

accommodate increased growth and development (see Figures 7.22-23). Combined with

the declining nutritional quality of breast milk, it is likely that after two years of age,

most Lamanai children were consuming solid foods for the bulk of their energy and

protein requirements, with breast milk comprising a minor nutritional component.

228

As illustrated in Figure 7.22, Sr/Ca values of Postclassic individuals reach their peak

and stabilize between the ages of 3.75-5, or predominantly between 4.5-5 years of age.

After nine months to one year of age, or the period of exclusive/predominant breast milk

intake, the time it takes to reach peak Sr/Ca values ranges from 2.75 (N10-2/49) to 4 years

(N10-2/5) (see Figure 7.22). Notably, Individual N10-4/46A, who is identified as possibly

the last pre-Hispanic ruler of Lamanai (Pendergast 1991b), exhibits an enamel Sr/Ca

pattern that resembles the model of gradual increase in food supplementation over time,

peaking at 4.75 years of age (see Figure 7.22). Assuming that erratic enamel Sr/Ca change

over time reflects extended periods of poor health or nutrition (see below), his strontium

pattern indicates that greater social status might have shielded him from such stressors.

Importantly, it suggests that even children of Maya elites nursed extensively in ancient

times.

Among Historical individuals, Sr/Ca reaches its peak at 3.5-5.25 years of age, or a

period ranging from 3 (YDL-85/71A) to 4.25 years (YDL-85/17) (see Figure 7.23).

Overall, Sr/Ca reaches its peak between 4.5-5 years in most Lamanai individuals. In each

graph, a subsequent drop in Sr/Ca reflects the more efficient discrimination of Sr by

mature digestive systems (see Chapter Four).

229

Fluctuating Sr/Ca

Individuals with fluctuating Sr/Ca over time demonstrate the variable nature of Sr/Ca

in terms of environmental availability, strontium discrimination by the gut, hard tissue

incorporation and solid food intake. Eight of 26 Postclassic (30.77%) and 13 of 34

Historical (38.24%) individuals display variable changes in Sr/Ca between the age of 0.5

and 5.5 years. As noted above, additional individuals listed as having “generally

increasing” Sr/Ca over time can also be described as “fluctuating” in Sr/Ca.

The fluctuations likely reflect true variations in Sr/Ca associated with disruptions or

variations in weanling diet, in addition to changing Sr discrimination and hard tissue

incorporation.

On one hand, shifts in the direction of Sr/Ca over time can be interpreted to reflect

alternating periods of high and low solid food intake, with levels of breastfeeding

dependent on such consumption. To effect such compositional changes, these episodes

are assumed to be several weeks or months in duration, according to the period of Sr/Ca

change evident across enamel (and developmental age). Varying the relative proportion

of breast milk and solid food consumption (as opposed to a positive trajectory of

increased solid food intake) reflects the tenuous nature of the transition from nursing to

solid food dependence. As stated elsewhere, this can be determined by child preference,

illness (maternal and infant), food availability, and the socioeconomic obligations of the

mother.

230

Figure 7.24 Graph illustrating Postclassic individuals with fluctuations in Sr/Ca over time

Postclassic Individuals with Fluctuating Change in Sr/Ca

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

0.16

0.18

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6

Age in years

Sr/

Ca r

atio

N10-2/42

N10-2/44

N10-4/1

N10-4/2A

N10-4/2B

N10-4/33

N10-4/46b

N10-4/46c

31% of

Postclassic

sample

231

Figure 7.25 Graph illustrating Historical individuals with fluctuations in Sr/Ca over time

Historical Individuals with Fluctuating Sr/Ca over time

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

0.16

0.18

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6

Age in years

Sr/

Ca r

atio YDL 85-27

YDL 85/47

YDL 85-53

YDL 85-62

YDL 85/73

YDL 85-78C

YDL 85/86

YDL 85/87B

YDL 85/91A

YDL 85/97

YDL 85/98

YDL 85-102

YDL 85/103

38% of

Historical

sample

232

Alternatively, changing Sr/Ca ratios may reflect variations in the supplementary diet

prior to weaning. Changes in infant solid foods (of differing Sr/Ca abundance) may be

due to seasonal availability of resources, crop failure and other ecological factors, as well

as withholding of taboo foods, or treatment with therapeutic foods/herbs, during illness.

While not recognized ethnographically, possible alternative weanling foods include

mashed immature (not dry) maize (high in Sr/Ca), meat (low in Sr/Ca), and various raw

fruit, nuts or vegetables (high in Sr/Ca).

Beyond dietary availability, a significant factor affecting food intake and the relative

levels of Sr/Ca in these individuals is childhood disease. Gastrointestinal conditions,

which were particularly common in Historical times (White 1986; White et al. 1994),

would have particularly affected an infant’s ability and desire to eat solid foods. Cultural

taboos about diet (e.g., food “contamination”) during illness may also determine feeding

patterns at such times (see Stuart-Macadam and Dettwyler 1995).

Related to this, obviously, is the role of maternal health in infant nutrition. The

ability of mothers to breastfeed and/or properly supplement infants can be severely

compromised by their ill health and/or malnutrition. For both mothers and infants,

periods of illness and poor nutrition that could impact enamel Sr/Ca probably lasted

longer than several weeks, i.e., months. Historical period women and their children

would have been particularly affected by the poor epidemiological conditions of

colonialism. The slightly elevated rate of Historical individuals with fluctuating Sr/Ca

patterns (38.2% compared to 30.8% of Postclassic individuals) is thought to reflect this.

Thus, examining enamel Sr/Ca patterns can provide potential indicators of individual

illness history.

233

In the Lamanai population, among Postclassic adults with fluctuating Sr/Ca, it is

mostly females who display irregular patterns compared to males, who generally exhibit

the expected pattern of increasing Sr/Ca over time (see Figures 7.16 and 7.17). This

suggests that female children may have been more prone to dietary inconsistency than

boys, i.e., shifts in breast milk intake and food supplementation during times of economic

uncertainty or childhood illness. Dietary stability and nutritional advantages among

Lamanai males is also suggested above in comparing the averaged Sr/Ca values for

Postclassic males and females (see Section 7.3).

During the Postclassic period, when Maya elites maintained socioeconomic

dominance over the Lamanai population (Pendergast 1986, 1991a, 1992), gender

differences were more pronounced than in Spanish colonial times, when all Maya were

reduced to a shared, subordinate, position. The Postclassic sample examined in this

analysis is advantaged socio-economically, as a whole, but gender distinctions prevail. It

is, therefore, not surprising that Postclassic males and females display distinctions that

are manifest in hard tissue composition (reflecting varied health and nutrition).

On the other hand, in the Historical period, fluctuating Sr/Ca patterns appear in

comparable frequency among both males and females (see Figures 7.19 and 7.20). This

“equality” in Historical times may reflect the shared predicament of “reduced” Maya

interred in the Lamanai cemetery, and it is also demonstrated in the total mean Sr/Ca

values for Historical males and females (see Section 7.3).

Fluctuating Sr/Ca patterns may also reflect the varied origins of Maya refugees from

the Yucatan and elsewhere. As children, they may have experienced famine, infectious

disease, maternal death and dietary instability related to the demographic upheaval of the

234

colonial period (see Chapter Two).

Among “fluctuating” cases, several Postclassic and Historical individuals show peak

Sr/Ca values comparable to the late ages among “generally increasing” individuals. Four

Postclassic individuals and three Historical individuals have peak values at 4-4.75 years

of age. Many individuals in this category also exhibit patterns indicating that they may

have completed weaning much earlier. These include individuals with peak Sr/Ca values

in the mid-range of the graphs, i.e. 1.75-3.5 years of age (Figures 7.24-25). Three

Postclassic individuals and ten Historical individuals reach maximum Sr/Ca values in this

age range (also see Figure 7.21 for a peak Sr/Ca distribution of the entire sample).

Fluctuations, and in some cases, progressive decline in Sr/Ca after peak values may

reflect developmental variations in Sr discrimination (i.e., increased efficiency), hard

tissue incorporation, changes in weanling diet (e.g., meat, fruits and vegetables) or,

alternatively, subsequent reductions in food intake and resumption of nursing at

intermittent periods. In this instance, peak Sr/Ca values do not necessarily represent the

age at which children were fully dependent on solid foods.

As stated earlier, the association of maximum Sr/Ca ratios with total solid food

reliance is complicated by other factors that can change relative Sr/Ca values. Due to the

immaturity of infant digestive systems, it is possible that if weaning occurred early in

infancy (i.e., first year of life), Sr/Ca might continue to rise due to inefficient

discrimination. However, clinical data appears to refute this after the first year of life,

when Sr discrimination increases, and particularly after the second year, when Sr

absorption is less than one third of the newborn level (more than three times reduced)

(Rivera and Harley 1965). Data by Rivera and Harley (1965) on the Observed Ratio, or

235

physiological discrimination, of strontium indicates that the greatest absorption of Sr

occurs between birth and one year of age, when the OR is approximately 1.00. At one

year of age, this value drops to 0.60, reflecting greater discrimination of Sr, followed by

0.24 at 2 years of age (see Sillen and Smith 1984: Table 1; and Table 7.16 below). By

approximately 9 years of age, the OR reduces to 0.18, which continues to be the average

level of Sr discrimination throughout adulthood (Rivera and Harley 1965).

In fairness, the extent of strontium change at a more micro level is not fully

understood. Even at two, three and four years of age, Rivera and Harley observed some

fluctuations in the observed ratio: 0.24 at two years, 0.25 at three years and 0.24 at four

years of age, followed by a gradual reduction thereafter. In this study, laser ablation

microsampling may be capturing a much greater level of Sr absorption fluctuation, or,

even possibly, compositional inconsistencies at the enamel prism (or prism layer) level.

Related to factors of ill health and poor nutrition, fluctuations in enamel Sr/Ca might

be associated with macroscopic developmental defects of enamel such as hypoplasia and

hypocalcification. However, with enamel hypoplasias, which are deficiencies in the

amelogenesis (enamel matrix formation) stage, periods of Sr/Ca fluctuation do not

necessarily coincide with either the position or presence of defects in teeth, though 62.5%

of hypoplastic Postclassic teeth (5 out of 8) reflect fluctuating Sr/Ca (compared to 46.2%

of hypoplastic Historical teeth [6 out of 13]). Likewise, canines with hypocalcifications,

or disruptions in enamel mineralization (which are more appropriately associated with

element data quantified by ICP-MS) are not likely to exhibit fluctuating Sr/Ca patterns.

In this case, 1 out of 8 (12.5%) hypocalcified Postclassic teeth and 2 out of 13 (15.4%)

Historical teeth have enamel Sr/Ca patterns that fluctuate over time.

236

In total, it appears that hard tissue incorporation of strontium is much more complex

than simply associating enamel composition with dietary intake. The findings can only

suggest that Lamanai infants commonly experienced fluctuations in: 1) the relative intake

of solid foods versus breast milk, and/or the types of weanling foods; 2) Sr discrimination

by the digestive system; or, at least, 3) hard tissue Sr incorporation.

Delayed Increase in Sr/Ca

As illustrated in Figures 7.26 and 7.27, “delayed” individuals are those with initial

Sr/Ca values that appear generally stable for some time prior to increasing. The period of

highest Sr/Ca ratio remains consistent, however, generally peaking between four and five

years of age. The “delayed” pattern closely follows the predicted behavior of strontium

postulated in Chapter Five (Figure 5.1), but in this case, one cannot assume that the initial

low values represent an extended period of exclusive breastfeeding. Insufficient breast

milk nutrients for infants after six months of age implies that the initial low Sr/Ca values

represent an extended period of combined breast milk/low solid food intake. Quantifying

the exact proportion of breast milk and solid food intake in these individuals is beyond

the scope of this study, but relative to other patterns, one could state that these individuals

were consuming considerably less solid food for much longer than other Lamanai infants.

Four Postclassic individuals (2 children, 2 adults; or 15.38% of sample) and nine

Historical individuals (5 children, 4 adults; or 26.47% of sample) are characterized by a

delayed Sr/Ca increase. Thus, almost twice as many Historical individuals exhibit a

delayed Sr/Ca pattern compared to Postclassic individuals. Beyond poor epidemiological

237

Figure 7.26 Graph illustrating Postclassic individuals with a delayed increase in Sr/Ca over time

15% of

Postclassic

sample

Postclassic Individuals with Delayed Sr/Ca Increase over time

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

0.16

0.18

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6

Age in years

Sr/

Ca r

atio

N10-2/20

N10-2/21

N10-2/22

N10-2/50

15% of

Postclassic

sample

238

Figure 7.27 Graph illustrating Historical individuals with a delayed increase in Sr/Ca over time

27% of

Historical

sample

Historical Individuals with Delayed Sr/Ca Increase over time

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

0.16

0.18

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6

Age in years

Sr/

Ca r

atio

YDL 85-23

YDL 85/33 YDL 85/35

YDL 85-41

YDL 85/44 YDL 85/54

YDL 85/59

YDL 85/65YDL 85/68B

27% of

Historical

sample

239

conditions and widespread famine in the early colonial period, this discrepancy may be

related to historical changes at Lamanai regarding women’s roles (see Chapter Eight).

Notably, sex is not a factor in the likelihood of a delayed increase. Social status also

does not exclude the likelihood of delayed Sr/Ca increase: Individual N10-2/20, an elite

male adult, clearly exhibits a delayed pattern (Figure 7.26). However, it should be noted

that as this individual, as well as N10-2/22, are “missing” ablated enamel prior to 1.0 and

1.25 years of age, it is possible that they experienced an earlier increase in Sr/Ca (food

supplementation increase) that is not recognized here and may belong in the “generally

increasing” Sr/Ca category. Strontium data for early enamel development is also absent

for several Historical individuals (Figure 7.27), and should be considered.

Importantly, if it is the case that these “delayed” individuals actually experienced an

earlier rise in Sr/Ca that is not captured in the LA-ICP-MS data, then such patterns

suggest a different model of Sr/Ca behavior in young children. In this case, Sr/Ca

undergoes two phases of positive growth (food supplementation increase), alternating

between two phases of stability: the first reflecting an extended period of consistent food

intake relative to breast milk and the second phase reflecting total reliance on solid food.

Nevertheless, while interesting to consider, the patterns illustrated above do not seem

to indicate an earlier rise in Sr/Ca that might have been excluded from the analysis unless

enamel development times are incorrect. For instance, underestimating the sampling of

buried cuspal enamel might attribute earlier development times to “older” enamel.

(Additional analysis of permanent first molars, to sample enamel from birth to six months

of age, might elucidate the neonatal Sr/Ca pattern.)

240

Based on Figures 7.26 and 7.27, more than half are individuals who died in

childhood: two Postclassic, aged 7-8 and 9 years; and five Historical, aged 6-7 years

(three children) and 8-12 years (2 children). Yet, children only comprise 25% of the total

sample in this study (6 Postclassic and 9 Historical, out of 60 individuals). It appears that

the effect of delaying substantial food supplementation in growing infants may be

increased childhood mortality.

In addition, it appears that Historical individuals are even further delayed than

Postclassic individuals for the age at which Sr/Ca starts to rise considerably. The

following histogram (Figure 7.28) demonstrates the apparent delay among Historical

individuals for the point at which Sr/Ca starts to rise after a period of general stability.

(The “time lag” is not related to dental development time associated with maxillary vs.

mandibular canine sampling. The “delayed” sample is composed of 2 maxillary and 2

mandibular Postclassic teeth and 5 maxillary and 4 mandibular Historical teeth.)

Figure 7.28 Histogram of age of significant Sr/Ca change in “delayed” individuals

Age of Significant Sr/Ca change

in "Delayed" Individuals

0

1

2

3

4

2 2.25 2.5 2.75 3 3.25 3.5 3.75 4 4.25 4.5

Age Interval

Nu

mb

er

of

Ind

ivid

uals

Postclassic

Historical

241

All “delayed” Postclassic individuals display noticeable Sr/Ca increases between 2.5-

3 years of age (2.5, 3, 3, 3), but among Historical individuals, the majority only reflect

significant Sr/Ca change after 3-3.25 years of age (2.25, 2.75, 3.25, 3.25, 3.25, 3.5, 3.5,

3.75, 4.5). One individual, YDL-85/68B is particularly late in Sr/Ca change, not rising

until 4.5 years of age, and is also included in the “stable” pattern below. It is possible

that the consistent Sr/Ca readings reflect: 1) diagenesis, which can result in homogeneous

composition; 2) poor LA-ICP-MS sensitivity (resulting in consistently low values); or 3)

stability after an early rise in enamel Sr/Ca that is not captured by LA-ICP-MS (i.e., from

enamel shortly after birth), which could be attributed to infants who did not breastfeed

(due to maternal illness or death), and who were weaned with maize gruel as neonates.

Once strontium starts to rise, the period required to reach peak Sr/Ca values is

truncated compared to individuals with increasing Sr/Ca from the start of laser sampling

(Figures 7.22-7.23). In the Postclassic sample, this period of rapid food supplementation

and complete weaning ranges from 0.5 years (N10-2/21) to 2.25 years (N10-2/20).

“Delayed” Historical children are completely weaned in 1.0 (most individuals) to 1.75

years (YDL 85/23) after food supplementation increases significantly. (Remember, that

the extended period of low Sr/Ca at the start of each individual probably reflects some

solid food supplementation.) These periods are noticeably shorter than those observed in

individuals with Sr/Ca values increasing from the start of ablation sampling: 2.75 to 4

years among Postclassic individuals and 3 to 4.25 years among Historical individuals (see

above). Obviously, infants who are delayed in substantial solid food supplementation

(i.e., consuming more foods than breast milk) are subject to a faster dietary transition to

solid foods.

242

Stable Sr/Ca

The individuals represented in the “stable” category are distinguished for having low

Sr/Ca ratios throughout the entire ablation period (Figure 7.29). There are some

noticeable fluctuations and slight increases over time, but overall, these individuals

exhibit relatively minimal total change. One Postclassic individual (N10-4/46B) in the

“fluctuating” category (Figure 7.24) also exhibits very low Sr increase (1.084), but is not

included here as enamel could not be sampled from after 3.75 years of age, when further

changes may have occurred.

Similarly, N10-4/11 (Figure 7.29) exhibits some fluctuations, but they reflect only

slight shifts in relative solid food and breast milk intake, with a total increase of just

1.115. It is possible, however, that this female individual experienced a more significant

increase (e.g., 1.5-2.0) in Sr/Ca (food supplementation) earlier in infancy, as enamel prior

to 0.75 years could not be sampled.

Figure 7.29 Graph illustrating Lamanai individuals with stable Sr/Ca over time

Lamanai Individuals with Stable Sr/Ca over time

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

0.16

0.18

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6

Age in years

Sr/

Ca r

ati

o

N10-4/11 YDL 85/50B YDL 85/68B

4% of Postclassic

3% of Historical

243

The two Historical individuals (YDL-85/50B and YDL-85/68B) are noteworthy for

having the consistently lowest Sr/Ca ratios in the entire study sample. In YDL-85/50B,

this is the result of very low Sr readings throughout the entire enamel, rather than high

Ca. This is also the case for the first ablation of YDL-85/68B (approximately 2/3 of the

total crown length), but the remaining ablation of YDL-85/68B (cervical 1/3) exhibits a

low Sr/Ca ratio due to significantly higher Ca values, rather than lower Sr values.

(N.B. Individual YDL-85/68B is also included in the “delayed increase” category since a

late rise in Sr/Ca can be observed after 4.25 years of age [see Figure 7.27].)

It is possible that these three teeth were altered diagenetically, particularly the

cervical third of YDL-85/68B, which is thinner in enamel thickness and may have

undergone calcium enrichment. Nevertheless, White (1986) has previously determined

that diagenesis is not a significant factor for Lamanai skeletons in terms of geological

conditions and burial contexts, particularly regarding calcium: if anything, Lamanai

bones reflect some leaching of calcium.

It is also possible that ICP-MS sensitivity was sub-optimal during laser sampling of

these teeth, resulting in reduced strontium quantification. However, ablation conditions

do not distinguish these teeth from others sampled during the same periods, and other

teeth sampled before and after these teeth do not exhibit such distinctions in Sr and Ca.

Considering the extent of strontium variation in human populations, even within the

same geological locale, the low values of enamel Sr/Ca in these individuals may simply

reflect such diversity. Importantly, it is highly possible that earlier-forming enamel not

sampled by LA-ICP-MS in these individuals, i.e., birth to six months, exhibits an even

more reduced Sr/Ca pattern associated with exclusive breastfeeding. In this case, one can

244

propose that such infants’ mothers may have perished, resulting in their abrupt weaning

with solid food (maize gruel). This sudden transition may have occurred prior to the

period sampled in their enamel (< six months), so that the “stable” patterns captured by

LA-ICP-MS may actually reflect completely weaned infants.

7.6 Determination of Dietary Sr/Ca from Enamel Sr/Ca

In Chapter Four, the Observed Ratio (OR) was outlined, which is used to quantify the

differential distribution of strontium in the food chain (Comar et al. 1957). In this study,

it can express the Sr/Ca relationship between dental enamel and diet since the

discrimination against strontium (“biopurification”) can be quantified as the inverse of

the OR (Elias et al. 1982). To reiterate, Observed Ratio (OR) = Enamel Sr/Ca

Since we have quantified the total Sr/Ca ratio of enamel in this study, the Sr/Ca

signature of the diet at each age category can be extrapolated using Rivera and Harley’s

(1965) calculated OR values for children and adults (Table 7.16).

Table 7.16 Age-related bone-diet observed ratios (ORbone-diet) (Rivera and Harley 1965)

Age in years OR bone-diet

Fetal/newborn 1.00

1 0.60

2 0.24 + 0.08

3 0.25 + 0.09

4 0.24 + 0.09

5 0.23 + 0.08

6 0.21 + 0.07

7 0.20 + 0.06

8 0.19 + 0.05

9 0.18 + 0.05

10 0.18 + 0.04

Adults 0.18

Dietary Sr/Ca

245

Declining OR values (or increasing Discrimination Factor [DF]) over time reflects the

growing discrimination of Sr in favor of Ca as children’s kidneys and digestive systems

mature after the first year of life. While newborns exhibit little or no discrimination of Sr

(OR = 1.0 / DF = 0), due to placental discrimination, OR subsequently declines to 0.6 and

0.2 of the total dietary Sr/Ca thereafter, averaging around 0.18 in older children and

adults (Rivera and Harley 1965).

In this case, Dietary Sr/Ca (age x) = Enamel Sr/Ca

ORbone-diet (age x)

Using this formula, and the age-related OR values of Rivera and Harley (1965), the

dietary Sr/Ca of Lamanai children can be determined from the total Sr/Ca ratios of

enamel at each interval. These data are presented in Table 7.17 below, and graphically

illustrated in Figure 7.30, which includes the Postclassic, Historical and Total Sample

enamel and dietary Sr/Ca values for the period between 0.5 and 5.5 years of age.

Table 7.17 Enamel vs. Dietary Sr/Ca values for Lamanai cohorts at various ages

(OR values based on Rivera and Harley, 1965)

Enamel Sr/Ca (x 10-3

)

Dietary Sr/Ca (x 10-3

)

AGE ORbone-diet Postclassic Historical Total Postclassic Historical Total

0.5-1.0 0.60 0.80 0.63 0.71 1.34 1.05 1.18

1.0-1.5 0.60 0.78 0.69 0.73 1.29 1.14 1.21

1.5-2.0 0.24 0.81 0.72 0.76 3.37 3.02 3.17

2.0-3.0 0.25 0.91 0.78 0.84 3.63 3.14 3.36

3.0-4.0 0.24 1.05 0.90 0.97 4.39 3.73 4.03

4.0-5.0 0.23 1.18 0.98 1.07 5.13 4.28 4.66

5.0-5.5 0.23 1.25 1.01 1.13 5.45 4.38 4.91

246

Figure 7.30 Comparison of enamel Sr/Ca and dietary Sr/Ca in Lamanai cohorts

The pattern of dietary Sr/Ca derived from estimated ORbone-diet values from Rivera

and Harley (1965) indicate that at around two years of age, infant diet is markedly higher

in Sr/Ca content. After the age of two years, with increased strontium discrimination (DF

of approximately 4), inferred dietary Sr/Ca is more than four times higher than the ratio

of Sr/Ca incorporated in enamel. This four to five-fold increase from birth is mirrored in

Sillen and Smith’s (1984: Figure 4) age-specific dietary Sr/Ca values for medieval Arab

bones.

Enamel Sr/Ca vs. Dietary Sr/Ca of Postclassic and Historical cohorts

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

5.5

6.0

0 0.5-1.0 1.0-1.5 1.5-2.0 2.0-3.0 3.0-4.0 4.0-5.0 5.0-5.5 Age Interval

Sr/

Ca R

atio (

x 1

0-3

)

Postclassic Enamel Sr/Ca Historical Enamel Sr/Ca Total Sample Enamel Sr/Ca Postclassic Dietary Sr/Ca Historical Dietary Sr/Ca Total Sample Dietary Sr/Ca

247

It could be speculated that this is the age at which Lamanai children were

supplemented with substantial quantities of solid food. Despite increased gastrointestinal

discrimination of strontium after two years of age (approximately four times that at birth),

continued Sr/Ca rise in canine enamel developing at that age infers a considerable solid

food contribution, or the start of the weaning process. Sillen and Smith (1984) also found

an identical pattern of dietary Sr/Ca change based on bone Sr/Ca, leading them to

conclude that their sample was weaned at two years of age.

However, it should be kept in mind that this pattern is based on Rivera and Harley’s

(1965) estimation of increased radioactive 90

Sr discrimination, or considerably reduced

ORbone-diet, after the age of two years (see Table 7.16). 90

Sr is not a naturally occurring

isotope. This strontium isotope is created by the fission of uranium and plutonium and

was primarily introduced into the atmosphere during nuclear testing in the 1950’s and

1960’s. Ancient Lamanai hard tissues will not contain biogenic levels of 90

Sr. It is

possible that this distinction from 86

Sr may change the current understanding of age-

related strontium discrimination, but there is a lack of evidence in this regard.

In truth, Figure 7.30 only clearly reflects the increased efficiency of strontium

discrimination by the digestive system over time. If enamel Sr/Ca ratios remain stable

over time, or even decline slightly, reduced OR values after 1.5-2 years of age will still

reflect substantially higher dietary Sr/Ca ratios thereafter.

Theoretically, if substantial food supplementation begins after two years of age,

dietary Sr/Ca inferred from enamel values will not reflect the same level of significant

rise as at two years of age. The commencement of significant food intake after two years

of age would not be clearly reflected in dietary Sr/Ca patterns due to the stabilization of

248

(reduced) ORbone-diet after that age. Enamel Sr/Ca values at age three and older would

have to be more than four times higher than two-year-old values to reflect a significant

surge in dietary Sr/Ca that would exceed the rise at two years of age. Conversely, if food

supplementation begins prior to two years of age, it would not be evident. A

significantly reduced OR at two years of age will always indicate a substantial increase in

dietary Sr/Ca at this time.

At this time, however, Rivera and Harley’s (1965) observations on digestive system

discrimination are widely accepted. This implies that Lamanai children were mostly

weaned, or primarily dependent on food, at around two years of age. Inferred dietary

Sr/Ca (Table 7.16) indicates that food supplementation continues to increase steadily

after this age, even beyond five years of age. In general, this pattern does not contradict

other Maya hard tissue evidence (Wright and Schwarcz 1998), ethnohistorical accounts

of Maya weaning, nor ethnographic evidence (see Chapter Five). But, it is probable that

by three to four years of age, most Lamanai infants were eating the maximum amount of

solid food. Breast milk intake may have continued, but it was likely just a minor source

of liquid, and a nutritionally insignificant supplement at that.

Newborn data is not available in this study, but it is expected that the dietary Sr/Ca

ratio and enamel Sr/Ca ratio at this age are the same value, since the ORbone-diet of fetuses

and newborns is 1.00 according to Rivera and Harley (1965). For the Lamanai sample,

this lowest value is likely to be around 0.5 x 10-3

(or lower), and would be comparable to

contemporary values from British bones (0.22 x 10-3

) (United Kingdom Medical

Research Council 1959-1970).

249

The stabilization of high strontium discrimination after two years of age suggests that

hard tissue Sr/Ca thereafter should also level out (or decrease) unless food intake (relative

Sr/Ca) continues to increase significantly. This is not reflected in the Lamanai data.

Discounting diagenesis and instrumentation variables as significant factors influencing

canine enamel Sr/Ca, one can propose that possibly the nature (e.g., rate) of enamel

mineralization after the age of two years (i.e., from approximately mid-crown to CEJ)

amplifies Sr/Ca incorporation beyond levels controlled by gastrointestinal discrimination

(also see Chapter Eight).

Summary

The data indicates that permanent canine enamel does disclose a pattern of Sr/Ca

change that likely reflects the transition from breastfeeding to consumption of weaning

foods. It is posited that hard tissue diagenesis and instrumentation variables are not

significant factors in determining the patterns of Sr/Ca observed in this investigation.

These results represent the first extensive study to quantify Sr/Ca ratios in

sequentially calcifying areas of human enamel. The mean total Sr/Ca values compare

closely with other clinical and nutritional hard tissue strontium data. Importantly, use of

LA-ICP-MS has allowed identification of a continuous pattern of element change and

variation that is not captured in other analytical techniques. The findings are particularly

rich, providing inferences for subtle shifts in diet that can be scrutinized in relation to the

entire period of enamel development and early childhood.

The ability to track detailed life history within individuals is a major outcome of this

investigation, with the recognition of substantial intra-tooth variation in permanent canine

250

enamel. It has revealed that the process leading to complete weaning (breast milk

cessation) is much more complex and variable than the assumed pattern of steady

increase in food supplementation over time. Postclassic and Historical Lamanai

individuals exhibit variations in the ages of peak Sr/Ca values (weaning), rate and age of

food supplementation and patterns of alternating breast milk and solid food consumption.

Where there is significant difference, the consistent finding is that Historical Lamanai

infants experienced an extended period of breastfeeding and delayed food

supplementation compared to their prehistoric counterparts. This factor undoubtedly

contributed to the increased morbidity and mortality of Lamanai Maya during the

colonial period.

The slightly bimodal distribution of peak enamel Sr/Ca (by age) also indicates that

more Historical children may have been weaned much earlier, i.e., younger than three

years of age. The possible reasons for this alternative weaning pattern may be related to

the changing roles of colonial women at Lamanai. In the face of tribute demands, it is

possible that some women may have traded time-intensive childcare (prolonged nursing)

for greater economic production (e.g., cloth, food), resulting in a younger weaning age

for their children. Considering the disparate socioeconomic backgrounds of Postclassic

and Historical period Maya at Lamanai, and the contrasting socio-political climates in

which they lived, the distinctions are not surprising (see Chapter Eight).

Even in cases where significance is not indicated, comparing and shifting total

averaged Sr/Ca patterns for groups of individuals has been worthwhile in constructing

models of ancient infant nutrition. The “adjustment” in total Sr/Ca patterns is not entirely

justified, since most means do not differ significantly and there is considerable variation,

251

but this approach has recognized possible distinctions in cohorts based on age, sex and

time period that correspond with archaeological and ethnographic evidence. In the case

of individuals who died in childhood, a diminished Sr/Ca pattern suggesting delayed

(and/or reduced) food supplementation, reflects a disadvantageous model of infant

nutrition and health that can be associated with shortened lifespan.

The enamel Sr/Ca data presented in this chapter reflects the wealth of life history data

that can be captured by LA-ICP-MS. Dental material provides the ideal canvas for

paleodietary reconstruction and it reflects a high level of sensitivity that can be reliably

associated with developmental age. In Chapter Eight, the possible factors responsible for

the subtle dietary changes inferred by enamel strontium are investigated.

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CHAPTER 8

DISCUSSION

The findings in Chapter Seven attest to the general pattern of increasing strontium

over time that was postulated in this study, and reflect variations in the rate and pattern of

Sr change that have multiple implications. Based on the results, five major issues are

elaborated in this chapter:

1) Comparative data regarding strontium composition of breast milk vs. weanling

foods is examined, including the effect of alkali processing on maize and hard

tissue Sr/Ca values.

2) The inferences for ancient Maya infant nutrition are discussed and evaluated

within the framework of known weaning behavior.

3) The implications for infant nutrition are then contextualized within the

Postclassic and colonial histories of Lamanai, to better understand the factors

that affect maternal childcare practices and infant health. These include

comparisons of enamel strontium between children and adults and between

males and females.

4) To broaden the perspective, the results are compared to other hard tissue

strontium data and the role of strontium analysis in paleodietary reconstruction

is assessed.

5) Finally, analytical issues of this study are examined to formulate a set of

recommendations and considerations for future enamel research using LA-ICP-

MS technology, as well as further research that can arise from this study.

253

8.1 The Implications of Maize Processing for Dietary Reconstruction

For the ancient Maya, examining the transition from breast milk to solid food intake

and weaning means that the relative Sr/Ca signatures of human breast milk, maize gruel

and other presumed weanling foods must be understood. Universally, non-milk weanling

foods, or beikost, are easily digestible forms (gruel or porridge) of starches such as maize,

wheat or rice. Children are also often supplemented with soft fruits and vegetables, eggs,

bread or tortillas, as well as regurgitated adult foods and even ale (Fildes 1986, 1988;

Stuart-Macadam and Dettwyler 1995).

Based on ethnographic analogy and historical documents at the time of contact, it is

probable that Lamanai Maya infants consumed alkali-processed maize gruel (atole) or

other softened maize products (e.g., soaked tortillas) during the weaning process (Behar

1968; Benedict and Steggerda 1937; Izurieta and Larson-Brown 1995; Landa in Tozzer

1941). Bone isotopic evidence (13

C) verifies this and indicates that children consumed

high levels of maize that are comparable with adults throughout the Postclassic and

Historical periods (White 1986).

Like Maya adults, and probably more so, maize comprised the bulk of their diet,

depending on relative breast milk intake, with possible intake of other foods such as

fruits, vegetables (beans or squash), and possibly even regurgitated meat from parents.

White (1986) notes that bone chemical evidence does not indicate the consumption of

beans and/or meat in Lamanai weanlings, but contemporary information on Guatemalan

Ladinos includes small quantities of softened corn tortillas and black bean broth as a

weanling supplement after six months of age (Izurieta and Larson-Brown 1995). As a

major Maya food staple even in ancient times, it is likely that Lamanai infants consumed

254

similar bean products, but it is reasonably assumed that maize products represent the

majority of the weanling diet.

On the surface, the nature of Sr/Ca patterns suggests that most Lamanai Maya infants

were weaned onto maize that was not processed with lime to produce a calcium-rich

atole. This verdict is based on Burton and Wright’s (1995) observations that alkali-

treated maize becomes so enriched with calcium that the Sr/Ca signature of raw maize

becomes “invisible” under the weight of added calcium. The appearance of rising Sr/Ca

values in enamel sampled in this study contradicts this finding.

Yet, it must be remembered that Lamanai mothers are also producing extremely low

Sr/Ca breast milk as a result of consuming reduced Sr/Ca lime-processed maize

throughout their life. With mammary gland discrimination, Maya breast milk Sr/Ca will

still be reduced compared to maize foods that are processed with lime.

In a study tracking the childhood introduction of maize in enamel Sr/Ca, several

fundamental details should ideally be known. These include the relative strontium and

calcium content of: 1) the breast milk of Maya mothers eating a traditional diet; 2)

ancient Lamanai raw maize; 3) traditional weanling foods, in this case, atole (lime-treated

maize gruel); and 4) local soil and water. Based on such data, one needs to assess the

nature of two main relationships: a) the difference in Sr/Ca between human breast milk

and processed maize atole (weanling gruel) (to track the start of supplementation after

exclusive breastfeeding); and b) the effect of consuming lime-treated atole on dental

enamel composition.

Essentially, in order to observe a trophic level effect indicative of solid food (maize)

intake after exclusive breastfeeding, the Sr/Ca ratio of weanling gruel, which was likely

255

treated with lime, would have to be significantly higher than the relative Sr/Ca of breast

milk. Maize atole elemental composition is not known, but one can apply the strontium

and calcium values of other treated maize products, i.e., tortillas (Wright 1994).

Unfortunately, because breast milk, hard tissue and dietary elemental composition

will be wholly dependent on the local water and food growing conditions (soil and

water), there is limited reference data that can be accounted for here. Firstly, there is no

comparable data for the Sr/Ca content of breast milk from women consuming a strictly

traditional Maya diet. There is also no available data for the composition of ancient

maize from Lamanai, but in this case, dietary elemental composition can be inferred from

other Maya sources.

Importantly, since Lamanai mothers would have consumed very low Sr/Ca processed

maize, which would be further fractionated in their breast milk due to mammary gland

discrimination, we can correctly assume that the lime-processed maize gruel consumed

by their infants will still be enhanced in Sr/Ca compared to breast milk. Strontium

concentration in human breast milk has been found to vary from 0.14-0.35 mg Sr / g Ca,

or a Sr/Ca ratio of 0.14 to 0.35 x 10-3

(Harrison et al. 1965; Krachler et al. 1999;

Rehnberg et al. 1969; Rosenthal 1981). The variation can predominantly be attributed to

differences in water and food composition, but it does not include Maya individuals

consuming a traditional diet. Lacking such specific data, this range nonetheless forms the

basis of comparison with maize Sr/Ca and hard tissue composition in this study.

Regarding maize, White (1986) has noted that, on average, raw maize is composed

of 7.5 mg of calcium per 100g, or 75 ppm. In contrast, lime-soaked, and lime-soaked and

boiled, maize returns calcium values ranging from 370-2404 ppm, in experiments

256

undertaken by Wright (1994: Appendix F). For this study, it would be useful to know the

Sr/Ca composition of ancient Lamanai maize, as well as the relative strontium and

calcium contents of maize samples before and after lime treatment, but this is not

available. Consequently, maize strontium composition is inferred by geological factors

(soil, water), experimental tortilla research, as well as extrapolation from enamel Sr/Ca

using known levels of strontium discrimination (inverse of OR).

An important consideration in maize composition and processing is water. As in

food, strontium varies widely in water supplies, depending on geology (see Chapter

Four). Maize Sr/Ca composition will be directly influenced by water and soil chemistry.

The relative Sr/Ca abundance of local water is particularly significant because strontium

is known to be one of the few elements that are absorbed by vegetables from cooking

water (Losee and Adkins 1968).

Alkaline elements are more completely absorbed from liquids, particularly milk, than

from solid food (Marcus and Lengemann 1962). So while the Sr composition of maize at

Lamanai must be accounted for, the Sr content of local water is equally important

because infants are mainly eating watery gruel as a supplement. Contemporary evidence

also indicates that maize atole is frequently cooled with fresh water prior to feeding,

which results in a further diluted (and possibly strontium-enriched) gruel (Izurieta and

Larson-Brown 1995). However, while boiling maize and adding cool water will result in

a potentially strontium-rich watery gruel, calcium is also enhanced in the same manner,

maintaining the relatively low Sr/Ca signature.

Unfortunately, no site-specific water values are available for Lamanai, but local soil

Sr/Ca can be used to infer the relative composition of water and give an indication of

257

maize values, which is assumed to generally resemble the soil. The weathering of

limestone bedrock at Lamanai would have supplied most of the Sr and Ca that entered the

water and soil systems at the site (Wasserman et al. 1977). However, despite having high

Sr concentration, limestone has a relatively low Sr/Ca ratio due to the high abundance of

Ca, while shales and granites have the highest Sr/Ca ratios (Turekian and Kulp 1956a).

White and Schwarcz (1989: Table 2) have reported on the element composition of

some soil samples from Early Classic to Historical archaeological contexts at Lamanai.

Soil Sr/Ca ratios range from 0.737 to 1.045 x 10-3

(see Table 8.1 below), with a mean

ratio of 0.880 x 10-3

. As expected, bone Sr/Ca values are lower and range from 0.417 to

0.752 x 10-3

, averaging 0.529 x 10-3

, according to White and Schwarcz (1989: Table 2).

Table 8.1 Relative Sr and Ca data for Lamanai bone and soil samples

(based on raw data of White and Schwarcz 1989: Table 2)

Time Pd.

Structure

No.

N

Sample

Type

Sr

(µg/g)

Ca

(g/kg)

Sr/Ca

(x 10-3

)

Postclassic

N10-2

5

X bone

112.2

203.99

0.550

1 Soil 48.3 50.62 0.954

N10-3 1 Bone 87.5 198.87 0.440

1 Soil 65.6 78.57 0.835

N10-9 1 Bone 99.1 204.11 0.486

1 Soil 57.3 77.79 0.737

N11-5 1 Bone 154.2 205.14 0.752

1 Soil 52.9 50.62 1.045

Historical

YDL

5

X bone

84.7

203.35

0.417

1 Soil 51.6 62.09 0.831

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White and Schwarcz’ (1989: Table 2) element data for Lamanai human bone and soil

samples indicates that bone Sr/Ca values are 1.28 to 2.75 times lower than soil values. In

comparison, enamel strontium composition is generally five times lower than dietary

Sr/Ca in adults (see above). But these soil strontium values are similar to mean soil

values observed by Wright (1994) for ancient Maya sites in Guatemala, which are, on

average, 1.53 times lower than bone Sr/Ca (see Table 8.2).

Table 8.2 Mean bone and soil Sr/Ca of Pasion Maya sites in Guatemala

(derived from raw data of Wright 1994: Appendix G)

Sample

Type

N

Mean Sr/Ca

(x 10-3

)

S.D.

(x 10-3

)

Range

Bone Ash

117

0.413

0.226

0.134-1.357

Soil 84 0.630 0.503 0.254-2.676

Based on strontium and calcium values observed by Wright (1994: Appendix G) for

remains from various sites in the Pasion region, Guatemala, other ancient Maya bone

Sr/Ca ratios range from 0.134 to 1.357 x 10-3

(which excludes one sample with a Sr/Ca

ratio of 3.699 x 10-3

). Wright’s raw data reflects the enormous variation that

characterizes human hard tissue and soil composition, particularly from different

geological and temporal origins. At the same time, it resembles the range of Sr/Ca values

observed in this study for Lamanai teeth: average enamel Sr/Ca values range from 0.631

to 1.254 x 10-3

, depending on age (see Table 7.4).

259

Wright (1994: Appendix D) has reported on the composition of one raw maize cob

from Altar de Sacrificios (Guatemala), which has a Sr/Ca ratio of: 1.13 x 10-3

. No other

data for maize Sr/Ca from the Maya area has been located in the literature, but LaVigne

(2002) has determined a mean Sr/Ca value of approximately 2.51 x 10-3

for six modern

unprocessed maize (kernel) samples from central Mexico. By inference, Lamanai soil

Sr/Ca values ranging from 0.737 to 1.045 x 10-3

(White and Schwarcz 1989: Table 2)

suggest that unprocessed maize Sr/Ca is likely not higher than 1.0 x 10-3

at the site, but

these samples derive from cultural contexts and do not necessarily reflect the Sr/Ca

values of agricultural fields.

It should be noted that strontium values vary significantly between plant parts, due to

differential discrimination, i.e., greater accumulation in roots and stems (Runia 1987b).

Plant roots, root crops and cereal grains have the highest Sr/Ca ratio, with values 1.5-10

times higher than leaves or shoots, which usually resemble soil levels (Runia 1987b).

Maize kernels and the cob likely differ in Sr/Ca ratio, suggesting that LaVigne’s kernel

average may be closer to the composition of dietary maize at Lamanai, but the efficiency

of strontium discrimination in maize species and the extent of differences between maize

parts are not known (see Burton et al. 1999).

Assuming that alkali treatment will reduce the Sr/Ca ratio by approximately six to

twenty times, or greater, Wright’s maize value is reduced to a range of 0.056 to 0.188 x

10-3

for lime-processed maize. LaVigne (2002) has similarly reported on Sr/Ca values of

six lime-treated tortillas from Solis, Central Mexico, averaging 0.176 x 10-3

(compared to

2.51 x 10-3

for raw Solis maize).

260

However, in laboratory experiments simulating alkali-processing, using comparable

Solis maize and cal (lime solution), LaVigne found that processed maize Sr/Ca reached a

mean of 1.3 x 10-3

(n=6). This value derives from kernels softened with lime, after

removal of the pericarp. Based on this finding, one can only assume that the process of

tortilla-making (including toasting on a comal, or griddle) entails changes in chemical

composition, i.e., dramatically reduced Sr/Ca, that do not resemble the chemistry of

alkali-processed maize at an earlier stage of preparation.

This higher ratio (compared to tortilla Sr/Ca) reflects a potential difference in the

Sr/Ca values of other traditional maize foods such as weanling gruel. Furthermore, the

dilution of maize dough with water, to produce gruel, provides an additional source of

strontium that could result in a food enriched in Sr/Ca compared to tortillas. Without

analysis of such watery maize food, which was the primary Maya weanling supplement,

one cannot assume that tortilla Sr/Ca values will infer the relative Sr/Ca of weanling

gruel. Importantly, this value is significantly higher than the Sr/Ca range of human breast

milk: 0.14 to 0.35 x 10-3

(Krachler et al. 1999; Rehnberg et al. 1969; Rosenthal 1981).

Elsewhere, Sr/Ca values of some raw maize in the United States average around 7.14

x 10-3

(Shacklette 1980; Watt and Merrill 1963), which is significantly higher than the

values of the raw Altar de Sacrificios and Solis maize. If one refers to the North

American raw maize Sr/Ca value, one arrives at hard tissue Sr/Ca ratios ranging from

4.28 x 10-3

at 0.5 years, 1.78 x 10-3

at 3.0 years and 1.64 x 10-3

at 5.0 years of age, using

Rivera and Harley’s (1965) age-specific OR values for Sr discrimination.

For Lamanai Maya, mean enamel Sr/Ca ratios range from 0.63 x 10-3

(Historical

cohort at 0.5-1.0 years) to 1.25 x 10-3

(Postclassic cohort at 5-5.5 years), which infers

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dietary Sr/Ca values of 1.05 to 5.45 x 10-3

based on discrimination factors (see Table

7.17). The low end of this range resembles LaVigne’s (2002) Sr/Ca values for lab-

simulated central Mexican maize: 1.3 x 10-3

, as well as unprocessed maize: 2.51 x 10-3

.

The inferred Lamanai dietary Sr/Ca values are reduced compared to the 7.14 x 10-3

ratio observed by Shacklette (1980) and Watt and Merrill (1963) for North American

maize. This may suggest that the maize consumed by Lamanai infants was indeed treated

with lime to reduce the Sr/Ca ratio. But compared to the maize Sr/Ca derived from

Wright (1994), and especially the Sr/Ca range of treated maize after calcium enrichment

(0.056 to 0.188 x 10-3

), extrapolated Lamanai maize values are noticeably higher.

Yet, Wright’s (1994) bone Sr/Ca data also infers higher dietary Sr/Ca values than

those of lime-treated maize, ranging from 0.223 to 2.262 x 10-3

at 0.5 years (OR=0.60) to

0.583 to 5.900 x 10-3

at 5.0 years (OR=0.23). The range reflects sample variation (bone

Sr/Ca of 0.134 to 1.357 x 10-3

) and, as age is not specified, also accounts for different

levels of strontium discrimination (OR value). Clearly, the Sr/Ca values suggest that

hard tissue composition is inflated compared to the hard tissue values that should

theoretically arise from dietary components such as maize tortillas, based on human

strontium discrimination (OR).

Since enamel Sr/Ca ratios observed in this study fall within the range of bone and

dental values outlined in Chapter 8.5, one can propose several explanations for the

discord between treated maize values and theoretical food values derived from hard

tissues. Firstly, it is possible that the discrimination factors observed for strontium and

human metabolism are inaccurate. It is noted that Rivera and Harley (1965) and others

measured such levels of discrimination using 90

Sr, which is not a naturally occurring

262

isotope, but one produced from the fission of uranium and plutonium (nuclear testing).

Human gastrointestinal discrimination of naturally-occurring isotopes such as 86

Sr may

differ from cited OR values because of this distinction.

Second, accompanying the reductions in rates of enamel secretion and mineralization

that have been observed in some permanent teeth in the mid-crown to cervical regions

(see Chapter Three and Appendix A), it is possible that such changes also enhance Sr/Ca

incorporation in such enamel, i.e., after 2-3 years of age. This would explain the

continued rise in enamel Sr/Ca after two years of age, despite stabilization of high

gastrointestinal discrimination, and result in a lowering of the inferred dietary Sr/Ca.

Unfortunately, the current state of enamel mineralization research cannot confirm this

supposition, but the evidence overwhelmingly indicates that enamel Sr/Ca does continue

to rise after maturation of digestive systems.

While the enamel and inferred dietary data suggest otherwise, it cannot be assumed

that Lamanai maize was not treated with alkali because we do not know the typical

strontium and calcium values for Lamanai water, breast milk, maize and weanling diet

(atole). The extent of strontium enrichment associated with boiling of maize with

Lamanai water and the addition of water prior to consumption would be informative in

this respect. Other sources of strontium that could contribute to total hard tissue Sr/Ca

include native salts (critical for adequate nutrition and biological function), as well as the

clay of cooking and serving vessels, which are additional strontium sources in Hopi diet

(Kuhnlein and Calloway 1979).

It is possible that consumption of other higher Sr/Ca foods (e.g., mashed raw maize,

beans, other raw fruits or vegetables) might account for an elevated strontium input.

263

Importantly, experiments by LaVigne (2002) suggest that tortilla Sr/Ca values may be

reduced compared to other alkali-processed maize foods (e.g., mashed maize, dough,

gruel). Weanling foods, in the form of watery gruel, likely have enriched Sr/Ca values

compared to experimentally tested (modern) tortillas. Additionally, the total dietary Sr

could be elevated if maize intake is temporarily withdrawn or dramatically reduced,

relative to consumption of other (higher Sr/Ca) foods.

It is highly likely that Lamanai children were weaned on a diet almost entirely

composed of maize products. Bone chemical evidence suggests that up to two-thirds or

more (70%) of the Lamanai adult diet consisted of maize (White 1986). Since adults

consume relatively more meat and non-maize foods than children, it is not implausible to

attribute a predominantly maize diet to children, who also probably consumed some high

strontium foods such as raw fruit and, possibly, untreated mashed maize.

In the end, enamel should reflect a clear Sr/Ca rise in regions developing after the

start of food supplementation and exclusive nursing because, despite alkali processing of

maize, and a reduced Sr/Ca signal, mothers are consuming the same low Sr/Ca maize.

Maternal tissues will reflect this very low Sr/Ca value, with mammary gland

discrimination actually producing breast milk that is further reduced in relative strontium

composition.

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8.2 Sr/Ca Behavior in Lamanai Permanent Canine Enamel

Several factors support the assertion that enamel Sr/Ca captured in this investigation

faithfully records a biogenic signal associated with childhood dietary intake:

1) enamel is highly resistant to diagenetic processes and can be relied upon to reflect

strontium incorporation during mineralization

2) hard tissue strontium is a very reliable indicator of dietary intake of strontium

during tissue development

3) Sr and Ca counts (and relative Sr/Ca) of enamel at the termination and start of

consecutive rasters within a single tooth are consistent, therefore discounting

instrumentation variables as the source of rising Sr/Ca over time (see Section 8.5)

4) enamel Sr/Ca patterns and dietary behavior associated with strontium change

correspond well with known childcare traditions, particularly the significant

increase in enamel Sr/Ca (food initiation) after six to nine months of age, and

attainment of peak Sr/Ca (weaning) between three and five years of age

The results of this analysis suggest that relative strontium abundance can be

recognized in permanent canine enamel in patterns that likely reflect dietary intake during

early childhood. From an archaeological perspective, understanding the diet and weaning

patterns of children at this critical stage can provide valuable inferences for the impact of

social change on biology.

In respect of their study on Medieval British skeletons, Richards and co-authors

(2002) have stated that for hard tissue-based research on infant weaning to be valid,

several criteria must be demonstrated: 1) a culturally determined age of weaning that is

observed by all members of the sample; 2) weaning that is relatively abrupt (i.e., a few

265

months); and 3) children were weaned onto foods similar to the adult diet. The results of

their investigation confirm all of their assumptions.

Here, however, enamel Sr/Ca data reflects important deviations. An alternative

weaning model can be constructed from the LA-ICP-MS analysis of Lamanai enamel,

and it is characterized by 1) variations in the age of maximum Sr/Ca values, or presumed

weaning age; 2) an extended period of gradual food supplementation; and 3) periods of

fluctuating Sr/Ca reflecting alternating breast milk and solid food intake, or fluctuations

in the types of weanling foods, i.e., due to seasonal availability, crop failure, food taboos

during illness.

While most teeth in this study exhibit an increasing Sr/Ca signature over time, many

Postclassic (31%) and Historical individuals (38%) are noteworthy for Sr/Ca patterns that

fluctuate. Besides reflecting variations in absorption and hard tissue incorporation, the

prevalence of gross fluctuations in enamel Sr/Ca pattern also likely reflects significant

cultural and biological changes in Lamanai society. Fluctuations in food intake, relative

to breastfeeding, may be related to pervasive illness and/or disruptions in access to food.

Furthermore, children’s nursing may be interrupted by the addition of subsequent

siblings, since many cultures view the breast milk of pregnant mothers as “unhealthy”

and inappropriate for consumption (see Chavez and Martinez 1982; Institute of Medicine

1991; Stuart-Macadam and Dettwyler 1995; among others).

Beyond availability, cultural perceptions or taboos against “contaminated” solid food

intake during illness (which is often associated with gastrointestinal disorders) might also

account for occasional food withholding, as observed in many societies (Dettwyler and

Fishman 1992; Fildes 1986; Stuart-Macadam and Dettwyler 1995; Wood 1983). In this

266

context, Dettwyler and Fishman (1992) observed the delay of any solid food

supplementation for up to a year or more. In some cases, undernourished and

underdeveloped children are nursed longer because mothers associate increased mortality

risk with the period after weaning (Caulfield et al. 1996; Simondon and Simondon 1998).

In contrast to the general model of steady, gradual, food supplementation until

weaning, the variation in canine Sr/Ca in both the Postclassic and Historical periods

indicates that weaning behavior at Lamanai was highly flexible and subject to subtle

changes. Enamel strontium clearly reflects a combination of: a) the adaptability of

children to changing socio-economic and epidemiological conditions, which is dependent

on maternal childcare practices; b) different diet and health histories of colonial Maya

children originating from elsewhere in the Maya Lowlands, as well as local children; and

c) variations in hard tissue element incorporation.

Enamel isotopic values analyzed by Wright and Schwarcz (1998) also reflect

considerable variation in the duration of lactation, which they attribute to variations in

child growth, nutritional demands, “maternal competence”, socio-economic factors and

temporal shifts in diet. Undoubtedly, these fluctuations reflect human adaptations to

changing nutritional, ecological and socioeconomic conditions, particularly during

colonial times.

Although hard tissue strontium cannot directly indicate the cessation of breast milk

intake, if one surmises that peak Sr/Ca followed by stable and/or decreasing values can

infer the period of maximum solid food intake (weaning), the Lamanai data indicate that

this transition is relatively late in both Postclassic and Historical Maya. In general, the

Lamanai weaning pattern is characterized by 1) dietary supplementation starting in the

267

first year, particularly by 0.75 years (9 months) of age; 2) gradual food supplementation

that accelerates after two years of age; and 3) breast milk intake that continues up to five

years of age.

Based on clinical data (Buckley 2001), it is likely that breast milk intake remained

high for the first two years, and then significantly decreased after three years of age,

when breastfeeding typically decreases in frequency and length of feedings. Further, the

results suggest that Richards and colleagues’ condition for a culturally determined

weaning age is not entirely appropriate for the ancient Maya, where infant feeding varied

a great deal within a general model of extended nursing.

Time of weaning across human cultures is highly variable and specific to each

family’s circumstances. Mothers, fathers and children are all active agents in the process.

Factors that influence the termination of breastfeeding include cultural perceptions of

milk quality or quantity, maternal illness, resumption of menses, birth of another child,

anxiety and emotions of the mother, economic changes (work responsibilities), social

trends (e.g., female body image and fashion), socioeconomic status, seasonal time of

year, infant’s age, tooth eruption, child’s bowel development and general health (Carballo

and Pelto 1991; Fildes 1986).

An important factor in the timing of weaning is illness. Withholding of food and

exclusive nursing has been associated with childhood illness, but sick children may also

cease breastfeeding due to an inability to suckle, or separation from their mothers. In this

case, extended exclusion of breast milk often results in the weaning of the child, due to

the mother’s inability to produce milk without suckling stimulation (or manual

expression), and the infant’s adjustment to solid foods. Thus, child illness may lead to

268

weaning, rather than the cessation of breastfeeding causing illness (see Institute of

Medicine 1991).

Numerous lines of evidence support an extended breastfeeding pattern in ancient

times (see Chapter Five). Many cultures attribute extended nursing, i.e., more than two

years, to greater child survival (see Fildes 1986). Besides contact period ethnographic

observations of infant nursing until three to four years of age (Landa, in Tozzer 1941),

extended breastfeeding among the ancient Maya is substantiated by contemporary

evidence: the mean duration of breastfeeding in indigenous Guatemalan (Maya)

communities is two years (Wright and Schwarcz 1998), while Guatemalan Ladinos

breastfeed for an average of 15 months (Izurieta and Larson-Brown 1995). Hard tissue

evidence of chronic infectious diseases, in the form of porotic hyperostosis and enamel

defects, particularly during the Historical period at Lamanai, is likewise associated with a

late (common) weaning age between two and six years of age (White et al. 1994).

8.3 The Nature of Ancient Maya Health and Nutrition at Contact

Significantly, the enamel strontium data reflects important temporal differences

between the prehistoric and historical populations at Lamanai that serve to enrich the

archaeological understanding of the contact experience. Most notably, Historical

Lamanai children were more susceptible to dietary fluctuations (inconsistency), and

experienced delayed food supplementation compared to their Postclassic counterparts.

Throughout the colonized New World, a soaring mortality rate was the gravest

consequence of contact. Contributing factors include introduced epidemics, violence,

increased infant mortality, reduced birth rates, female infertility, forced resettlement,

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socio-economic reorganization and the overall effects of a perilous disease environment

(see Chapter Two).

Reflecting this turbulent era, the Postclassic and Historical Lamanai samples differ in

the mean Sr/Ca ratio of enamel at all intervals between 0.5 and 5.5 years of age, as well

as the extent of variable Sr/Ca patterns. For instance, at all age intervals, Historical

males exhibit reduced Sr/Ca ratios compared to Postclassic males, particularly after the

age of 2.25 years of age (Section 7.3). After this age, Historical males may have been

delayed in reaching comparable Postclassic values by up to 1.5 years, suggesting that

Historical male toddlers consumed relatively less solid food than prehistoric boys of the

same age.

Postclassic and Historical females reflect the most differences in mean Sr/Ca, with

Postclassic girls having higher enamel Sr/Ca at every age (Figure 7.13). Adjusting

strontium patterns indicates that Historical individuals may have required up to 2.25

years to attain comparable Sr/Ca values as Postclassic individuals. It is proposed that the

reduced mean Sr/Ca pattern in Historical individuals, and delayed food supplementation

compared to prehistoric Maya, reflects important cultural responses to colonialism at

Lamanai.

Interestingly, Lamanai bone composition data supports this finding. White and

Schwarcz (1989: Table 1) report a mean Sr value of 111.7 ppm (0.1117 x 10-3

) for 17

Post Classic individuals (mixed adults and juveniles) and 83.1 ppm (0.0831 x 10-3

) from

10 mixed Historical individuals. (This is at the lower range of mean bone strontium

abundance: 150-250 ppm in bone ash [Aufderheide 1989].) Mean Sr/Ca ratios for

Lamanai bone reflect the reduction from Post Classic to Historical times: approximately

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0.225 x 10-3

(0.000225) in the Postclassic (N=17) and 0.205 x 10-3

(0.000205) in the

Historical cohort (N=10).

With Spanish rule, Maya populations were forced to pay tribute in the form of

material products and labor. More so than men, whose domain was principally the milpa

and hunting grounds, Maya women fulfilled this role because most demanded goods were

produced in the domestic sphere, i.e., kitchen garden produce, hens, honey, beeswax, and

especially cotton mantas (Clark and Houston 1998; Clendinnen 1982, 1987; Restall

1995).

In the colonial Maya household, women assumed mounting economic and domestic

responsibilities. Besides the traditional female role of household maintenance (cooking,

hygiene), kitchen gardening and childcare, Maya women were also responsible for

weaving, flour-grinding, raising animals for consumption and exchange, market

commerce, tribute payments and even direct labor tribute, i.e., domestic services in

Spanish establishments and households (Clark and Houston 1998; Clendinnen 1982;

Hunt 1974; Landa in Tozzer 1941; Restall 1995; Schroeder et al. 1997; Vail and Stone

2002).

Since their duties were mostly situated in a domestic context, many colonial Lamanai

women were able to sustain time-intensive childcare practices such as extended nursing.

Inconsistent resource availability (see below) likely contributed to the maintenance of

extended nursing in most children, yet, at the same time, greater incidence of peak

enamel Sr/Ca at earlier ages in the colonial cohort also suggest that more Historical

women weaned their children earlier. This behavior would be an expected outcome of

increased female labor and economic responsibility.

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Extending into contemporary times, female work obligations continue to have

significant repercussions for infant care and health. In many societies, a market economy

leads to reduced breastfeeding among working women, increased use of substitute foods

(formulas), earlier infant weaning, increased infant mortality and even reduced fertility

(e.g., Chandra and Lakshmiswaramma 1991; Swedlund 1990; Swedlund and Ball 1998).

Like colonial Lamanai families, the movement of contemporary populations from rural to

urban settings also results in the disintegration of extended kin networks and integral

support systems.

Women are not visible in the historical record at Lamanai, but Lamanai women likely

assumed these roles too, since the site continued to participate in the exchange of goods,

which now included European products, with Spanish authorities and Maya merchants

trading between the Yucatan and the southeastern frontier (Graham et al. 1989). Colonial

Lamanai women were burdened with more responsibilities compared to pre-contact times

and childcare was often modified to accommodate the change, entailing either delayed

food supplementation or earlier weaning.

As Graham (1991: 333) has eloquently stated, colonial period Maya women acted as:

communicators of cultural information to children, as filters of Spanish ideas and

processors of new information, as dietary planners and maintainers of health and

hygiene, and as wives, advisers, and companions of the first Spaniards-the primary

weavers of the first tapestry to include threads of Old and New World cultures.

With an increase in the domestic workload of Maya women during colonial times, it

was often their bodies that suffered the physiological consequence. Being bearers of

future generations was probably the greatest health risk. Based on historical accounts

(Maya testators) and rates of infant and adult mortality, it is likely that, on average, Maya

272

women delivered at least four children in the mid-17th

century and more than eight by the

end of the colonial period, with a child survival rate of 50% (see Restall 1995).

As evident throughout the New World after contact, indigenous women’s health often

deteriorated with the added stresses of famine, infectious disease, social breakdown and

economic hardship (Cook 1998; Farriss 1984; Graham 1991; Larsen and Milner 1994;

Stannard 1990, 1991; Verano and Ubelaker 1992; White et al. 1994). Introduced diseases

that were devastating in their effectiveness include smallpox, measles, influenza,

tuberculosis, bubonic plague, typhus, cholera and yellow fever.

Lamanai Maya were also increasingly anemic in colonial times, as reflected in greater

rates of porotic hyperostosis (White 1986; White et al. 1994). No gender or age (adult

vs. child) differentiation was noted. Among women, this may have arisen from a

combination of helminthic or other parasitic infections, heavy reliance on an iron-poor

maize diet, excessive fluid loss from the tropical climate, monthly blood loss and/or the

physiological demands of pregnancy and lactation (White 1986; White et al. 1994).

Among children, the primary causes were probably parasitic infections (e.g., dysentery,

malaria, hookworm) and weanling diarrhea, combined with an iron-poor maize diet

(White 1986), which synergistically interact to exacerbate each condition.

As the most vulnerable members of society, Lamanai children, particularly of

weaning age, best reflect the changing epidemiological conditions of the colonial period.

At Lamanai, children experienced significantly higher rates of infection after contact.

Hard tissue evidence of more severe, acute, and episodic health stress among children

during colonial times includes microscopic enamel defects, or Wilson bands, which are

three times more prevalent in colonial remains (Wright 1990).

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An important contributing factor to rates of infection and public health is poor

hygiene in crowded or unsanitary living conditions. Records in 1637 suggest that

Lamanai was sparsely inhabited in later colonial times, with a population of only 72

Maya (Jones 1989), but this is not necessarily indicative of the community just before

and after contact (White et al. 1994). Remember too, that colonial Lamanai was a

community in flux, with settlement that was scattered and impermanent in nature, both in

terms of population composition and architecture (Graham et al. 1989; Pendergast 1982).

In this context, it is likely that public hygiene, in the form of waste and water

management, was not regularly maintained. Weather cycles, i.e., the rainy season, would

have also increased the environmental pathogen load for several months of each year.

These conditions and the congregation of Maya from other areas that were disease-

affected (e.g., Yucatan) would have nurtured the transmission of infectious illnesses. In

extreme cases, the combined effect of infectious disease and malnutrition is a failure to

meet the increased physiological requirements of growing children during the weaning

period (Mata 1990; Mata et al. 1977; Rivera and Martorell 1988a, b; Scrimshaw 1978;

Scrimshaw et al. 1968; White et al. 1994; Wood 1983; among others).

Notwithstanding epidemiological conditions, the weaning transition is undisputedly a

critical stage of childhood. A marginal diet is an important factor. Unfortunately,

weanling foods are commonly deficient in protein and low in total energy, as well as iron

content, in the case of maize. The process can be traumatic and stressful and children

often experience separation anxiety, wasting and gastrointestinal disorders. In the event

of abrupt weaning, either due to social trends (e.g., among British and American

colonies) (Fildes 1986), or maternal illness or death, children are especially affected.

274

Common ailments often associated with the weaning process include diarrhea,

undernourishment (e.g., protein deficiency), vomiting, rickets, scurvy and infection. This

is manifest as greater rates of hard tissue pathology, particularly enamel defects, during

weaning (i.e., 2-4 years of age) (Cohen et al. 1994; Danforth 1989, 1997; Saul 1972;

Song 1997; White 1986; Whittington 1992; Wright 1990).

“Weanling diarrhea” is an important disease of childhood that has extensive

ramifications for growth and development (Scrimshaw et al. 1968). The clinical data

overwhelmingly demonstrates that it is a major source of infant morbidity and its role in

infant health and survival cannot be overstressed (Brown et al. 1989; Chen and

Scrimshaw 1983; Martorell et al. 1975; Mata et al. 1967; Mølbak et al. 1994; Sabin 1963;

Scrimshaw 1978; Walker-Smith and McNeish 1986, among others).

Spanish domination also degraded the health of women and children in other ways

related to social cohesion. Concomitant with Christianizing efforts, the traditional Maya

family structure and (multi-) household organization, which was virilocal (centered on

the husband’s family), polygamous and extended, was forcibly reduced to a Spanish

model of single nuclear families (Landa, in Tozzer 1941; Clendinnen 1982; Restall

1997). This disruption removed the familial support system, with its extensive physical

and psychosocial benefits, and further taxed a women’s time, her ability to fulfill multiple

domestic and economic roles, her health, and the health and care of her children. With a

permanent Spanish presence at the site, such domestic turmoil was likely reproduced at

Lamanai (Graham 1991).

Nevertheless, despite their subordinate social position in Maya and Spanish society,

Maya women were known to actively and passively challenge Spanish and Christian

275

authorities in many ways (Clendinnen 1982; Restall 1995; Schroeder et al. 1997). In fact,

their significant role in cotton cloth production and the colonial economy actually

enhanced their value in society to an extent, even giving them credence with legal matters

(e.g., inheritance) and social complaints in the Yucatan (see Restall 1995).

At Lamanai, enamel Sr/Ca suggests that Maya women may have also resisted Spanish

demands on their time by maintaining intensive childcare practices such as prolonged

breastfeeding. Despite increased demand on their time, colonial Lamanai women were

probably able to breastfeed for extensive periods because their responsibilities remained

largely within the domestic sphere.

Resistance might also extend to maintaining a traditional Maya diet, which is

indicated by bone chemical (White 1986) and faunal evidence (Emery 1999). Cross-

culturally, many societies actively express their identity and resistance to hegemony and

social change through specific food consumption behavior (e.g., Brown and Mussell

1984). In the Yucatan, ethnohistorical documents reveal that the Spanish disapproved of

Maya food and eating habits (Landa, in Tozzer 1941). As observed by Emery (1999: 78),

the maintenance of Late Postclassic dietary traditions at Lamanai in colonial times,

particularly animal utilization, reflects “a conscious return to traditional Maya foodways

and identity”.

Faunal and bone isotopic evidence may reflect general dietary stability in 16th

and

17th

century Lamanai, but observable changes in the types of exploited animal resources

also characterize the Historical period. At Lamanai, the introduction of bow and arrow

and fish netting technology in the Postclassic accompanied intensive exploitation of

276

freshwater resources into the colonial period (Emery 1999; Graham 1991). In particular,

fish and birds were intensively exploited in lieu of mammals.

Significantly, species shifts in animal exploitation reflect a level of socio-economic

and political upheaval associated with colonization, as well as the vulnerability of

reduced communities to inconsistent and unpredictable food production (Graham et al.

1989; Pendergast 1991b). Historical references to famines at Lamanai (J.F. Chuckiak,

pers. communication, 2004) fortify the precarious food situation at the site. Thus, while

the colonial Maya menu generally resembled the pre-contact diet, relative food

proportions (e.g., maize vs. meat) in Historical meals were probably more variable within

a season.

Based on hard tissue evidence of increased health disturbances during colonial times

(White 1986; White et al. 1994; Wright 1990) and the enamel strontium data, it is

postulated that poor colonial health may have affected Lamanai adults’ ability to produce

or procure nutritious foods for weanling infants. Due to the fluid nature of reduced

communities, agricultural production is often disrupted and unreliable (Graham et al.

1989). Conversely, diminished food sources and poor nutrition will lead to ill health. In

either case, it is a synergistic cycle that can result in exacerbation of the original

predicament.

Inconsistent maize production, in addition to ecological crop failure, seasonal

availability of wild resources and childhood illness are important factors that would lead

to changes in infant diet and the Sr/Ca composition of enamel. While pre-contact Maya

would have been subject to similar factors, the prevalence of Historical individuals with

fluctuating enamel Sr/Ca suggests that they were more vulnerable to dietary uncertainties,

277

and this is attributed to demographic instability, political economic factors and

epidemiological conditions.

The variable infant dietary pattern of colonial times may also reflect the impermanent

situation of northern Yucatec Maya refugees, who migrated to the southeastern periphery

to escape the greater Spanish domination of the northern Lowlands (see Chapter Two).

Their presence at Lamanai in colonial times resulted in a more heterogeneous population,

and it is possible that the enamel data identifies them.

In the end, whether motivated by child illness, dietary instability or political defiance,

many Historical Maya women at Lamanai delayed the supplementation of solid food to

their infants and breastfed longer than pre-contact mothers, potentially with detrimental

effect. Biologically, despite the overall benefits of extended breastfeeding, several

negative consequences can arise in both mothers and children if adequate nutrition is not

maintained. For optimal nutrition and growth, medical experts traditionally advise that

the introduction of solid foods should begin at approximately six months of age, when

breast milk quality, notably iron content, declines and infants require additional nutrients

to sustain growing energy requirements and general development (AAP 1980; Riordan

and Auerbach 1993; WHO 1981; Whitehead 1983, and many others). Indeed, a

significant increase in mean Sr/Ca between 0.5 and 0.75 years of age (6-9 months) for the

entire Lamanai sample (see Figure 7.1) suggests that solid food supplementation did

commence at this time.

Exclusive nursing for an extended period beyond six months of age can readily result

in malnourishment (Mata 1990). Specifically, breastfeeding for more than a year has

been negatively associated with growth and nutritional status (Asenso-Okyere 1996; Rao

278

and Kanade 1992). Sultan and Zuberi (2003) also attribute a late weaning age (i.e., mean

of 7 months) to be the most significant risk factor (predictor) in the development of iron

deficiency anemia in toddlers aged 1-2 years.

The negative association between prolonged breastfeeding and growth and nutritional

status is not consistent, however, due to differences in the control of variables such as

cultural and socioeconomic factors in clinical studies (see Buckley 2001). Other research

reflects a positive relationship between extended nursing past one year and infant growth,

as well as a decrease in malnutrition risk (Cousens et al. 1993; Prentice 1994; Taren and

Chen 1993). Importantly, mothers must balance the increased risk of parasitic infection

associated with food supplementation, with the need for increased nutrition for adequate

growth.

With changing attitudes, the American Academy of Pediatrics (AAP 1996) has

recommended breast milk consumption as the optimal infant diet for at least the first 12

months, “and thereafter for as long as mutually desired”. In Western societies

particularly, women have revived the practice of “Stone Age mothering” that is

advocated by La Leche League, whereby breast milk is always available to infants, who

nurse on demand, and can involve prolonged night nursing, co-sleeping and late weaning

(also see Hausman 2003; Menon et al. 2003). Fortunately, this is starting to provide

important western clinical data that can be systematically researched to assess the

physiological consequences of extended breastfeeding up to four years of age (e.g.,

Buckley 2001).

In truth, when nursing is extended, i.e., beyond two years of age, breast milk

consumption usually reflects a minimal (insignificant) dietary contribution.

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Contemporary mothers themselves recognize that breastfeeding after one year represents

a minor dietary supplement to total diet (Buckley 2001). Instead, the continuation of

nursing beyond two or three years of age primarily fulfils an emotional purpose (Buckley

2001). As Buckley (2001) found, long-term “comfort nursing” is a nurturing process that

promotes mother-child bonding and acts to soothe and pacify both children and mothers.

With extended nursing, mothers recognize that their children obtain essential nutrients

from foods other than breast milk (Buckley 2001).

Buckley (2001: 310) found that nursing children aged one to four years required an

average intake of 100-460 mL of breast milk per day to meet the RDA recommendations

for energy intake and nutrients that were lower in their diet compared to national surveys.

Long-term nursed children had complementary (non-breast milk) diets that met an

average of 77% of the RDA for energy intake and at least 70% of the RDA for protein,

vitamin C, thiamine, riboflavin, niacin, vitamin B6, phosphorous and magnesium

(Buckley 2001: Table 4). This compares to non-breastfed children aged 1-3 years who

had mean energy intakes that met 93-108% of the RDA, the standards of which generally

exceed most children’s physiologic requirements (Buckley 2001).

The mean weight of breastfed infants is also significantly lower than formula-fed

infants up to 18 months of age (Dewey et al. 1992). However, Buckley (2001) found that

although children who nursed after the first year had lower weight-for-age, length/height-

for-age and weight-for-length/height, their values fell within two standard deviations of

the median and were deemed indicative of normal growth. Thus, while there are slight

nutritional inadequacies among long-term nursed children, her data reflect the absence of

major nutritional deficiencies among such children. Buckley (2001) posits that breast

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milk probably compensates for the lower levels of nutrients found in children’s

supplementary foods, but further research is needed to assess the degree to which breast

milk contributes to the daily energy and nutrient intakes of children who breastfeed in

later years.

Maternally, lactating mothers experience short-term and long-term effects of

breastfeeding. The nutritional stress on mothers during lactation actually exceeds their

nutritional needs during pregnancy (Institute of Medicine 1991). Common short-term

physiological changes include increased energy expenditure; declining body fat

composition in the first six months of lactation, followed by increased body fat afterward;

ovulation suppression; and nutrient deficiencies (Picciano and Lonnerdal 1992).

Most significantly, the calcium requirement of nursing mothers increases to supply

nutritionally balanced breast milk. Adequate milk calcium concentration is maintained

by decreasing renal excretion of calcium and increasing bone calcium resorption (Cross

et al. 1995; DeSantiago-Soledad et al. 2002; Kent et al. 1990; Krebs et al. 1997; Laskey

et al. 1998; Sowers et al. 1993, 1995). Even in well-nourished mothers, particularly those

on high fiber (maize) diets (De Santiago et al. 2002), negative calcium balance can result,

with consequent reductions in bone mineral density (Cross et al. 1995; DeSantiago et al.

2002; Kalkwarf and Specker 1995; Krebs et al. 1997; Laskey et al. 1998; Sowers et al.

1993, among others). This long-term effect is particularly evident during menopause and

commonly affects the spine, femoral neck and trochanter (e.g., Gur et al. 2003).

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8.4 The Implications of Infant Weaning Behavior for Ancient Maya Society

As a patriarchal society, ancient Maya recognized gender distinctions favoring males

that were manifest in several ways. Socially, economically, and politically, males

dominated Maya society and these advantages can be recognized in human hard tissues

because of increased access to status foods and enhanced nutrition (White 1999; White et

al. 1993; Whittington and Reed 1997; Wright and White 1996; among others).

Like many women in patriarchal societies, Maya mothers deferred status foods to

husbands and male children as a result of long-standing “processes of enculturation that

link(ed) food, status and gender” (Ardren 2002: 73). In many such societies, the custom

to invest greater childcare on male infants can begin at birth (Saunders and Barrans 1999)

and often entails extended breastfeeding, or delayed weaning, in such children (see Fildes

1986; McKee 1984). In Europe, medieval writers and doctors specifically recommended

an extra 6-12 months of nursing for male infants (Fildes 1986).

The nature of Lamanai enamel Sr/Ca reflects this gender discrimination to an extent.

While not significantly different, the Postclassic male pattern appears slightly delayed

compared to female individuals (Figure 7.9). Specifically, males appear to receive breast

milk up to 0.25-0.5 years longer than female infants (or receive comparatively less solid

food supplementation than females), which is compensated by a subsequent acceleration

in food supplementation.

In fact, Postclassic female enamel strontium is slightly elevated compared to the

mean values of all Postclassic and Historical cohorts (Figure 7.4), possibly suggesting

their earlier food supplementation. While some female adults exhibit higher bone Sr/Ca

compared to males, which has been attributed to metabolic changes associated with

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pregnancy and lactation (see Chapter 4.4), such a distinction obviously cannot account

for the differences observed here in enamel formed during childhood. No evidence exists

to indicate that infant girls differ in strontium discrimination or hard tissue incorporation.

The disparity would appear to reflect differences in dietary supplementation (and

maternal childcare) of Lamanai boys versus girls.

Furthermore, possible gender distinctions in the rate of enamel development may

affect dietary reconstructions based on enamel Sr/Ca between males and females.

Several human and primate studies have found that female dental development is

advanced compared to males (Demirjian 1986; Demirjian and Levesque 1980;

Kuykendall 1996; Moorrees et al. 1963). While the difference is not large, i.e., in the

range of 2-3% (see review in Smith 1991), the difference in mean enamel Sr/Ca observed

between the sexes suggests that female food supplementation and weaning is even further

advanced compared to boys.

If one assumes that the relative mean Sr/Ca patterns reflect tangible differences in the

time required to attain comparable values, as “shifting” sample distributions illustrate

(Chapter Seven), then one can recognize important distinctions in the level of food

supplementation between cohorts. In this case, one can assess the physiological

consequences of a 3-6 month delay among Postclassic male infants, which is apparent

from the start of enamel sampling, i.e., 6 months of age, but which may have begun

earlier. At this early age, increased nursing of male infants compared to females, or less

solid food supplementation of males compared to females, may have entailed nutritional

consequences such as reduced growth rate and possible deficiencies (e.g., iron).

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However, subsequent accelerated food supplementation among males after two years

of age, which is evident as a steeper Sr/Ca slope (Figure 7.6), indicates that Postclassic

males may have recovered from the early delay in supplementation. Hard tissue evidence

supports this, with no gender differentiation in disease and undernutrition in Lamanai

adults (White 1986; Wright 1990). Rather than being nutritionally detrimental, it appears

that the expedited food supplementation of infant boys after a slightly longer intensive

nursing period, i.e., shorter transition period to total food reliance, compensates for the

early delay.

Postclassic females also reflect greater fluctuations in enamel Sr/Ca compared to the

number of males exhibiting the expected pattern of increasing strontium over time. This

suggests that female children may have been more susceptible to dietary inconsistency or

illness than boys and reflects the greater gender differentiation in the pre-contact period.

The gender distinction is less evident in Historical individuals. The general equality

that is reflected in Historical male vs. female enamel Sr/Ca (Figure 7.11a) indicates that

infants at this time shared a feeding pattern that was not significantly influenced by

gender. This is not unusual considering the egalitarian (yet subordinate) status of all

colonial Maya reduced under a Spanish system. The archaeological record at Lamanai,

particularly the nature of Maya interments, supports this shared social position (Graham

et al. 1989; Pendergast 1991b, 1993).

Yet, Historical females do have a slightly reduced mean Sr/Ca ratio at almost all age

intervals, indicating that there might have been some gender differences. In this case, it

is female children who are delayed, possibly by as much as one year, in attaining

comparable enamel Sr/Ca (food supplementation) as boys (see Figure 7.11b). Raw bone

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strontium abundance quantified by White and Schwarcz (1989: Table 6) support the

gender difference. Bone strontium averages 96.6 ppm (N=15; s.d.=12.7) for combined

Postclassic and Historical females, while males from the same period average 105.3 ppm

(N=14; s.d.=26.2) (White and Schwarcz 1989: Table 6).

At many Maya sites, skeletal and dental evidence portray girls and women as

disadvantaged members of society, with poorer health and reduced access to resources

(Ardren 2002; Saul and Saul 1997; Whittington 1991; Whittington and Reed 1997). At

Lamanai, this is manifest in bone chemistry as greater meat and seafood consumption

among males, particularly elite males, in the Classic period (White 1986; White and

Schwarcz 1989).

The findings are not consistent, however, as other evidence indicates general equality

between the sexes. For instance, macroscopic and microscopic enamel defects, which

reflect physiological disturbances (dietary or disease-related), are equally distributed

among the sexes in many Maya samples (e.g., Danforth 1997; Song 1997; Whittington

1992), including Lamanai (White 1986). Porotic hyperostosis prevalence at Lamanai

similarly reflects gender equality (White et al. 1994).

Other dietary reconstructions based on bone composition refute gendered distinctions

in food access (Gerry and Chesson 2000). It could be implied that male and female Maya

infants probably shared the same weaning process (Danforth et al. 1997; White et al.

1994), but the inconsistent data suggests that there is no pan-Maya blueprint for gendered

weaning behavior, with differences possibly related to regional or even site-specific

socio-political and economic factors that determine gender relations.

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Finally, the enamel strontium data reflects important distinctions between individuals

who died as children and those who survived to adulthood. Though not significantly, it

appears that Postclassic individuals who died in childhood may have been delayed in

obtaining comparable levels of solid food supplementation as surviving adults. Like

early supplementation, delayed supplementation later in infancy (i.e., after six months of

age, when children’s energy requirements increase) also has potentially detrimental

repercussions.

It is proposed that some Lamanai individuals who died as children may have been

“breast starved” (Orkney 1946), or exclusively breastfed for more than six months. This

can readily lead to malnutrition, particularly protein and iron deficiency, and may have

been a contributing factor to early mortality. In fact, growth faltering has been observed

as early as three months of age in exclusively breastfed (indigenous) infants in

Mesoamerica (Butte et al. 1992; Rivera and Ruel 1997).

Even in cases of extended nursing, breast milk’s anti-microbial and immunological

qualities are active and provide supplemental protection for growing children (Institute of

Medicine 1991). There is no clear consensus on the nature of breastfeeding and mortality

after the first year, however, with some research indicating continued safeguarding

against mortality up to three years of age (Briend et al. 1988), while others find no

protection associated with extended nursing in the second and third years of life

(Cantrelle and Leridon 1971). As discussed earlier, exclusion of solid foods from infants

can be attributed to several factors, mainly concerning cultural taboos about food

contamination and diet during illness.

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8.5 The Comparative Hard Tissue Strontium Data

As there is no comparative incremental Sr/Ca data for human enamel, results of this

investigation can only be assessed by analogy to bone chemistry findings. Table 8.3

outlines the results of paleodietary investigations and also includes mean Sr/Ca ratios

from a clinical study of human bones from the United Kingdom between 1960-1968

(Sillen and Kavanagh 1982: Table 4, adapted from United Kingdom Medical Research

Council, 1959-1970). Total enamel Sr/Ca derived from 86

Sr/43

Ca ratios in Section 7.2

can be compared to such research.

Results from Sillen and Smith (1984) represent the first paleodietary study to

associate bone strontium with infant diet and weaning. As their report provides only

graphic distribution of Sr/Ca ratios (Figure 3), one refers to Katzenberg and colleagues’

(1996: Table 2) estimate of the values. Similarly, their organization of the results from

Grupe (1986) and Huhne-Osterloh and Grupe (1989) (see Katzenberg et al. 1996: Table

2) is referred to in the following table (Table 8.3).

Other bone strontium data in this comparison include estimates from Farnum and

Benfer’s (1995: Figure 4) report on ancient Peruvian infant bones and, most recently,

Mays’ (2003) analysis of Medieval British bones (estimates from Figure 1). Individual

tables in Chapter Five outline the supporting details of such calculations (when

available), such as sample numbers (N), standard deviation and range.

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Table 8.3 Comparative age-related mean Sr/Ca (x 10-3

) values from various clinical and paleodietary investigations

Age

(in years)

United Kingdom

Medical Research

Council (1959-1970)

Sillen and

Smith 1984

Grupe 1986;

Huhne-Osterloh

& Grupe 1989

Farnum and

Benfer 1995

Mays 2003

Song 2004

Birth

0.22

1.50

0.52

0.5 0.22 1.75 0.58 0.87 0.71

1 0.29 2.25 0.54 0.73

2 0.27 2.50 0.72 0.89 0.76

3 0.23 2.25 0.84

4 0.30 0.63 0.85 0.97

5 0.29 1.07

6 0.32 0.84 1.13

8 0.27 1.60 0.75

14 0.27 0.51 0.79

Adult 0.27 1.80 0.53 0.69

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As the table indicates, there is considerable variation in the total Sr/Ca abundance of

human hard tissues, which is not unexpected considering the geographic differences.

Notably, Sillen and Smith’s (1984) mean Sr/Ca values of ancient Arab bones is higher

than any other known data, with a range of approximately 1.5 x 10-3

(0.0015) to 3.0 x 10-3

(0.003). The authors do not specify whether these ratios are the result of relatively high

Sr values, or relatively low Ca abundance. Mays’ (2003) data is most comparable to this

study, ranging from approximately 0.50 x 10-3

(0.0005) to 1.05 x 10-3

(0.00105), or a

mean ratio of 0.855 x 10-3

(0.000855) among juveniles and 0.692 x 10-3

(0.000692)

among adults.

Farnum and Benfer (1995) have also examined Sr content in ancient Peruvian bones

to identify weaning, but in their opinion, the Sr/Ca values were too high not to rule out

diagenetic alteration. In their scatter plot of Sr abundance, the peak value, observed for

bones at one year of age, is approximately 540 ppm, or 0.54 x 10-3

(Farnum and Benfer

1995: Figure 4). However, placing their data in the context of other studies and clinical

data (Table 8.3) indicates that this mean ratio is actually within the normal range of

human findings, and is comparable to values in this analysis.

Besides absolute Sr/Ca values, two main differences can be recognized between the

Lamanai results and other studies, which can be attributed to the nature of sample

collection and analytical technique. Though not significantly, 1) the total mean Sr/Ca

increase in the Postclassic and Historical Lamanai samples is pronounced compared to

other studies, and 2) the Lamanai patterns also exhibit more variation that does not

necessarily adhere to the expected model of positive increase followed by decline and

stabilization.

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Sr/Ca change over developmental time in Lamanai individuals involves a roughly

twofold increase in values. The mean increase in Sr/Ca is 1.807 among Postclassic Maya

and 1.873 in Historical Maya at Lamanai, which occurs over an extended period between

0.5 and 5.5 years of age (Table 7.15).

In comparison, Sillen and Smith (1983, 1984) found that Sr/Ca increases by a factor

of approximately 1.67 between birth and two years of age (see Katzenberg et al. 1996:

Table 2). Sr/Ca values of Medieval Arab bones gradually increase after birth, with

individuals aged 1.5 to 3.5 years having the highest values for the entire population,

which peaks at around 2 years of age (Sillen and Smith 1984). This is consistent with

ethnographic data on traditional Palestinian Arab communities, whose children consumed

breast milk until two to three years of age (Grinquist 1947). Afterward, with increased

gastrointestinal discrimination of strontium, Sr/Ca values decline to levels that persist

throughout adulthood.

Grupe (1986) and Huhne-Osterloh and Grupe (1989) also examined strontium

concentration in ancient German bones to estimate weaning age. They found the highest

Sr/Ca ratios in children aged six months to two years, the period they attribute to dietary

supplementation and weaning. In this case, Sr/Ca increased by a factor of 1.24 (see

Katzenberg et al. 1996: Table 2). Like Sillen and Smith (1984), bone strontium levels

declined in subsequent age groups.

Finally, Mays (2003) found that bone Sr/Ca increased most significantly between one

and two years of age in a Medieval skeletal sample, the period of significant food

supplementation. A steady decline in Sr/Ca from about two to eight years of age, when

values then resemble adults, indicates that most children in this sample were fully weaned

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by two. The overall rate of increase between exclusive breastfeeding and weaning is not

explicitly stated, but graphical data suggest that infant bone Sr/Ca rises by a factor less

than 1.25 (Mays 2003: Figure 1). In this instance, Mays (2003) determined that the

transition from exclusive breastfeeding to an adult diet involved an increase in dietary

Sr/Ca by a factor of three to four.

In Mays’ (2002) study, bone strontium composition accords well with nitrogen

isotope results and Medieval documentation about infant diet. However, importantly, it

should be realized that in all cases, calculation of the dietary Sr/Ca based on Rivera and

Harley (1965) will indicate a significant rise in Sr/Ca at two years of age due to their

significantly reduced OR value at that age. Even in cases where hard tissue Sr/Ca is

stable or slightly diminishing between birth and two years of age (and older), enhanced

strontium discrimination at two years of age (more than three times) will return a

substantially higher dietary Sr/Ca value at that age. This pattern more correctly reflects

the increased ability to discriminate against strontium in more mature infant guts.

This fact reinforces the necessity for supporting contextual data in paleodietary and

paleonutritional investigations. In the reconstruction of ancient weaning based on hard

tissue chemistry, ethnographic, historical and archaeological inferences are imperative.

The hard tissue and dietary Sr/Ca data of Mays’ (2003) and Sillen and Smith’s (1984)

studies are validated by historical documentation, but here, in light of ethnographic

observations, the dietary Sr/Ca derived from enamel strontium must be scrutinized.

On one hand, inferred dietary Sr/Ca indicates that Lamanai Maya children

significantly increased their solid food intake at approximately two years of age. Stable

isotopic composition (δ15

N and δ13

C) of ancient Maya teeth from Kaminaljuyu support

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this, with nitrogen data indicating that proteins from milk became less important in infant

diet by two years of age, when milk proteins were largely replaced by solid food proteins

(Wright and Schwarcz 1998, 1999). According to Wright and Schwarcz (1998, 1999),

Maya infants were nursed for at least one year or longer. While all children began

consuming significant quantities of solid food before two years of age, many children

were substantially supplemented by one year of age.

At the same time, enamel δ18

O suggests that children continued to rely on breast milk

for many years afterward, i.e., up to five or six years of age. Two different nursing

“strategies” are identified from the dental nitrogen and oxygen isotopic data: 1) many

children who imbibed breast milk up to five years, primarily as a water source; and 2)

few children who relied on breast milk to provide nutrients beyond one year of age

(Wright and Schwarcz 1999). Unfortunately, historical documentation does not reveal

when Maya infants were significantly supplemented with food, and contemporary

evidence in this regard is also lacking (Wright and Schwarcz 1998: 12).

Considering the various nutritional, physiological and social data, greater food

supplementation at two years of age can be associated with a combination of factors: 1)

growing developmental needs of children; 2) complete eruption of the deciduous

dentition, which is perceived to accommodate greater solid food intake; 3) better

developed digestive systems; and 4) increased child interaction with a wider social

environment.

On the other hand, as also found by Wright and Schwarcz (1998, 1999), it is likely

that many Maya infants were significantly supplemented earlier than two years of age,

but this is not evident in the Lamanai dietary Sr/Ca values due to the reduced OR factor

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at two years (which will always indicate a substantial increase at this age). As well,

supplementation with substantial solid food after two years of age will not be visible in

the dietary Sr/Ca values due to the stabilization of hard tissue OR after that age. Enamel

Sr/Ca values at age three and older would have to be higher than two-year-old values by

an order of magnitude to reflect a significant difference with dietary Sr/Ca at two years of

age. This is not evident in the enamel strontium data presented here.

Nevertheless, based on the supporting data, it can be postulated that most Lamanai

children probably started consuming significant quantities of solid food at around two

years of age, with weaning taking place several years later. But while enamel strontium

can be used to infer the age of weaning, the nature of this investigation cannot clarify the

relative proportion of breast milk and solid food in later infancy.

In this study, among most Lamanai individuals, enamel Sr/Ca reaches its peak

between 4.5-5 years of age. Specifically, Postclassic Maya display peak values followed

by stabilization between the ages of 3.75-5 years, while the highest Historical Maya

values range from 3.5-5.25 years of age. In the entire sample, the time it takes to reach

peak Sr/Ca ranges from 2.75 to 4.25 years (see Section 7.3). In each distribution, a

subsequent drop in Sr/Ca reflects the more efficient discrimination of Sr by mature

digestive systems. These findings are significantly later than those found by Sillen and

Smith (1984), Huhne-Osterloh and Grupe (1989) and Mays (2003), which all attribute

peak bone Sr/Ca values to around two years of age.

However, it is also known that strontium levels are the most varied among children,

particularly between the ages of 4 and 13 (Lambert et al. 1979; Sillen and Kavanagh

1982). In fact, Rivera and Harley (1965) found that Sr/Ca values only reduced to

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comparable adult levels by 8-10 years of age, when the digestive system is fully mature

and efficient at discriminating against strontium. Adolescence is also characterized by

high Sr values due to increased metabolic activity (Lambert et al. 1979; Loutit 1967). In

general, permanent enamel strontium is highly variable, with values as low as 13 ppm to

1400 ppm in teeth from dissimilar geographic regions and time periods (Chapter Four).

The comparison of bone Sr reference data to this dental study might account for some

differences in Sr/Ca, but bone Sr concentrations generally resemble enamel values: bone

Sr averages between 150-250 ppm (Aufderheide 1989), while enamel Sr commonly

ranges between 100-200 ppm (Brudevold & Steadman 1956). Nonetheless, in the event

that bone values are derived from diagenetically altered tissues, which is not uncommon

for bone Sr composition, the use of different hard tissues may be a significant factor.

Imprecise “ageing” of bone remains due to continuous tissue regeneration may also

account for some differences.

Two additional factors are also considered. Firstly, the late age of Sr/Ca stabilization

may simply reflect the extended breastfeeding behavior of ancient Maya children. The

populations examined by Sillen and Smith (1984), Huhne-Osterloh and Grupe (1989) and

Mays (2003) are known to have nursed for considerably shorter periods, including earlier

supplementation with animal milk in the Medieval British sample (Mays 2003). As

observed by Schroeder and colleagues (1972), children and adults from cultures that

consume animal milk after childhood tend to have reduced hard tissue Sr/Ca due to

higher calcium intake.

Second, instrumentation factors such as sample buildup and associated memory

effects in the ICP, or elemental fractionation over time, might account for a continued

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rise in Sr/Ca over time, resulting in peak values at the end of the ablation sampling. The

ablation of calcified tissues can lead to significant intrainstrument buildup of calcium and

instrument drift (Outridge et al. 1995). But in such cases, particularly with carbonate-

based samples, calcium is accumulating in comparable abundance, so that any ratio, e.g.,

Sr/Ca, should remain indicative of true composition. Furthermore, in this study, as

terminal element values of an ablation correspond very well with initial values of the

subsequent ablation (facilitating “pasting” of multiple ablations to create one complete

graph), it does not appear that calcium accumulation is significant. In total, the

correspondence of enamel strontium patterns between ablations within an individual

tooth and the variability of enamel strontium patterns suggests that the increasing Sr/Ca

behavior observed in most Lamanai teeth are real and reflective of dietary

supplementation.

8.6 Recommendations for Future Research

This study represents the first intensive reconstruction of ancient infant diet using

LA-ICP-MS analysis of human enamel. As a result, there is a lack of comparable data,

but it is anticipated that these challenges will be resolved with additional research.

Like other avenues of bioarchaeological research, standardization of analytical

methodology would be invaluable, particularly in: 1) tooth sample preparation, including

the use of macroscopic or histological landmarks for tooth sectioning (e.g., to capture

consistent areas of enamel according to developmental age); 2) LA-ICP-MS operating

parameters; 3) data organization (e.g., software); and 4) use of specific isotopes for

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element ratioing. Improvements in quantification, such as matrix-independent solid

reference materials, would also facilitate data comparisons.

Gunther and colleagues (2000: 13) predict that future LA-ICP-MS instrumentation

will be simplified in set-up and operation, with increased automation with sample

changers and data reduction. Continued investigation into laser wavelength, transport

efficiency and element fractionation (Gunther et al. 2000; Roy and Neufeld 2004) will

surely enhance the technology and fine-tune its application to bioarchaeological research.

Beyond this, as undertaken by Haverkort (2001), applying LA-ICP-MS to the hard

tissues of individuals with known dietary history will further evaluate: 1) the suitability of

the technology to paleochemistry and paleonutrition; 2) the complex nature of element

relationships between dietary components and the effect on total element intake; and

most fundamentally, 3) the relationship between dietary intake and enamel incorporation.

For this specific investigation into the nature of hard tissue strontium and solid food

supplementation, further quantification of strontium would be a fruitful avenue of

continued research. Less elements, i.e., only strontium and calcium, might be quantified

at a slower scan speed, which would reduce the “memory effect” common with LA-ICP-

MS, when ablated material is mixed with material from subsequent laser pulses due to the

delay during sample transport from the ablation chamber to the ICP (see Haverkort

2001). This would improve spatial resolution and sample quantification, as well as

reduce instrumentation error.

LA-ICP-MS analysis of other teeth could also contribute important supporting data.

In particular, since the earliest canine enamel (developing at birth) is not sampled due to

its interior (“hidden”) position, analysis of deciduous enamel developing before and at

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birth, e.g., deciduous canines and molars, could provide an unequivocal non-food

supplemented Sr/Ca baseline from which permanent canine enamel could be compared.

However, in this case, analysis of deciduous enamel would be limited to individuals who

died as children and who retain complete crowns of such deciduous teeth, in addition to

secondary canines, i.e., those who died between approximately six and ten years of age.

To verify the findings in this research, i.e., the association of permanent canine

enamel Sr/Ca with infant diet and weaning, isotopic analysis would be a worthwhile

future endeavor. In this case, the same Lamanai canines could undergo additional

microsampling to quantify carbon (13

C), nitrogen (15

N) and oxygen (18

O) isotopic

composition. As described in Chapter Five, such isotopes can be used to infer the

introduction of non-breast milk water (oxygen) and maize foods (carbon), as well as the

cessation of nursing (nitrogen).

Drawing from this study’s dataset, other elements quantified by ICP-MS could also

be analyzed. To elucidate the weaning process, zinc may be another valuable element

that can be associated with changes in relative breast milk and solid food consumption.

Breast milk is known to be a good source of zinc (Institute of Medicine 1991; Lonnerdal

et al. 1981), but during the course of lactation, its zinc levels have been observed to

steadily decrease (Karra et al. 1988). Similarly, Farnum and Benfer (1995) observed

diminishing Zn levels in the bones of young children, but they could not differentiate

whether the low levels were due to changes in infant diet and weaning or other dietary

and health stresses (e.g., protein deficiency).

Like hard tissue elemental studies in general, which dwindled in light of diagenesis

research and better understanding of the preservation of bone elements, zinc has not been

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investigated in the context of weaning studies since. However, in the context of dental

enamel research, it is possible that re-examination of zinc incorporation during infancy

and weaning, and use of microsampling techniques to provide continuous data at each

stage of the process, may provide useful comparative data for the strontium evidence.

Finally, beyond weaning, strontium isotope analysis would be an important extension

of this investigation to assess the nature of population heterogeneity at Lamanai.

Strontium isotope ratios (87

Sr/86

Sr) have been examined to identify the childhood origins

of individuals and groups, as well as the nature of group migrations among

archaeological samples (e.g., Budd et al. 1996, 1997; Goodman et al. 1999; Grupe et al.

1997; Gulson et al. 1997; Price et al. 1994; Prohaska et al. 2002; Sealy et al. 1995). It is

based on the premise that distinct ratios of the two isotopes reflect different geological

environments, most notably local water, soil and food.

This is an area of research with significant implications for population dynamics in

the Maya area as well, and particularly for Lamanai, which is known to have been a

frontier mission. Strontium isotope levels could shed light on questions of origin, and

provide a clearer picture of population movements incurred by Spanish reducciones.

Importantly, identification of immigrants in the Maya colonial cemetery at Lamanai

might explain the degree of variation in enamel Sr/Ca from this cohort. Colonial

Lamanai individuals raised elsewhere as children would have had varying experiences

with disease, famine, diet changes, violence, psychological trauma, and the stress of

migration. Thus, for instance, one might be able to associate a highly variable/fluctuating

enamel Sr/Ca pattern with individuals originating from regions that suffered the most

under colonialism.

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CHAPTER 9

CONCLUDING REMARKS

As animals, what we eat determines the course of our biological and social evolution.

This realization has fueled the immense growth in paleonutritional studies that seek to

reconstruct subsistence from hard tissue chemistry. Advances in analytical chemistry

have greatly aided in the pursuit.

From this investigation, LA-ICP-MS results of enamel composition suggest that

strontium patterns do reflect changes in diet attributed to solid food supplementation,

waning breast milk intake and eventual weaning. This process begins before a Lamanai

child’s first birthday and ends three to four years later.

As illustrated by this study, the reconstruction of ancient diet and feeding behavior

must be an essentially holistic, anthropological, endeavor. Since the interactions

between food chemistry, processing techniques, human metabolism, health, nutrition and

hard tissue incorporation are complex and incompletely understood, diet must be

reconstructed within the context of diverse data. A critical biocultural approach accounts

for the interrelatedness of social and physical environments and it is a research paradigm

that clearly recognizes the diverse conditions that shape the health of society’s most

vulnerable members.

In this way, enamel development and diet-related chemical composition are viewed as

sensitive indicators of total environmental quality. Variations in enamel Sr/Ca pattern

within and between individuals reflect this sensitivity.

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Teeth are proven to be the ideal human tissue for paleodietary reconstruction based

on chemical composition. Circumventing the main challenges of bone chemical analysis,

i.e., mineral preservation and diagenetic alteration, this dental study represents a return to

hard tissue element analysis. The kymographic nature of teeth, at a known rate of

development, is an additional advantage and it is perhaps its most unique feature. It

means that enamel represents a detailed chronicle of important milestones in early life

history. In this case, it has allowed observations of the dietary transition to weaning and

has provided an enriched understanding of indigenous health and nutrition.

For Lamanai, archaeological, osteological, ethnohistorical, ethnobotanical,

zooarchaeological and bone chemical evidence provide substantial inferences for the

nature of infant diet and health before and after contact. Invaluable contextual

information includes details of childcare, maternal health, female household and non-

domestic roles, and gender disparities. Altogether, the evidence elucidates the five

archaeological questions that were posed at the start of this analysis:

1) Are there temporal distinctions in breastfeeding and dietary supplementation between

pre-colonial and historical periods?

The data suggests that there are recognizable distinctions in subsistence pattern

between Postclassic and Historical Lamanai children. The primary differences

concern a) age of initial food supplementation, which is delayed in colonial children

compared to pre-contact children; and b) dietary inconsistency, which is more

prevalent in colonial children, who exhibit more fluctuations in alternating breast

milk/solid food intake.

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2) Did Spanish control of economic activities, i.e., demands for agricultural products

and human labor, affect household patterns and childhood nutrition?

It is likely that Spanish demands for female-produced tribute products affected

mothers’ abilities to provide consistent solid food supplementation. However, as

tribute production was amenable to household settings, mothers were able to maintain

intensive childcare practices such as extended breastfeeding (see #3).

3) Did this demand for increased labor result in changes in weanling diet or duration?

The Sr/Ca evidence suggests that colonial period children consumed more breast milk

for longer periods than prehistoric children, i.e., they were weaned at a later age.

Maize gruel continues to comprise the bulk of weanling diet, but as in Lamanai

adults, the minor meat component of colonial children’s diet (when available)

probably shifted from land mammals to lagoon fish and birds.

4) Is the heterogeneous nature of the colonial mission population, including Maya

“refugees” from other areas, reflected in childhood diet and weaning patterns?

While identification of such sub-cohorts is not possible in this study, the extent of

individuals with variable Sr/Ca patterns in the colonial period may indeed reflect the

varied dietary patterns of the heterogeneous mission population. Fluctuating breast

milk and solid food intake of colonial children may also mirror the transitory nature

of colonial Maya refugees who settled at Lamanai, after fleeing from northern regions

(Yucatan) and epidemic disease. Dietary inconsistency would be an expected

outcome of their ecological, domestic and socioeconomic instability.

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5) Are there distinctions in weaning age, duration or diet that could be related to

socioeconomic status or gender?

A socioeconomic distinction is recognized between temporal cohorts at Lamanai,

with Postclassic Maya having greater access to resources (including social power),

than Historical individuals. This is manifest as differences in enamel strontium and

diet that are outlined in #1 above, i.e., reduced Sr/Ca values (delayed supplementation

and weaning) in the disadvantaged colonial cohort. With gender, distinctions are only

observed in the Postclassic sample, when males appear to be slightly delayed in initial

food supplementation compared to females, reflecting greater maternal investment in

boys. This gender-based childcare may have had developmental consequences for

later health and survival, but it appears that the delay in boys was brief and was

subsequently compensated by a faster rate of food supplementation. Hard tissue

evidence of health, such as bone and dental pathology, portrays gender equality in the

health and survival of Lamanai males and females.

Methodologically, laser ablation sampling combined with ICP-MS is proven to be a

highly sensitive method of quantifying hard tissue elements across developmental age. It

enables the most detailed hard tissue reconstruction of dietary fluctuations over time.

Most significantly, it indicates that the weaning process is more variable and complex

than previously recognized by other methods.

Recognition of fluctuating Sr/Ca values over an extended developmental period

highlights the microsampling advantages of LA-ICP-MS. While other studies can

compare element values between cohorts of one to two years (e.g., Grupe 1986; Huhne-

Osterloh and Grupe 1989; Mays 2003; Sillen and Smith 1984), these results reflect a

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level of intra-tooth variation and complexity that is not captured by macrosampling

techniques.

For bioarchaeological purposes, LA-ICP-MS offers a method of sampling that

broadens the questions that can be asked of human remains. For example, laser

microsampling can disclose greater variation in hard tissue composition across 1)

different tissues such as enamel and dentin (Haverkort 2003; Kang 2004); 2) different

teeth of comparable developmental age (Haverkort 2003); 3) pre-natal vs. post-natal

deciduous enamel (Goodman et al. 2003); 4) normal vs. defective enamel (enamel

hypoplasias or Wilson bands); and 5) surface vs. interior enamel or bone (for pollution

exposure and diagenetic diagnoses) (Budd et al., 1998; Cox et al. 1996; Montgomery et

al. 1998). Importantly, these investigations will enhance the understanding of childhood

nutrition and the nature of hard tissue incorporation under healthy, as well as less than

ideal, conditions.

As Outridge and colleagues (1995: 167) have stated:

LA-ICP-MS and other microprobe techniques are thus revealing that the

heterogeneity of metal distribution at microspatial scales is no less of a sampling

design problem than for macroscale entities such as forests, oceans, etc., and entails

similar types of statistical considerations, data management, and visual

representation.

Indeed, the data in this study have proven to be amenable to the same analytical

procedures as macrosampling techniques. While daunting at first, the ability to quantify

element ions at a micro scale provides a large reservoir of data that can be managed (i.e.,

reduced) in countless ways to suit the research question.

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An important consequence of this study concerns the nutritional relevance of the

existing definition of weaning, i.e., the cessation of breast milk intake. Previously, as

noted by Stuart-Macadam (1995: 82), studies of ancient weaning were limited by a lack

of “contemporary longitudinal data on infants who have been breastfed in the ‘ancient

pattern’, that is, for longer than one year and with gradual supplementation of additional

foods.” This situation is changing, however, as women in both western and non-western

societies increasingly adopt the “traditional” pattern of long-term breastfeeding.

Buckley’s (2001) report on such mothers highlights the potential clinical data that

will clarify the ancient pattern. From her observations, it appears that breastfeeding after

the second year represents an insignificant nutritional contribution. Its primary role

thereafter is for emotional bonding and mother-child socialization. In ancient

populations, breast milk may also represent an important source of water (see Wright and

Schwarcz 1998), but its nutritional role is minor after the first year.

For all intents and purposes, children nursing beyond two years of age should be

considered “weaned” at approximately two years, when nursing tends to diminish

significantly. In fact, this is the age when many ancient and contemporary children stop

breastfeeding. In societies that advocate nursing for up to four or five years, like the

Maya, it is nutritionally inconsequential to stress a late weaning age because, by then,

children have already been primarily dependent on an adult diet for a few years.

Furthermore, attributing a late weaning age of four to five years to ancient populations

like the Maya is not a novel concept. Ethnographic accounts already affirm this.

Based on this study, it is perhaps more meaningful to track the age of significant food

supplementation and dietary adaptations to external stress, rather than the age of breast

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milk cessation. In children breastfed for many years, health status and survival appear to

be better associated with the age of initial food consumption. Fortunately, enamel Sr/Ca

reflects the supplementation of solid food more confidently than the end of nursing

(weaning), and the patterns observed here have enriched the understanding of ancient

infant subsistence. Most importantly, the detailed and age-specific data provided by LA-

ICP-MS analysis of enamel documents a complex process leading to weaning. It

indicates that the process is highly sensitive to many external influences, which are

ultimately tied to interrelated ecological, political and economic factors.

In sum, the present research represents an evolution of the application of analytical

chemistry to paleodietary reconstruction. Several factors make this study exciting: 1) it

utilizes dental enamel, which is the least susceptible to post-mortem deterioration, and

thus, is more accurately reflective of intake and incorporation; 2) examination of

sequentially calcified, inert, dental tissue provides an indelible, detailed, history of intake

and nutritional status that can be captured by the localized sampling capabilities of laser

ablation; 3) employing LA-ICP-MS, it asks new, nutritional, questions of the dental

tissue analyzed by such technology. Sampling of permanent canine enamel, in particular,

allows reconstruction of dietary intake for the entire weaning process, which is a critical

period of childhood; 4) it applies minimally invasive microsampling technology to

multielement analysis that preserves the integrity of ancient remains; and 5) the Lamanai

sample presents a unique window into the dynamic processes that occurred at the

crossroads of Maya-Spanish contact. Above all, assessing the nature of infant diet by

LA-ICP-MS has provided invaluable inferences for the colonial consequences to Maya

childhood health and nutrition, an area that has been inadequately explored.

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APPENDIX A

DENTAL HEALTH OF LAMANAI CANINES

This chapter includes macroscopic data for all canines used in this analysis. While

the sampling of only one tooth per individual precludes conclusions on dental health, raw

observations are provided as “osteobiographic” information for each individual. Such

reference data (e.g., defect measurements) might assist future research on dental defects

and enamel timing. For additional dental data, one is referred to more complete analyses

done by White (1986) on whole dentitions of Lamanai individuals.

A.1 Dental Attrition, Caries and Calculus

All sixty permanent canines used in this analysis were assessed for general indicators

of age and dental health (see Table A.3). This entailed the extent of dental attrition,

caries, calculus deposition and macroscopic enamel defects (hypoplasia and

hypocalcification).

Dental attrition was assessed based on a comparative scale, with teeth being judged as

complete (no dental wear) (“0”), slight (“1”), moderate (“2”), moderate-heavy (“3”) and

severe (“4”) in wear. Slight attrition was comparable to Brothwell's (1981: Fig. 3.9)

Stages 1 to 3. Moderately worn teeth had some cuspal enamel missing (up to half), with

some inner dentine exposed, and followed Brothwell's (1981: Fig. 3.9) stages 3+ and 4.

Moderate-heavy wear was characterized as those teeth with almost all cuspal enamel

absent and dentine exposed (with about half the complete crown height) (see Brothwell

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1981: Fig. 3.9, stages 4+ and 5), while severely worn teeth were those with almost the

entire crown attritioned, sometimes down to the level of the root (see Brothwell 1981:

Fig. 3.9, stages 5+ to 6).

The canines were measured for complete crown height with sharpened electronic

calipers calibrated to 0.01 mm. Average unworn crown heights, specific to the Lamanai

population, are required for estimating the timing of enamel defects (see Table A.1

below). Crown heights of slightly worn teeth were also recorded to assess the degree of

missing enamel and the developmental period not recorded by such teeth (and not

sampled by laser ablation). Due to the requirement for intact, or mostly complete, teeth

for this study, samples with more than moderate-heavy wear were excluded. Obviously,

this biases the sample toward younger adults and children older than 5-6 years of age (the

age of permanent canine crown completion).

Carious lesions represent the progressive destruction of oral hard tissues by bacterial

activity and are assessed based on the number of carious lesions per tooth, as well as

lesion dimensions and tooth location. In ancient Maya samples, carious lesions

commonly afflict adult dentitions due to a high carbohydrate (maize) diet. Due to the

broad, fissured, surface of multi-cuspal teeth, premolars and molars will be the most

frequent site of carious activity. Conversely, single cusp teeth such as incisors and

canines are more rarely affected. Indeed, in this case, none of the utilized Lamanai

canines exhibit evidence of caries. Other reasons for this include the lack of older adults,

who tend to have more carious teeth, as well as the small sample size.

Finally, calculus deposits, or mineralized bacterial plaque containing calcium and

food debris, were rated following Brothwell (1981: Fig. 6.14b), with gradients of none

307

(0), slight (1), moderate (2), heavy (3) and very heavy (4). Generally, extensive calculus

deposits characterize adult dentitions, particularly older individuals. In the Maya area, a

high starchy maize diet means that calculus deposits often obscure the cervical margin

(crown base) of teeth. However, for this study, teeth with heavy or very heavy levels of

calculus were not included, either because of their permanent fixture on enamel surfaces,

and/or their association with heavily attritioned teeth. Canines used in this study are

either absent of calculus or have slight deposits.

A.2 Developmental Defects of Enamel

Macroscopic developmental defects of enamel are one of the most common

pathologies observed in archaeological populations and they include enamel hypoplasia

and enamel hypocalcification. Many researchers have examined enamel hypoplasia to

assess the health status of prehistoric and contemporary populations, particularly during

the weaning period, when the secondary dentition can be affected (see Chapter 5.4).

As a general term, enamel hypoplasia refers to all defects in enamel thickness, and is

thus, a quantitative defect. The enamel is usually deficient in quantity, but it may be fully

mineralized (Beynon 1986). On the other hand, hypocalcifications are simply areas of

opaque or discolored enamel that are smooth and normal in enamel thickness, except in

cases when they are combined with hypoplasia (FDI 1982). They are thought to be the

result of less severe stress, when compared to hypoplastic pits and bands (Blakey 1981).

Despite being the hardest substance in the body, with a rank of 3 on the Moh’s scale,

as well as the densest calcified tissue (about 3gm/cc) (Weatherell et al. 1967), enamel can

be subject to disturbances during its formation that alter its morphology and the physical

308

appearance of the crown. Enamel hypoplasia is the end result of disruptions in the

secretory/matrix formation phase of amelogenesis (Guita 1984; Shafer et al. 1983;

Yaeger 1980). Defective enamel can appear as 1) shallow or deep pits, or rows of pits,

arranged horizontally in a linear fashion across the tooth surface, or generally distributed

over the enamel surface; 2) shallow or deep, wide or narrow grooves or bands; or 3) as

regions of entirely missing enamel over small or large areas of dentine (FDI 1982: 160).

Three distinct factors contribute to the epidemiology of enamel defects. They include

hereditary, traumatic and systemic conditions. Generally, with archaeological samples,

the principal cause of enamel hypoplasia will be systemic factors (Goodman and Rose

1990; Goodman et al. 1984; Rose et al. 1985). Such defects are likely to be found on a

variety of teeth developing at the time of the stress, and their location on the crown

reflects the relative completeness of the enamel at the time of the disruption (Goodman et

al. 1980; Sarnat and Schour 1941; Pindborg 1982; Yaeger 1980).

Systemic conditions which can result in disturbed enamel formation include

malnutrition, infectious disease, exanthematous fevers, hypovitaminosis A, C and D,

hormone imbalance, fluorosis, neonatal tetany, hemolytic disease and prematurity, among

many others (Cutress and Suckling 1982; Beynon 1986; Blakey 1981; Moller 1982;

Newton et al. 1984; Purvis et al. 1973; Sweeney and Guzman 1966; Sweeney et al. 1969;

TenCate 1980).

Importantly, macroscopic enamel defects are relatively sensitive to growth

disturbances, and are nonspecific indicators of stress (Nikiforuk and Fraser 1981). It

should also be stressed that enamel hypoplasias indicate periods of stress that were

obviously followed by renewed enamel formation and recovery, representing an

309

individual’s survival of the stress. Populations experiencing severe, chronic malnutrition

and/or infections may not show any enamel defects due to a lack of recovery.

A.3 Scoring of Enamel Defects

Bioarchaeologists, dental anthropologists and dentists usually refer to either the

Federation Dentaire Internationale system (FDI 1982) or the Standards for Data

Collection from Human Skeletal Remains (Buikstra and Ubelaker 1994: Attachment 18a,

b) for recording developmental defects of enamel. These standards outline scoring

procedures for hypoplasias, opacities, combinations of both, and discolored enamel

(hypocalcifications).

In this study, hypocalcifications are described according to color and crown

distribution. Enamel discoloration, whether due to intrinsic or extrinsic factors, was

commonly found in the cervical region, i.e., accompanying calculus buildup. Calculus

staining therefore left the cause of enamel pigmentation in question, and the exact nature

of some discolorations cannot be identified. In truth, hypocalcifications are often not

scored in dental analyses as they frequently resemble extrinsic staining from either pre-

mortem (calculus), or post-mortem factors, such as the soil in the burial environment.

For measurements of enamel hypoplasia, the same sharpened electronic caliper was

utilized. The enamel defect was measured from the cemento-enamel junction to the

middle of the defect, if it was narrow, and to the superior and inferior borders if it was

broad. Thus, the entire period of defective enamel formation was recorded. At all stages,

enamel surfaces were visually examined under regular incandescent lighting, often

enhanced with natural light, and viewed with the unaided eye. Instances where defect

310

severity was questionable also involved the use of a hand-held magnifying glass.

However, consistent with Goodman and Rose (1990), if the defect could not be detected

without magnification, it was considered absent.

The present analysis varies slightly from the abovementioned standards (Buikstra and

Ubelaker 1994; FDI 1982), but it is closely comparable in the types of metric and

descriptive data that are outlined (if not more extensive in the recognition of defect

variations). Each tooth was assessed as descriptively as possible, making particular note

of the nature of defect types (shallow lines, grooves, bands, pits, patches of missing

enamel), location, color distinctions, and their measurements.

Figure A.1 Standards of enamel hypoplasia severity

(illustration of the labial surface of incisors)

According to Figure A.1, which follows the scoring of defects for Altun Ha (Song

1997), teeth are divided into two main categories, depending on defect width, or duration

of stress episode. “A” defects are narrow, or shorter in duration, and range from shallow

(1) to deep (3). “B” defects are broad, representing chronic stress, and are similarly

311

divided by depth (1-shallow to 3-deep). These degrees of defect depth (1, 2, 3) are

specified in Table A.3 (see below). Most defects observed in this sample are narrow, so

they are not specified in Table A.3, but in cases where the margins of a (wider) defect

could be measured, both distances from the CEJ are indicated. Multiple defects in a

single tooth are differentiated as “a”, “b” or “c”.

A.4 Estimation of Dental Defect Timing

In any study of dental material, especially one identifying a transition such as

weaning, an important consideration is the timing of enamel formation. While human

dental development is generally well understood, it is based on the primary assumption

that it is a regular or linear process. As a result, the standards outlined by Massler,

Schour and Poncher (1941) continue to form the bases of dental research involving

development time, as well as the determination of ancient subadult age (see review in

Goodman and Song 1999).

Current research, however, suggests that enamel development is far more complex.

Extensive findings indicate that enamel secretion is not linear across the entire period of

development, with a noticeably reduced rate of secretion at the cervical margin of

crowns, i.e., near the end of crown formation (see Beynon et al. 1998; Reid et al. 1998;

Reid and Dean 2000). Additionally, the delay between enamel secretion and maturation

(mineralization) is not fully understood, especially the extent of intratooth variation in

mineralization rates (L. Humphrey, pers. communication, 2004). For instance, the final

stages of enamel secretion, near the CEJ, may take several months to fully mineralize due

to a prolonged maturation process (Beynon et al. 1998; Reid and Dean 2000).

312

Even though Massler and coworkers’ (1941) ages of crown initiation and completion

(total duration) generally agree with (European) histological data (Liversidge 1994; Reid

and Dean 2000), deceleration of enamel formation in the CEJ third means that the period

between cusp tip and CEJ third will be truncated compared to their standards. For

enamel defects, which commonly occur in the mid-crown or cervical third region, the

outcome will be earlier ages of enamel and enamel defect formation (also see below).

The non-linear rate of enamel formation may represent the greatest source of

variation in standards of enamel development. However, as the extent of such variation

is not completely understood, and because of methodological issues and research

comparability, enamel development continues to be regarded as a linear process, with the

standards of Massler, Schour and Poncher (1941) being the primary reference data.

Other sources of variation in the estimation of enamel formation time include

population and sex differences, buried cuspal enamel and the choice of developmental

standard (see Goodman and Song 1999). Of these, “buried” or appositional enamel can

account for significant differences in the age of permanent enamel and (macroscopic)

enamel defect formation. This enamel represents the initial period of crown formation,

when Striae of Retzius form partial circles that begin and end in the inner enamel

(Goodman and Rose 1990: Fig. 1). Significant and observable time lapses exist between

this initial matrix formation and the appearance of Striae of Retzius on the outer enamel

surface, when they are visible macroscopically. Histological evidence suggests extensive

variation (e.g., Bullion 1987; Dean and Beynon 1991; FitzGerald 1995), but it is

reasonable to assume that little if any visible surface enamel develops before the end of

the first year in anterior permanent teeth, including canines (Reid and Dean 2000).

313

Additionally, timing of enamel development in this study accounts for population

differences in permanent canine crown completion. Numerous studies suggest that

permanent canines of North American indigenous populations complete crown formation

earlier than the white European standards of Massler and colleagues, i.e., 4.5 years

instead of 6.0 and 6.5 years for maxillary and mandibular canines, respectively (see

Anderson et al. 1976; Fanning and Brown 1971; Ubelaker 1989). Wright (1994) and

Song (1997) have applied this earlier age of canine completion to ancient Maya teeth,

which has resulted in slightly earlier mean ages of defect formation. However, as the

evidence has not been substantiated histologically, and 4.5 years is thought to be rather

early for permanent canines (A. Goodman, pers. communication, 2003), in this analysis,

they are considered complete at 5.0 years for maxillary teeth and 5.5 years for mandibular

teeth.

Regarding gender, some evidence indicates that females are advanced compared to

males in dental development (Demirjian 1986; Demirjian and Levesque 1980; Moorrees

et al. 1963). However, as noted by Smith (1991: 165), the patterned differences in rates

of enamel formation (population and sex-related) “may not be large”, i.e., 2-3%

(Demirjian and Levesque 1980; Garn et al. 1958; Gleiser and Hunt 1955).

The following regression formulae (Table A.1) are employed to arrive at the age at

which enamel defects developed in Lamanai canines. The equations inherently imply

that enamel growth is linear, and in this study, they account for 1) earlier canine crown

completion age for aboriginal populations; 2) one year of buried cuspal enamel; and

3) sample-specific mean unworn crown heights, which are 0.96 to 1.4 mm longer than the

Swedish standards (Swardstedt 1966) often used.

314

Table A.1 Regression formulae for calculation of timing of enamel defect formation

in Lamanai canines

Tooth Type

Mean Unworn Crown Height

(in mm)

Age of Enamel Formation

(in years)

Regression

Formulae*

Mean

S.D.

N

Initial

At Cusp

At CEJ

Maxillary C 11.027 0.711 20 0 1.0 5.0 Age = -0.363x + 5.0

Mandibular C 11.160 0.764 19 0.5 1.5 5.5 Age = -0.358x + 5.5

* where x equals the distance of the enamel defect (in mm) from the cemento-enamel junction (CEJ)

A.5 Timing of Lamanai Dental Defects

As one of the most hypoplastic teeth, permanent canines are a useful indicator of the

degree of health stress that afflicted individuals during early childhood (Skinner and

Goodman 1992). Based on permanent canines, 32 out of 60 Lamanai individuals (53.3%)

exhibit hypoplastic defects. This is consistent with the total Lamanai dental data, where

only 20-44% of the population have been found to be affected by hypoplastic defects at

different times in the site’s history (White 1986: Appendix N). Similarly, 20-57% of

Preclassic Cuello Maya exhibited enamel hypoplasias (Saul and Saul 1991).

However, these rates are noticeably low compared to most ancient Maya samples,

namely 87.4% incidence among Altun Ha individuals (Song 1997), 90.4% of Tipu Maya

(Cohen et al. 1994), and as much as 99% of Classic period individuals at Barton Ramie,

Seibal and Tikal (Danforth 1986). Similarly high rates also characterize the populations

at Aguateca and Dos Pilas (Wright 1994), Altar de Sacrificios (Saul 1972), Barton Ramie

(Danforth 1986), Copan (Storey 1992; Whittington 1992), Lubaantun (Saul 1975), Seibal

315

(Danforth 1986), Tancah (Saul 1982) and Tikal (Danforth 1986). For all samples,

including Lamanai, most hypoplasias are mild or moderate in severity.

On an individual level, 15 of 26 Postclassic individuals have a canine with enamel

defects (57.7%), which is comparable to the Historical sample: 17 of 34 individuals

(50%). Besides temporal correspondence, enamel hypoplasias also do not differ

significantly between Lamanai males and females and between children and adults

(White 1986; Wright 1990). Like comparisons with other Maya samples, the 50%

incidence among Historical Lamanai individuals is significantly lower than the 89% rate

of enamel hypoplasia among enslaved African Americans, who are one of the most

hypoplastic colonial populations (Blakey et al. 1994).

The incidence of longer-term, wide, enamel defects is also similar for both Lamanai

cohorts: 2 out of 15 Postclassic individuals and 3 out of 17 Historical individuals have a

single period of chronic stress (defect wider than 0.4 mm). These long-term stress

episodes (i.e., 2 months or more) occur at all ages of enamel development, but the

predominant period of broad defect formation is 4-4.5 years of age.

In terms of multiple defects, however, there is a significant temporal distinction.

While 1 out of 15 (6.7%) Postclassic individuals has more than one enamel defect, 6 out

of 17 (35.3%) Historical individuals with hypoplasia have multiple defects. A two

sample t-test indicates significance at the 0.05 level (p=0.047). This temporal distinction

is not unexpected considering the epidemiological context of the colonial period (see

Chapter Two).

Among the seven individuals who experienced multiple episodes of childhood stress,

three had two distinct episodes (42.9 %) and four had three periods of ill health (57.1%)

316

(also see Table A.3) . These seven recurrently stressed individuals are composed of 5

adults (out of 24), or 20.8% of all adults with enamel hypoplasia, and 2 children (out of

8), or 25% of all affected subadults, which are comparatively equal. Thus, it would seem

that experiencing multiple stress episodes did not necessarily determine whether an

individual died as a child, or survived into adulthood.

Nevertheless, with multi-stressed individuals only comprising 21.9% (7/32) of the

total sample of hypoplastic individuals (or 11.7% of the total sample examined in this

analysis), it appears that recurrent health or dietary insults were fairly uncommon in

Lamanai children. In comparison, Altun Ha Maya with multiple enamel defects make up

42.5% of the total number of hypoplastic individuals at the site (Song 1997).

With respect to age distribution, Figures A.2 and A.3 illustrate the unimodal

distribution of defects for each half-year age interval among Postclassic and Historical

individuals. All defect timings are represented, including multiple defects occurring in

single individuals. In individuals with an episode of long-term stress, only the initial 0.5

year interval (age at onset) was counted.

It is clear from the graphs that the vast majority of defects developed between the ages

of three to five years. This is echoed in the entire Lamanai dental sample (White 1986).

In terms of crown distribution, the majority of defects occur in the region of the mid-

crown to cervical third. The pattern of peak enamel defects between three and five years

of age is a consistent finding in lowland Maya samples from the Preclassic to Historical

period, namely at nearby Altun Ha (Song 1997), Aguateca and Dos Pilas (Wright 1994),

Altar de Sacrificios (Saul 1972), Barton Ramie, Seibal and Tikal (Danforth 1986), Cuello

(Saul and Saul 1991), Tancah (Saul 1982), and Tipu (Cohen et al. 1994).

317

Figure A.2 Distribution of defect timings in Lamanai maxillary canines

(5 Postclassic with 7 defects; 7 Historical with 14 defects)

Figure A.3 Distribution of defect timings in Lamanai mandibular canines

(10 Postclassic with 10 defects; 10 Historical with 12 defects)

Distribution of Enamel Defect Timings in Upper Canines

0

1

2

3

4

5

6

7

8

9

2.5-2.99 3.0-3.49 3.5-3.99 4.0-4.49 4.5-4.99

Age Category

Num

ber

of

Defe

cts

Postclassic

Historical

Distribution of Enamel Defect Timings in Lower Canines

0

1

2

3

4

5

6

7

8

9

2.5-2.99 3.0-3.49 3.5-3.99 4.0-4.49 4.5-4.99

Age Category

Num

ber

of

Defe

cts

Postclassic

Historical

318

Table A.2 outlines the mean age of defect formation for permanent maxillary and

mandibular canines. It appears that enamel defects recording health or dietary stress

occur most often between the ages of 3.5 and 4.5 years.

Table A.2 Average ages of enamel defect formation in the Lamanai sample

(including teeth with multiple episodes)

Tooth

Mean Age

S.D.

No. of Defects

Postclassic

Max. C 3.83 0.64 7

Mand. C 4.31 0.25 10

Historical

Max. C 3.68 0.35 14

Mand. C 4.27 0.27 12

The table and graphical data clearly reflect the significant difference in mean ages of

enamel defect formation between maxillary and mandibular canines (ANOVA result of

p=0.000012). This is due to differences in the age at which canine enamel is attributed to

commence and complete development, which is 0.5 years later in mandibular teeth

(Massler et al. 1941). Despite the slight delay, one expects defect timing between the

mandibular and maxillary teeth to be comparable. Dissimilar mean values suggests that

the existing understanding of canine enamel formation, with mandibular canines

developing at the same rate and duration 0.5 years later than maxillary teeth, should be

reconsidered.

319

Finally, as mentioned previously, enamel hypoplastic defects are valuable for gauging

the physiological consequences of infant weaning. Assuming that weaning stress can be

recognized in enamel defects, Skinner and Goodman (1992) suggest that the age of first

defect formation, which is based on Corruccini and coworkers (1985), would be the most

appropriate indicator. Specifically, if lactation provides health buffering from stress, one

would expect a narrow distribution of ages at the first occurrence of hypoplasia, which

might indicate a “culturally sanctioned age at weaning” (Skinner and Goodman 1992:

169).

Ages of first defect formation lower the mean ages of total defect timing outlined in

Table A.2. In this case, timing of maxillary canine defects average 3.61 years

(S.D.=0.70) in Postclassic individuals and 3.56 years (S.D.=0.40) in Historical

individuals, while mandibular defects develop at a mean age of 4.29 years (S.D.=0.27) in

Postclassic individuals and 4.18 years (S.D.=0.27) in Historical individuals. Although

the sample size is limited, these ages correspond well with the late peaking of enamel

Sr/Ca observed in this study, in addition to ethnohistorical evidence of weaning.

A.6 Dental Health Raw Data

Table A.3 includes all the macroscopic dental data that was collected in this study for

the sixty ablated Lamanai canines, which was used to assess general dental “health”.

These details include crown height, dental attrition, caries, degree of calculus deposits,

measurement of enamel hypoplasias, age of enamel defect formation and additional

comments. Scoring criteria are detailed in each heading, with CEJ referring to the

cemento-enamel junction.

320

Table A.3 Dental health details for Lamanai canines

Individual # Sex/Age Tooth Type Crown

Height

Dental

Attrition Caries Calculus

Enamel Defect

Measurement

Age of Defect

Formation Comments

N10-2 = Postclassic

N10-4 = Postclassic

YDL-85 = Historical

F=female

M=male

Ad.=adult

SubAd.=

subadult (ages in years)

Up=upper

Lo=lower

R=right

L=left

Measured

from cusp tip

to cemento

enamel

junction (CEJ)

in mm

0=none

1=slight

2=moderate

3=moderate-

heavy 4=severe

0=none

1-3 =

number of

carious

lesions

0=none

1=slight

2=moderate

3=heavy

4=very heavy

distance in mm

from middle of

defect to CEJ,

1-3 = defect severity

(see Song 1997) a-c=separate

defect occurrences

in years,

based

on Regression

Formulae

(Table A.1)

H=hypocalcification

(W-white, B-brown,

O-orange, C-cream)

LAM N10-2/4 F 14-18 Lo LC 9.63 2 0 1-2 2/3: 2.99 - 4.16 4.01-4.43 depression at CEJ 1/3

LAM N10-2/5 M Ad. Lo RC 9.65 1-2 0 0 0 0 crack across lingual enam / root

LAM N10-2/16 SubAd. Up LC 11.63 0 0 0 0 0 White scratched areas

LAM N10-2/20 M Ad. Lo RC 9.60 2 0 1-2 at CEJ approx. 2.21 or CEJ

1/4 4.71 Rough patch; elite individ.

LAM N10-2/21 10-12 Up RC 11.12 0 0 0 0 0 some H-OB stains

LAM N10-2/22 M Ad. Lo LC 10.56 2 0 2 1 shallow LEH at

CEJ 1/4-1/3 approx. 4.17 small vertical crack

LAM N10-2/40 Ad. M? Up RC 11.89 1-2 0 1-2 0 0 vertical midline crack

LAM N10-2/42 M 20-30 Lo RC 11.53 1-2 0 1-2 2: 3.95 4.09 -

LAM N10-2/44 7-8 Up LC 11.01 0 0 0 pit- mid is 3.80 3.62 vertical LEH coming from

pit- ends at 7.43

LAM N10-2/49 10-11 Lo RC 11.30 1 0 0 0 0 glued at CEJ 1/3 line; brown

staining all over (H?)

Continued, next page

321

Table A.3, continued


Height

Dental


Enamel Defect

Measurement

Age of Defect

Formation Comments

N10-2 = Postclassic

N10-4 = Postclassic

YDL-85 = Historical

F=female

M=male

Ad.=adult

SubAd.=


Up=upper

Lo=lower

R=right

L=left

Measured

from cusp tip

to cemento

enamel

junction (CEJ)

in mm

0=none

1=slight

2=moderate

3=moderate-

heavy 4=severe

0=none

1-3 =

number of

carious

lesions

0=none

1=slight

2=moderate

3=heavy

4=very heavy

distance in mm

from middle of

defect to CEJ,



defect occurrences

in years,

based

on Regression

Formulae

(Table A.1)

H=hypocalcification

(W-white, B-brown,

O-orange, C-cream)

LAM N10-2/50 6-8 Up RC 11.36 0-1 0 0 a- 1: 1.37, b- 2: 2.40,

c- 2: 3.58 3.70; 4.13; 4.50 1/3 root formation

LAM N10-4/1 F >35 Up RC 10.42 1-2 0 2-3 on medial

side 1: 3.46 3.74

vertical crack at midline, H-

white

LAM N10-4/2A 14-18 Up LC 11.54 1 0 3 at CEJ 0 0 vertical crack at midline

LAM N10-4/2B F >40 Lo RC 9.96 2-3 0 2-3 2: 4.56 3.87 glued down midline crack

LAM N10-4/4 F >50 Lo LC 9.50 0 0 0 0 0 H-B/W all over

LAM N10-4/10 F 15-20 Up LC 9.91 1-2 0 2 at CEJ 2: 1.45 4.47 notched on med side

LAM N10-4/11 F? 30+ Up LC 9.04 2 0 1 at CEJ 2/3: 6.27 to 6.85 2.51-2.72 large vertical crack at

mid-line

LAM N10-4/19 F Ad+ Lo RC 10.82 1-3 0 2-3 pit at cervical 1/4 approx. 4.50 -

LAM N10-4/33 F 30-40 Up LC 9.68 1 0 1 at CEJ 0 0 -

LAM N10-4/40 F 25-30 Lo LC 10.64 2 0 1-2 1: 3.35 4.30 vertical midline crack

LAM N10-4/43 M Ad+ Up LC 8.98 2-3 0 3 at CEJ 0 0 -


322



Height

Dental


Enamel Defect

Measurement

Age of Defect

Formation Comments

N10-2 = Postclassic

N10-4 = Postclassic

YDL-85 = Historical

F=female

M=male

Ad.=adult

SubAd.=


Up=upper

Lo=lower

R=right

L=left

Measured

from cusp tip

to cemento

enamel

junction (CEJ)

in mm

0=none

1=slight

2=moderate

3=moderate-

heavy 4=severe

0=none

1-3 =

number of

carious

lesions

0=none

1=slight

2=moderate

3=heavy

4=very heavy

distance in mm

from middle of

defect to CEJ,



defect occurrences

in years,

based

on Regression

Formulae

(Table A.1)

H=hypocalcification

(W-white, B-brown,

O-orange, C-cream)

LAM N10-4/44 Ad. Lo RC 10.61 1-2 0 1 1?: 2.57 4.58 slight depressed region

cervical 1/3

LAM N10-4/45 F 30+ Lo LC 11.28 1 0 1-2 depression around

2.94 4.45 -

LAM N10-4/46A? M? Ad. Lo LC 12.06 1-2 0 2-3 0 0 long tooth; elite individ.

LAM N10-4/46B F Ad.+ Up LC 11.76 1-2 0 2 0 0 -

LAM N10-4/46C F Ad. Lo LC 11.22 0-1 0 2 1: 3.51 4.24 small tooth

LAM YDL-85/17 F 20-40 Up LC 10.48 1-2 0 1-2 at CEJ

a- 2: 2.72,

b- 1/2: 4.06,

c- 1: 5.17

3.12; 3.53; 4.01 -

LAM YDL-85/21 F 20-30 Up LC 9.52 1-2 0 1 a- 1: 3.67, b- 1: 4.35,

c- 1: 5.22 3.11; 3.42; 3.67

H-B/C on sides, some H-O on

labial surface

LAM YDL-85/23 F 20-30 Lo RC 11.21 2 0 1 at CEJ 2: 2.93 4.45 -

LAM YDL-85/27 F 20-30 Lo LC 9.09 2 0 2-3 0 0 vertical midline crack

LAM YDL-85/31 F? 20-25 Lo RC 10.17 2-3 0 2-3 1: 3.69 4.18 Depressed region? CEJ 1/3


323



Height

Dental


Enamel Defect

Measurement

Age of Defect

Formation Comments

N10-2 = Postclassic

N10-4 = Postclassic

YDL-85 = Historical

F=female

M=male

Ad.=adult

SubAd.=


Up=upper

Lo=lower

R=right

L=left

Measured

from cusp tip

to cemento

enamel

junction (CEJ)

in mm

0=none

1=slight

2=moderate

3=moderate-

heavy 4=severe

0=none

1-3 =

number of

carious

lesions

0=none

1=slight

2=moderate

3=heavy

4=very heavy

distance in mm

from middle of

defect to CEJ,



defect occurrences

in years,

based

on Regression

Formulae

(Table A.1)

H=hypocalcification

(W-white, B-brown,

O-orange, C-cream)

LAM YDL-85/32 Ad. M? Up LC 11.02 1-2 0 2-3 2: 3.61 3.69 some enamel missing on

lingual

LAM YDL-85/33 M 25-30 Lo LC 10.85 2 0 2-3 1: ~3.13 4.38 depression CEJ 1/3 ?

LAM YDL-85/35 M 30-40 Lo LC 10.25 2 0 3 0 0 -

LAM YDL-85/41 F 18-25 Up RC 9.25 1-2 0 2 0 0 crack along med-lateral axis

from tip to root

LAM YDL-85/44 5-7 Up RC 11.05 0 0 0 0 0 H - O/B along CEJ

LAM YDL-85/46 F 20-30 Up LC 9.93 2 0 1 1?: 6.74 0 vertical midline crack

LAM YDL-85/47 M 12-16 Lo LC 11.03 1-2 0 1-2

2: 2.01 to 3.86

(rough region with

lines within)

4.12-4.78

rough depressed region across

most of CEJ 1/3 (vert mid

crack)

LAM YDL-85/50B F Ad. Up LC 11.04 1-2 0 1 1?: 6.18 0 2nd individual

LAM YDL-85/53 F 16-23 Lo RC 11.43 1 0 1 0 0 H-W/C in CEJ 1/3 region


324



Height

Dental


Enamel Defect

Measurement

Age of Defect

Formation Comments

N10-2 = Postclassic

N10-4 = Postclassic

YDL-85 = Historical

F=female

M=male

Ad.=adult

SubAd.=


Up=upper

Lo=lower

R=right

L=left

Measured

from cusp tip

to cemento

enamel

junction (CEJ)

in mm

0=none

1=slight

2=moderate

3=moderate-

heavy 4=severe

0=none

1-3 =

number of

carious

lesions

0=none

1=slight

2=moderate

3=heavy

4=very heavy

distance in mm

from middle of

defect to CEJ,



defect occurrences

in years,

based

on Regression

Formulae

(Table A.1)

H=hypocalcification

(W-white, B-brown,

O-orange, C-cream)

LAM YDL-85/54 5-7 Up LC 11.85 0 0 0 1?: 4.27 0 crown only

LAM YDL-85/59 6-7 Lo LC 11.41 0 0 0 1: 4.85 3.76 crown only

LAM YDL-85/62 F 20-25 Up LC 9.50 1 0 1 0 0 crack along medial-lateral

axis thru to root tip

LAM YDL-85/63 6 Lo RC 11.86 0 0 0 1: 3.91 line, (border

of CEJ 1/3 rough) 4.10 H-B/W in CEJ 1/3

LAM YDL-85/65 6-7 Up RC 10.40 0 0 0 0 0 H-B along CEJ

LAM YDL-85/68b 8-12 Up RC 11.12 1 0 1 pit/rough patch: 2.44 4.11 small midline crack

LAM YDL-I-68? M 20-30 Up LC 9.49 1-2 0 1 0 0 small midline crack,

glued in several places

LAM YDL-85/71A 7-8 Lo LC 10.92 0 0 0 a- 2: 2.74

b- 2: 4.02 4.06; 4.52 H-B(?) along CEJ

LAM YDL-85/73 M? 20-25 Lo LC 10.43 1-2 0 2 0 0 -


325



Height

Dental


Enamel Defect

Measurement

Age of Defect

Formation Comments

N10-2 = Postclassic

N10-4 = Postclassic

YDL-85 = Historical

F=female

M=male

Ad.=adult

SubAd.=


Up=upper

Lo=lower

R=right

L=left

Measured

from cusp tip

to cemento

enamel

junction (CEJ)

in mm

0=none

1=slight

2=moderate

3=moderate-

heavy 4=severe

0=none

1-3 =

number of

carious

lesions

0=none

1=slight

2=moderate

3=heavy

4=very heavy

distance in mm

from middle of

defect to CEJ,



defect occurrences

in years,

based

on Regression

Formulae

(Table A.1)

H=hypocalcification

(W-white, B-brown,

O-orange, C-cream)

LAM YDL-85/78A M Ad. Lo RC 11.86 1-2 0 2 a- 1: 2.99

b- 2: 4.45 3.91; 4.43

small midline crack, enamel

missing from part of labial,

mark root for cut

LAM YDL-85/78C F Ad. Lo RC 10.02 1-2 0 1 2: 2.24 4.70 rough area and H-OB at CEJ 1/3

region, small midline crack

LAM YDL-85/80 8-9 Lo LC 12.87 0 0 0 0 0 midline crack

LAM YDL-85/86 M? 20-25 Up LC 9.95 2 0 1 a- 2: 2.99

b- 2: 4.46 3.38; 3.91 -

LAM YDL-85/87B M 30-40 Up C 10.79 1 0 1-2 0 0 small midline crack

LAM YDL-85/91A 8-10 Lo LC 10.46 0 0 0

a- 2: 3.24,

b- 2 (pit area): 3.69

(is same pd.)

4.18-4.34

midline crack & some labial

enamel missing, plus vertical

LEH (?) along lat. labial in

midcrown region (1.70mm long)


326



Height

Dental


Enamel Defect

Measurement

Age of Defect

Formation Comments

N10-2 = Postclassic

N10-4 = Postclassic

YDL-85 = Historical

F=female

M=male

Ad.=adult

SubAd.=


Up=upper

Lo=lower

R=right

L=left

Measured

from cusp tip

to cemento

enamel

junction (CEJ)

in mm

0=none

1=slight

2=moderate

3=moderate-

heavy 4=severe

0=none

1-3 =

number of

carious

lesions

0=none

1=slight

2=moderate

3=heavy

4=very heavy

distance in mm

from middle of

defect to CEJ,



defect occurrences

in years,

based

on Regression

Formulae

(Table A.1)

H=hypocalcification

(W-white, B-brown,

O-orange, C-cream)

LAM YDL-85/97 M 25-30 Up LC 10.23 2 0 1 a- 1: 2.26, b- 2: 3.11,

c- 2: 4.17 3.49; 3.87; 4.18

some enam missing on labial

near CEJ; small midline crack

LAM YDL-85/98 M Ad. Up LC 9.49 2 0 1 0 0 midline crack

LAM YDL-85/101 F Ad. Up RC 11.48 1 0 1-2 0 0

glued midline crack, portion of

tooth at ling CEJ gone, glued

here

LAM YDL-85/102 F 30-35 Lo LC 8.95 1-2 0 2-3 0 0 small tooth

LAM YDL-85/103 M 30-40 Up RC 11.40 2 0 1 1-bit wide at CEJ 1/4-

1/5

mid at approx.

4.00

some enam gone around medial

side of labial

327

APPENDIX B

ABLATION DETAILS FOR LAMANAI CANINES

Tables B.1 – B.4 outline the ablation details for all Lamanai teeth analyzed in this

study, which are based on photographic measurements (see Chapter Six). They are

grouped into maxillary and mandibular teeth for consistency of enamel developmental

period and the “ages” (in years) represented in each ablation. The specific details are

described below:

Ablation detail

Explanation

1ST LA

Length of first ablation in micrometers (cusp tip end)

2ND LA Length of second ablation in micrometers

3RD LA Length of third ablation in micrometers (CEJ end)

Total Ablation Length Total length of all ablations (along axis of crown)

Total # Readings Total number of ICP-MS element readings

Microns per reading Mean number of micrometers per element reading

CEJ enamel not ablated Length of enamel at CEJ end not ablated

"Missing" cusp enamel (extrap.) Length of enamel extrapolated to be missing from cusp

Crown Height Total (microns) Total height of crown in micrometers (along central axis)

Microns Per half year Mean number of micrometers per half year period

Start Age with Cuspal enam (0.5/1 yr) Age of start of 1st ablation, accounting for cuspal enamel

time that is not sampled (approx. 0.5 years)

End Age of 5/5.5 years End age of last sampled enamel (at end of last ablation)

Total years covered by ablations Total number of years sampled by all ablations

LA1 Reading #'s Element reading numbers of first ablation

Years detailed in LA1 Number of years represented in first ablation

LA2 Reading #'s Element reading numbers of second ablation

Years detailed in LA2 Number of years represented in second ablation

LA3 Reading #'s Element reading numbers of third ablation

Years detailed in LA3 Number of years represented in third ablation

Table B.1 Ablation details for Postclassic Lamanai maxillary canines

Individual # N10-2/16 N10-2/21 N10-2/40 N10-2/44 N10-2/50 N10-4/1

1ST LA (microns) 9290 5540 6480 10500 6120 7130

2ND LA (microns) 1750 3000 4470 1320 4060 2550

3RD LA (microns) - 1580 - - - -

Total Ablation Length 11040 10120 10950 11820 10180 9680

Total # Readings 795 799 863 842 810 734

Microns per reading 13.887 12.666 12.688 14.038 12.568 13.188

CEJ enamel not ablated 420 750 470 420 780 500

"Missing" cusp enamel (extrap.) 380 300 1240 320 700 860

Crown Height Total (microns) 11840 11170 12660 12560 11660 11040

Microns Per half year 1315.556 1241.111 1406.667 1395.556 1295.556 1226.667

Start Age with Cuspal enam (0.5yr) 0.644 0.621 0.941 0.615 0.770 0.851

End Age of 5 years 4.840 4.698 4.833 4.850 4.699 4.796

# Readings per half year: 94.734 97.989 110.863 99.413 103.084 93.014

Total years covered by ablations 4.196 4.077 3.892 4.235 3.929 3.946

LA1 Reading #'s 1-665 1-436 1-511 1-746 1-493 1-533

Years detailed in LA1 0.644-4.175 0.621-2.853 0.941-3.244 0.615-4.377 0.770-3.132 0.851-3.757

LA2 Reading #'s 666-795 437-679 512-863 747-842 494-810 534-734


LA3 Reading #'s - 680-799 - - - -

Years detailed in LA3 - 4.063-4.698 - - - -


328

Table B.1, continued

Individual # N10-4/2A N10-4/10 N10-4/11 N10-4/33 N10-4/43 N10-4/46B

1ST LA (microns) 6330 7400 5700 8045 6010 8880

2ND LA (microns) 3170 1160 2240 2225 2870 -

3RD LA (microns) 1220 1700 - - - -

Total Ablation Length 10720 10260 7940 10270 8880 8880

Total # Readings 780 774 630 755 673 627

Microns per reading 13.744 13.256 12.603 13.603 13.195 14.163

CEJ enamel not ablated 140 180 300 250 200 3030

"Missing" cusp enamel (extrap.) 1260 805 560 340 1900 620

Crown Height Total (microns) 12120 11245 8800 10860 10980 12530

Microns Per half year 1346.667 1249.444 977.778 1206.667 1220.000 1392.222

Start Age with Cuspal enam (0.5yr) 0.968 0.822 0.786 0.641 1.279 0.723

End Age of 5 years 4.948 4.928 4.847 4.896 4.918 3.912

# Half year periods: 7.960 8.212 8.120 8.511 7.279 6.378

# Readings per half year: 97.985 94.256 77.582 88.708 92.462 98.302

Total years covered by ablations 3.980 4.106 4.060 4.256 3.639 3.189

LA1 Reading #'s 1-451 1-544 1-441 1-571 1-442 1-627


LA2 Reading #'s 452-687 545-637 442-630 572-755 443-673 -

Years detailed in LA2 3.319-4.496 3.784-4.248 3.702-4.847 3.975-4.896 3.743-4.918 -

LA3 Reading #'s 688-780 638-774 - - - -

Years detailed in LA3 4.497-4.948 4.249-4.928 - - - -

329

Table B.2 Ablation details for Postclassic Lamanai mandibular canines

Individual # N10-2/4 N10-2/5 N10-2/20 N10-2/22 N10-2/42 N10-2/49 N10-4/2B

1ST LA (microns) 5990 6750 8580 5410 6120 4780 2620

2ND LA (microns) 2760 2030 2540 2550 3080 5420 4805

3RD LA (microns) 500 - - 1300 1090 1200 2650

Total Ablation Length 9250 8780 11120 9260 10290 11400 10075

Total # Readings 698 713 828 760 773 859 776

Microns per reading 13.252 12.314 13.430 12.184 13.312 13.271 12.983

CEJ enamel not ablated 460 300 280 600 310 575 505

"Missing" cusp enamel (extrap.) 1400 480 420 1150 380 300 525

Crown Height Total (microns) 11110 9560 11820 11010 10980 12275 11105

Microns Per half year 1234.444 1062.222 1313.333 1223.333 1220.000 1363.889 1233.889

Start Age with Cuspal enam (1yr) 1.567 1.226 1.160 1.470 1.156 1.110 1.213

End Age of 5.5 years 5.314 5.359 5.393 5.255 5.373 5.289 5.295

# Half year periods: 7.493 8.266 8.467 7.569 8.434 8.358 8.165

# Readings per half year: 93.151 86.260 97.791 100.403 91.648 102.770 95.037

Total years covered by ablations 3.747 4.133 4.234 3.785 4.217 4.179 4.083

LA1 Reading #'s 1-453 1-541 1-634 1-451 1-454 1-365 1-206

Years detailed in LA1 1.567-3.993 1.226-4.403 1.160-4.426 1.470-3.681 1.156-3.664 1.110-2.862 1.213-2.274

LA2 Reading #'s 454-646 542-713 635-828 452-656 455-676 366-768 207-549


LA3 Reading #'s 647-698 - - 657-760 677-773 769-859 550-776

Years detailed in LA3 5.113-5.314 - - 4.725-5.255 4.928-5.373 4.851-5.289 4.223-5.295


330


Individual # N10-4/4 N10-4/19 N10-4/40 N10-4/44 N10-4/45 N10-4/46A N10-4/46C

1ST LA (microns) 3850 7340 4860 7000 5700 8150 5650

2ND LA (microns) 2610 2200 4540 3480 5000 3550 5870

3RD LA (microns) 0 - - 800 - - -

Total Ablation Length 6460 9540 9400 11280 10700 11700 11520

Total # Readings 481 702 772 800 832 808 830

Microns per reading 13.430 13.590 12.176 14.100 12.861 14.480 13.880

CEJ enamel not ablated 1440 1180 450 530 300 560 325

"Missing" cusp enamel (extrap.) 580 275 1200 200 300 230 260

Crown Height Total (microns) 8480 10995 11050 12010 11300 12490 12105

Microns Per half year 942.222 1221.667 1227.778 1334.444 1255.556 1387.778 1345.000

Start Age with Cuspal enam (1yr) 1.308 1.113 1.489 1.075 1.119 1.083 1.097

End Age of 5.5 years 4.736 5.017 5.317 5.301 5.381 5.298 5.379

# Half year periods: 6.856 7.809 7.656 8.453 8.522 8.431 8.565

# Readings per half year: 70.156 89.896 100.835 94.641 97.628 95.840 96.905

Total years covered by ablations 3.428 3.905 3.828 4.226 4.261 4.215 4.283

LA1 Reading #'s 1-286 1-542 1-370 1-500 1-448 1-560 1-425


LA2 Reading #'s 287-481 543-702 371-772 501-746 449-832 561-808 426-830


LA3 Reading #'s - - - 747-800 - - -

Years detailed in LA3 - - - 5.004-5.301 - - -

331

Table B.3 Ablation details for Historical Lamanai maxillary canines

Individual # YDL-I/68 YDL-85/17 YDL-85/21 YDL-85/32 YDL-85/41 YDL-85/44 YDL-85/46 YDL-85/50B YDL-85/54

1ST LA (microns) 9000 6700 6980 7980 7100 7080 6880 8075 6965

2ND LA (microns) 700 2600 2620 2930 - 4430 3880 1700 3695

3RD LA (microns) - - - - - - 620 - 700

Total Ablation Length 9700 9300 9600 10910 7100 11510 11380 9775 11360

Total # Readings 707 760 739 807 578 855 854 712 841

Microns per reading 13.720 12.237 12.991 13.519 12.284 13.462 13.326 13.729 13.508

CEJ enamel not ablated 180 300 420 730 600 490 230 405 260

"Missing" cusp enamel (extrap.) 800 500 375 710 1450 280 380 560 390

Crown Height Total (microns) 10680 10100 10395 12350 9150 12280 11990 10740 12010

Microns Per half year 1186.667 1122.222 1155.000 1372.222 1016.667 1364.444 1332.222 1193.333 1334.444

Start Age with Cuspal enam (0.5yr) 0.837 0.723 0.662 0.759 1.213 0.603 0.643 0.735 0.646

End Age of 5 years 4.924 4.866 4.818 4.734 4.705 4.820 4.914 4.830 4.903

# Half year periods: 8.174 8.287 8.312 7.951 6.984 8.436 8.542 8.191 8.513

# Readings per half year: 86.492 91.708 88.911 101.502 82.765 101.355 99.975 86.921 98.791

Total years covered by ablations 4.087 4.144 4.156 3.975 3.492 4.218 4.271 4.096 4.256

LA1 Reading #'s 1-656 1-548 1-523 1-589 1-578 1-525 1-516 1-590 1-515

Years detailed in LA1 0.837-4.629 0.723-3.708 0.662-3.684 0.759-3.666 3.492 0.603-3.197 0.643-3.225 0.735-4.118 0.646-3.256

LA2 Reading #'s 657-707 549-760 524-739 590-807 - 526-855 517-804 591-712 516-787

Years detailed in LA2 4.630-4.924 3.709-4.866 3.685-4.818 3.667-4.734 - 3.198-4.820 3.226-4.681 4.119-4.830 3.257-4.641

LA3 Reading #'s - - - - - - 805-854 - 788-841

Years detailed in LA3 - - - - - - 4.682-4.914 - 4.642-4.903


332


Individual # YDL-85/62 YDL-85/65 YDL-85/68 YDL-85/86 YDL-85/87B YDL-85/97 YDL-85/98 YDL-85/101 YDL-85/103

1ST LA (microns) 6335 8420 6840 7260 7730 6220 7500 6985 8890

2ND LA (microns) 3170 710 3220 2000 3450 3770 900 1500 2290

3RD LA (microns) - 1140 - - - - - 1540 -

Total Ablation Length 9505 10270 10060 9260 11180 9990 8400 10025 11180

Total # Readings 689 758 814 684 818 728 712 780 813

Microns per reading 13.795 13.549 12.359 13.538 13.667 13.723 11.798 12.853 13.752

CEJ enamel not ablated 825 620 200 640 370 715 320 625 1040

"Missing" cusp enamel (extrap.) 830 620 640 1050 1120 960 1500 725 1620

Crown Height Total (microns) 11160 11510 10900 10950 12670 11665 10220 11375 13840

Microns Per half year 1240.000 1278.889 1211.111 1216.667 1407.778 1296.111 1135.556 1263.889 1537.778

Start Age with Cuspal enam (0.5yr) 0.835 0.742 0.764 0.932 0.898 0.870 1.160 0.787 1.027

End Age of 5 years 4.667 4.758 4.917 4.737 4.869 4.724 4.859 4.753 4.662

# Half year periods: 7.665 8.030 8.306 7.611 7.942 7.708 7.397 7.932 7.270

# Readings per half year: 89.885 94.391 97.996 89.870 103.002 94.451 96.252 98.337 111.826

Total years covered by ablations 3.833 4.015 4.153 3.805 3.971 3.854 3.699 3.966 3.635

LA1 Reading #'s 1-464 1-627 1-550 1-535 1-554 1-462 1-623 1-534 1-652

Years detailed in LA1 0.835-3.389 0.742-4.034 0.764-3.588 0.932-3.915 0.898-3.643 0.870-3.270 1.160-4.463 0.787-3.550 1.027-3.917

LA2 Reading #'s 465-689 628-672 551-814 536-684 555-818 463-728 624-712 535-657 653-813

Years detailed in LA2 3.390-4.667 4.035-4.313 3.589-4.917 3.916-4.737 3.644-4.869 3.271-4.724 4.464-4.859 3.551-4.144 3.918-4.662

LA3 Reading #'s - 673-758 - - - - - 658-780 -

Years detailed in LA3 - 4.314-4.758 - - - - - 4.145-4.753 -

333

Table B.4 Ablation details for Historical Lamanai mandibular canines

Individual # YDL-85/23 YDL-85/27 YDL-85/31 YDL-85/33 YDL-85/35 YDL-85/47 YDL-85/53 YDL-85/59

1ST LA (microns) 5870 5580 5290 5380 6400 6550 7130 5480

2ND LA (microns) 4010 3370 4240 3860 2980 3670 4010 4420

3RD LA (microns) 1080 860 1400 - - - 790 700

Total Ablation Length 10960 9810 10930 9240 9380 10220 11930 10600

Total # Readings 817 687 817 742 749 741 868 850

Microns per reading 13.415 14.279 13.378 12.453 12.523 13.792 13.744 12.471

CEJ enamel not ablated 360 180 240 620 250 900 300 460

"Missing" cusp enamel (extrap.) 700 650 860 420 520 330 550 440

Crown Height Total (microns) 12020 10640 12030 10280 10150 11450 12780 11500

Microns Per half year 1335.556 1182.222 1336.667 1142.222 1127.778 1272.222 1420.000 1277.778

Start Age with Cuspal enam (1yr) 1.262 1.275 1.322 1.184 1.231 1.130 1.194 1.172

End Age of 5.5 years 5.365 5.424 5.410 5.229 5.389 5.146 5.394 5.320

# Half year periods: 8.206 8.298 8.177 8.089 8.317 8.033 8.401 8.296

# Readings per half year: 99.557 82.792 99.914 91.724 90.054 92.242 103.316 102.463

Total years covered by ablations 4.103 4.149 4.089 4.045 4.159 4.017 4.201 4.148

LA1 Reading #'s 1-429 1-411 1-399 1-429 1-511 1-475 1-523 1-431

Years detailed in LA1 1.262-3.460 1.275-3.635 1.322-3.300 1.184-3.539 1.231-4.068 1.130-3.704 1.194-3.704 0.646-3.256

LA2 Reading #'s 430-732 412-636 400-715 430-742 512-749 476-741 524-805 432-783


LA3 Reading #'s 733-817 637-687 716-817 - - - 806-868 784-850

Years detailed in LA3 4.963-5.365 5.062-5.424 4.888-5.410 - - - 5.118-5.394 4.642-4.903


334


Individual # YDL-85/63 YDL-85/71A YDL-85/73 YDL-85/78A YDL-85/78C YDL-85/80 YDL-85/91A YDL-85/102

1ST LA (microns) 5340 6410 6090 8180 7100 10640 9020 6950

2ND LA (microns) 5280 3640 4730 2060 2680 3200 1500 1410

3RD LA (microns) - - - - - - - -

Total Ablation Length 10620 10050 10820 10240 9780 13840 10520 8360

Total # Readings 782 758 810 833 709 969 769 605

Microns per reading 13.581 13.259 13.358 12.293 13.794 14.283 13.680 13.818

CEJ enamel not ablated 1030 380 540 540 520 400 210 620

"Missing" cusp enamel (extrap.) 640 290 580 540 700 100 475 820

Crown Height Total (microns) 12290 10720 11940 11320 11000 14340 11205 9800

Microns Per half year 1365.556 1191.111 1326.667 1257.778 1222.222 1593.333 1245.000 1088.889

Start Age with Cuspal enam (1yr) 1.234 1.122 1.219 1.215 1.286 1.031 1.191 1.377

End Age of 5.5 years 5.123 5.340 5.296 5.285 5.287 5.374 5.416 5.215

# Half year periods: 7.777 8.438 8.156 8.141 8.002 8.686 8.450 7.678

# Readings per half year: 100.552 89.837 99.316 102.317 88.605 111.556 91.008 78.801

Total years covered by ablations 3.889 4.219 4.078 4.071 4.001 4.343 4.225 3.839

LA1 Reading #'s 1-403 1-470 1-460 1-662 1-516 1-742 1-654 1-510


LA2 Reading #'s 404-782 471-758 461-810 663-833 517-709 743-969 655-769 511-605


LA3 Reading #'s - - - - - - - -

Years detailed in LA3 - - - - - - - -

335

336

APPENDIX C

STATISTICAL RESULTS

C.1 Comparisons of Sr/Ca Increase

Table C.1 Results of Single Factor ANOVAs comparing total Sr/Ca increase

between Postclassic children and adults

Groups Count Sum Average Variance

N10 Children 6 10.928 1.821 0.176 N10 Adults 19 34.241 1.802 0.172

Source of Variation SS df MS F P-value F crit

Between Groups 0.002 1 0.002 0.010 0.922 4.279

Within Groups 3.975 23 0.173

Total 3.977 24


between Postclassic females and males


N10 Females 12 20.631 1.719 0.211 N10 Males 7 13.609 1.944 0.092


Between Groups 0.224 1 0.224 1.325 0.266 4.451


Total 3.093 18


between Historical children and adults


YDL Children 9 16.427 1.825 0.101 YDL Adults 25 47.271 1.891 0.639


Between Groups 0.029 1 0.029 0.057 0.813 4.149


Total 16.163 33

337


between Historical females and males


YDL Females 13 26.725 2.056 0.965 YDL Males 12 20.546 1.712 0.274


Between Groups 0.737 1 0.737 1.161 0.292 4.279


Total 15.328 24


between Postclassic and Historical children


N10 Children 6 10.928 1.821 0.176 YDL Children 9 16.427 1.825 0.101


Between Groups 0.000 1 0.000 0.000 0.984 4.667


Total 1.688 14


between Postclassic and Historical females


N10 Females 12 20.631 1.719 0.211 YDL Females 13 26.725 2.056 0.965


Between Groups 0.707 1 0.707 1.170 0.291 4.279


Total 14.599 24


between Postclassic and Historical males


N10 Males 7 13.609 1.944 0.092 YDL Males 12 20.546 1.712 0.274


Between Groups 0.238 1 0.238 1.134 0.302 4.451


Total 3.806 18

338

C.2 Comparisons of Sr/Ca at 0.25 year intervals

Table C.8 Results of Single Factor ANOVAs comparing Postclassic children

and adults (Sr/Ca at 0.25 year intervals)

Postclassic Children and Adults

Groups Count Sum Average Variance df F P-value F crit

Kids 0.5 2 0.09034 0.04517 0.00005 3 15.27498 0.05967 18.51276 Ads0.5 2 0.14623 0.07312 0.00005

Kids 0.75 4 0.20988 0.05247 0.00030 9 0.56532 0.47366 5.31764 Ads0.75 6 0.37437 0.06240 0.00049

Kids 1 6 0.29717 0.04953 0.00029 19 1.04811 0.31951 4.41386 Ads1 14 0.83352 0.05954 0.00044

Kids 1.25 6 0.30785 0.05131 0.00037 23 0.49096 0.49085 4.30094 Ads1.25 18 1.04393 0.05800 0.00042

Kids 1.5 6 0.29658 0.04943 0.00026 24 1.25559 0.27405 4.27934 Ads1.5 19 1.14157 0.06008 0.00045

Kids 1.75 6 0.30671 0.05112 0.00028 24 1.40049 0.24873 4.27934 Ads1.75 19 1.18664 0.06245 0.00046

Kids 2 6 0.32747 0.05458 0.00033 24 1.05537 0.31496 4.27934 Ads2 19 1.23218 0.06485 0.00049

Kids 2.25 6 0.34680 0.05780 0.00038 24 0.85259 0.36541 4.27934 Ads2.25 19 1.26389 0.06652 0.00041

Kids 2.5 6 0.34065 0.05677 0.00035 24 1.73462 0.20079 4.27934 Ads2.5 19 1.32519 0.06975 0.00047

Kids 2.75 6 0.37256 0.06209 0.00079 24 0.85462 0.36485 4.27934 Ads2.75 19 1.38193 0.07273 0.00055

Kids 3 6 0.37283 0.06214 0.00048 24 1.75369 0.19842 4.27934 Ads3 19 1.46755 0.07724 0.00062

Kids 3.25 6 0.39215 0.06536 0.00045 24 1.54094 0.22699 4.27934 Ads3.25 19 1.51137 0.07955 0.00064

Kids 3.5 6 0.40421 0.06737 0.00032 24 1.61625 0.21632 4.27934 Ads3.5 19 1.54217 0.08117 0.00060

Kids 3.75 6 0.41496 0.06916 0.00035 24 1.50116 0.23289 4.27934 Ads3.75 19 1.57843 0.08308 0.00065

Kids 4 6 0.43063 0.07177 0.00047 23 1.49751 0.23400 4.30094 Ads4 18 1.57042 0.08725 0.00079

Kids 4.25 6 0.43395 0.07233 0.00042 23 1.55557 0.22543 4.30094 Ads4.25 18 1.61688 0.08983 0.00102

Kids 4.5 6 0.42925 0.07154 0.00044 23 2.76773 0.11036 4.30094 Ads4.5 18 1.67401 0.09300 0.00084

Kids 4.75 4 0.30462 0.07615 0.00055 19 0.85081 0.36852 4.41386 Ads4.75 16 1.45161 0.09073 0.00085

Kids 5 2 0.16001 0.08001 0.00050 12 0.60277 0.45389 4.84434 Ads5 11 1.07150 0.09741 0.00089

Kids 5.25 3 0.25276 0.08425 0.00081 12 0.09161 0.76778 4.84434 Ads5.25 10 0.89269 0.08927 0.00060

339

Table C.9 Results of Single Factor ANOVAs comparing Postclassic females

and males (Sr/Ca at 0.25 year intervals)

Postclassic Females and Males


Fem0.75 5 0.33568 0.06714 0.00044 5 1.53018 0.28375 7.70865 Male0.75 1 0.03870 0.03870 N/A

Fem1 9 0.55501 0.06167 0.00048 13 0.24351 0.63059 4.74722 Male1 5 0.27851 0.05570 0.00044

Fem1.25 11 0.68828 0.06257 0.00049 17 1.43833 0.24787 4.49400 Male1.25 7 0.35565 0.05081 0.00028

Fem1.5 12 0.76424 0.06369 0.00052 18 0.92622 0.34934 4.45132 Male1.5 7 0.37733 0.05390 0.00034

Fem1.75 12 0.78660 0.06555 0.00056 18 0.67197 0.42371 4.45132 Male1.75 7 0.40005 0.05715 0.00030

Fem2 12 0.82220 0.06852 0.00055 18 0.88769 0.35930 4.45132 Male2 7 0.40998 0.05857 0.00038

Fem2.25 12 0.83502 0.06959 0.00045 18 0.72750 0.40555 4.45132 Male2.25 7 0.42886 0.06127 0.00037

Fem2.5 12 0.87157 0.07263 0.00055 18 0.56655 0.46193 4.45132 Male2.5 7 0.45361 0.06480 0.00035

Fem2.75 12 0.90650 0.07554 0.00066 18 0.45086 0.51095 4.45132 Male2.75 7 0.47543 0.06792 0.00040

Fem3 12 0.96391 0.08033 0.00079 18 0.48237 0.49673 4.45132 Male3 7 0.50364 0.07195 0.00038

Fem3.25 12 0.98693 0.08224 0.00077 18 0.35894 0.55700 4.45132 Male3.25 7 0.52444 0.07492 0.00045

Fem3.5 12 0.99102 0.08258 0.00077 18 0.10421 0.75077 4.45132 Male3.5 7 0.55116 0.07874 0.00036

Fem3.75 12 0.99497 0.08291 0.00076 18 0.00122 0.97255 4.45132 Male3.75 7 0.58346 0.08335 0.00056

Fem4 11 0.96493 0.08772 0.00105 17 0.00759 0.93165 4.49400 Male4 7 0.60549 0.08650 0.00049

Fem4.25 11 0.99639 0.09058 0.00160 17 0.01481 0.90465 4.49400 Male4.25 7 0.62049 0.08864 0.00023

Fem4.5 11 1.03343 0.09395 0.00110 17 0.02856 0.86793 4.49400 Male4.5 7 0.64057 0.09151 0.00053

Fem4.75 9 0.84098 0.09344 0.00102 15 0.16922 0.68703 4.60011 Male4.75 7 0.61062 0.08723 0.00073

Fem5 6 0.61787 0.10298 0.00078 10 0.43608 0.52556 5.11736 Male5 5 0.45363 0.09073 0.00114

Fem5.25 5 0.47264 0.09453 0.00071 9 0.43560 0.52779 5.31764 Male5.25 5 0.42005 0.08401 0.00056

340

Table C.10 Results of Single Factor ANOVAs comparing Historical children

and adults (Sr/Ca at 0.25 year intervals)

Historical Children and Adults


Kids 0.5 2 0.08834 0.04417 0.00012 5 0.70560 0.44818 7.70865 Ads0.5 4 0.13081 0.03270 0.00029

Kids 0.75 4 0.15685 0.03921 0.00031 14 0.25278 0.62353 4.66719 Ads0.75 11 0.50077 0.04552 0.00051

Kids 1 9 0.42220 0.04691 0.00023 28 0.00377 0.95148 4.21001 Ads1 20 0.92937 0.04647 0.00036

Kids 1.25 9 0.45277 0.05031 0.00042 33 0.04976 0.82490 4.14909 Ads1.25 25 1.21257 0.04850 0.00044

Kids 1.5 9 0.47784 0.05309 0.00051 33 0.26645 0.60927 4.14909 Ads1.5 25 1.22192 0.04888 0.00042

Kids 1.75 9 0.48534 0.05393 0.00055 33 0.15423 0.69713 4.14909 Ads1.75 25 1.26390 0.05056 0.00047

Kids 2 9 0.48725 0.05414 0.00047 33 0.07166 0.79066 4.14909 Ads2 25 1.29715 0.05189 0.00047

Kids 2.25 9 0.49945 0.05549 0.00037 33 0.05010 0.82432 4.14909 Ads2.25 25 1.34172 0.05367 0.00046

Kids 2.5 9 0.51406 0.05712 0.00043 33 0.04641 0.83079 4.14909 Ads2.5 25 1.38267 0.05531 0.00048

Kids 2.75 9 0.52248 0.05805 0.00049 33 0.00741 0.93195 4.14909 Ads2.75 25 1.43209 0.05728 0.00054

Kids 3 9 0.52691 0.05855 0.00051 33 0.03772 0.84722 4.14909 Ads3 25 1.51049 0.06042 0.00065

Kids 3.25 9 0.54858 0.06095 0.00052 33 0.00381 0.95118 4.14909 Ads3.25 25 1.54020 0.06161 0.00082

Kids 3.5 9 0.58571 0.06508 0.00060 33 0.03528 0.85219 4.14909 Ads3.5 25 1.57552 0.06302 0.00086

Kids 3.75 9 0.62978 0.06998 0.00068 33 0.26277 0.61175 4.14909 Ads3.75 25 1.60799 0.06432 0.00085

Kids 4 9 0.67403 0.07489 0.00080 33 0.76154 0.38935 4.14909 Ads4 25 1.64150 0.06566 0.00072

Kids 4.25 9 0.67580 0.07509 0.00078 33 1.05428 0.31222 4.14909 Ads4.25 25 1.62540 0.06502 0.00059

Kids 4.5 9 0.69170 0.07686 0.00087 33 0.82536 0.37041 4.14909 Ads4.5 25 1.67280 0.06691 0.00077

Kids 4.75 9 0.69766 0.07752 0.00078 26 0.74953 0.39486 4.24170 Ads4.75 18 1.19914 0.06662 0.00103

Kids 5 5 0.39210 0.07842 0.00023 15 0.22539 0.64229 4.60011 Ads5 11 0.76260 0.06933 0.00167

Kids 5.25 4 0.31256 0.07814 0.00031 11 0.02911 0.86793 4.96459 Ads5.25 8 0.59250 0.07406 0.00204

341

Table C.11 Results of Single Factor ANOVAs comparing Historical females

and males (Sr/Ca at 0.25 year intervals)

Historical Females and Males


Fem0.75 6 0.20677 0.03446 0.00024 10 4.18371 0.07114 5.11736

Male0.75 5 0.29401 0.05880 0.00057

Fem1 8 0.34199 0.04275 0.00043 19 0.49835 0.48926 4.41386 Male1 12 0.58739 0.04895 0.00033

Fem1.25 13 0.58623 0.04509 0.00049 24 0.71174 0.40756 4.27934 Male1.25 12 0.62634 0.05220 0.00039

Fem1.5 13 0.58174 0.04475 0.00045 24 1.10439 0.30422 4.27934 Male1.5 12 0.64018 0.05335 0.00039

Fem1.75 13 0.60493 0.04653 0.00053 24 0.93576 0.34343 4.27934 Male1.75 12 0.65897 0.05491 0.00040

Fem2 13 0.64215 0.04940 0.00061 24 0.34790 0.56105 4.27934 Male2 12 0.65500 0.05458 0.00035

Fem2.25 13 0.64362 0.04951 0.00055 24 1.01163 0.32498 4.27934 Male2.25 12 0.69810 0.05818 0.00036

Fem2.5 13 0.67428 0.05187 0.00055 24 0.65850 0.42541 4.27934 Male2.5 12 0.70839 0.05903 0.00041

Fem2.75 13 0.70098 0.05392 0.00061 24 0.55458 0.46400 4.27934 Male2.75 12 0.73111 0.06093 0.00049

Fem3 13 0.74855 0.05758 0.00083 24 0.32557 0.57381 4.27934 Male3 12 0.76193 0.06349 0.00050

Fem3.25 13 0.77394 0.05953 0.00111 24 0.13688 0.71478 4.27934 Male3.25 12 0.76626 0.06386 0.00057

Fem3.5 13 0.78107 0.06008 0.00120 24 0.26361 0.61255 4.27934 Male3.5 12 0.79445 0.06620 0.00055

Fem3.75 13 0.82460 0.06343 0.00127 24 0.02418 0.87777 4.27934 Male3.75 12 0.78339 0.06528 0.00046

Fem4 13 0.84387 0.06491 0.00114 24 0.02013 0.88840 4.27934 Male4 12 0.79763 0.06647 0.00033

Fem4.25 13 0.81894 0.06300 0.00088 24 0.18078 0.67465 4.27934 Male4.25 12 0.80646 0.06721 0.00031

Fem4.5 13 0.83177 0.06398 0.00109 24 0.29363 0.59311 4.27934 Male4.5 12 0.84103 0.07009 0.00047

Fem4.75 10 0.68550 0.06855 0.00134 17 0.07696 0.78501 4.49400 Male4.75 8 0.51364 0.06421 0.00077

Fem5 6 0.44710 0.07452 0.00219 10 0.19533 0.66895 5.11736 Male5 5 0.31550 0.06310 0.00135

Fem5.25 5 0.36461 0.07292 0.00186 7 0.00728 0.93477 5.98737 Male5.25 3 0.22789 0.07596 0.00341

342

Table C.12 Results of Single Factor ANOVAs comparing Postclassic and Historical

children (Sr/Ca at 0.25 year intervals)

Postclassic and Historical Children


N10 0.5 2 0.09034 0.04517 0.00005 3 0.01122 0.92531 18.51276 YDL 0.5 2 0.08834 0.04417 0.00012

N10 0.75 4 0.20988 0.05247 0.00030 7 1.15284 0.32423 5.98737 YDL 0.75 4 0.15685 0.03921 0.00031

N10 1 6 0.29717 0.04953 0.00029 14 0.09634 0.76118 4.66719 YDL 1 9 0.42220 0.04691 0.00023

N10 1.25 6 0.30785 0.05131 0.00037 14 0.00898 0.92594 4.66719 YDL 1.25 9 0.45277 0.05031 0.00042

N10 1.5 6 0.29658 0.04943 0.00026 14 0.11738 0.73737 4.66719 YDL 1.5 9 0.47784 0.05309 0.00051

N10 1.75 6 0.30671 0.05112 0.00028 14 0.06351 0.80497 4.66719 YDL 1.75 9 0.48534 0.05393 0.00055

N10 2 6 0.32747 0.05458 0.00033 14 0.00167 0.96798 4.66719 YDL 2 9 0.48725 0.05414 0.00047

N10 2.25 6 0.34680 0.05780 0.00038 14 0.05124 0.82444 4.66719 YDL 2.25 9 0.49945 0.05549 0.00037

N10 2.5 6 0.34065 0.05677 0.00035 14 0.00106 0.97456 4.66719 YDL 2.5 9 0.51406 0.05712 0.00043

N10 2.75 6 0.37256 0.06209 0.00079 14 0.09678 0.76066 4.66719 YDL 2.75 9 0.52248 0.05805 0.00049

N10 3 6 0.37283 0.06214 0.00048 14 0.09344 0.76469 4.66719 YDL 3 9 0.52691 0.05855 0.00051

N10 3.25 6 0.39215 0.06536 0.00045 14 0.14263 0.71177 4.66719 YDL 3.25 9 0.54858 0.06095 0.00052

N10 3.5 6 0.40421 0.06737 0.00032 14 0.03841 0.84765 4.66719 YDL 3.5 9 0.58571 0.06508 0.00060

N10 3.75 6 0.41496 0.06916 0.00035 14 0.00433 0.94853 4.66719 YDL 3.75 9 0.62978 0.06998 0.00068

N10 4 6 0.43063 0.07177 0.00047 14 0.05192 0.82330 4.66719 YDL 4 9 0.67403 0.07489 0.00080

N10 4.25 6 0.43395 0.07233 0.00042 14 0.04310 0.83876 4.66719 YDL 4.25 9 0.67580 0.07509 0.00078

N10 4.5 6 0.42925 0.07154 0.00044 14 0.14477 0.70973 4.66719 YDL 4.5 9 0.69170 0.07686 0.00087

N10 4.75 4 0.30462 0.07615 0.00055 12 0.00716 0.93408 4.84434 YDL 4.75 9 0.69766 0.07752 0.00078

N10 5 2 0.16001 0.08001 0.00050 6 0.01267 0.91475 6.60788 YDL 5 5 0.39210 0.07842 0.00023

N10 5.25 3 0.25276 0.08425 0.00081 6 0.12529 0.73780 6.60788 YDL 5.25 4 0.31256 0.07814 0.00031

343


females (Sr/Ca at 0.25 year intervals)

(* denotes significant difference)

Postclassic and Historical Females


N10 0.5 2 0.14623 0.07312 0.00005 5 9.48862 *0.03692 7.70865 YDL 0.5 4 0.13081 0.03270 0.00029

N10 0.75 5 0.33568 0.06714 0.00044 10 8.84065 *0.01562 5.11736 YDL 0.75 6 0.20677 0.03446 0.00024

N10 1 9 0.55501 0.06167 0.00048 16 3.30189 0.08923 4.54307 YDL 1 8 0.34199 0.04275 0.00043

N10 1.25 11 0.68828 0.06257 0.00049 23 3.73040 0.06641 4.30094 YDL 1.25 13 0.58623 0.04509 0.00049

N10 1.5 12 0.76424 0.06369 0.00052 24 4.65515 *0.04164 4.27934 YDL 1.5 13 0.58174 0.04475 0.00045

N10 1.75 12 0.78660 0.06555 0.00056 24 4.14578 0.05341 4.27934 YDL 1.75 13 0.60493 0.04653 0.00053

N10 2 12 0.82220 0.06852 0.00055 24 3.92022 0.05980 4.27934 YDL 2 13 0.64215 0.04940 0.00061

N10 2.25 12 0.83502 0.06959 0.00045 24 4.98177 *0.03564 4.27934 YDL 2.25 13 0.64362 0.04951 0.00055

N10 2.5 12 0.87157 0.07263 0.00055 24 4.89554 *0.03713 4.27934 YDL 2.5 13 0.67428 0.05187 0.00055

N10 2.75 12 0.90650 0.07554 0.00066 24 4.57797 *0.04322 4.27934 YDL 2.75 13 0.70098 0.05392 0.00061

N10 3 12 0.96391 0.08033 0.00079 24 4.00118 0.05741 4.27934 YDL 3 13 0.74855 0.05758 0.00083

N10 3.25 12 0.98693 0.08224 0.00077 24 3.39603 0.07828 4.27934 YDL 3.25 13 0.77394 0.05953 0.00111

N10 3.5 12 0.99102 0.08258 0.00077 24 3.17937 0.08778 4.27934 YDL 3.5 13 0.78107 0.06008 0.00120

N10 3.75 12 0.99497 0.08291 0.00076 24 2.30252 0.14279 4.27934 YDL 3.75 13 0.82460 0.06343 0.00127

N10 4 11 0.96493 0.08772 0.00105 23 2.82204 0.10713 4.30094 YDL 4 13 0.84387 0.06491 0.00114

N10 4.25 11 0.99639 0.09058 0.00160 23 3.75095 0.06573 4.30094 YDL 4.25 13 0.81894 0.06300 0.00088

N10 4.5 11 1.03343 0.09395 0.00110 23 4.88964 *0.03771 4.30094 YDL 4.5 13 0.83177 0.06398 0.00109

N10 4.75 9 0.84098 0.09344 0.00102 18 2.46219 0.13504 4.45132 YDL 4.75 10 0.68550 0.06855 0.00134

N10 5 6 0.61787 0.10298 0.00078 11 1.63537 0.22984 4.96459 YDL 5 6 0.44710 0.07452 0.00219

N10 5.25 5 0.47264 0.09453 0.00071 9 0.90683 0.36884 5.31764 YDL 5.25 5 0.36461 0.07292 0.00186

344


males (Sr/Ca at 0.25 year intervals)

(* denotes significant difference)

Postclassic and Historical Males


N10 0.75 1 0.03870 0.03870 N/A 5 0.59267 0.48433 7.70865 YDL 0.75 5 0.29401 0.05880 0.00057

N10 1 5 0.27851 0.05570 0.00044 16 0.44552 0.51461 4.54307 YDL 1 12 0.58739 0.04895 0.00033

N10 1.25 7 0.35565 0.05081 0.00028 18 0.02406 0.87855 4.45132 YDL 1.25 12 0.62634 0.05220 0.00039

N10 1.5 7 0.37733 0.05390 0.00034 18 0.00368 0.95235 4.45132 YDL 1.5 12 0.64018 0.05335 0.00039

N10 1.75 7 0.40005 0.05715 0.00030 18 0.06110 0.80773 4.45132 YDL 1.75 12 0.65897 0.05491 0.00040

N10 2 7 0.40998 0.05857 0.00038 18 0.19576 0.66374 4.45132 YDL 2 12 0.65500 0.05458 0.00035

N10 2.25 7 0.42886 0.06127 0.00037 18 0.11595 0.73764 4.45132 YDL 2.25 12 0.69810 0.05818 0.00036

N10 2.5 7 0.45361 0.06480 0.00035 18 0.37445 0.54869 4.45132 YDL 2.5 12 0.70839 0.05903 0.00041

N10 2.75 7 0.47543 0.06792 0.00040 18 0.47558 0.49974 4.45132 YDL 2.75 12 0.73111 0.06093 0.00049

N10 3 7 0.50364 0.07195 0.00038 18 0.68924 0.41793 4.45132 YDL 3 12 0.76193 0.06349 0.00050

N10 3.25 7 0.52444 0.07492 0.00045 18 1.02062 0.32654 4.45132 YDL 3.25 12 0.76626 0.06386 0.00057

N10 3.5 7 0.55116 0.07874 0.00036 18 1.43544 0.24732 4.45132 YDL 3.5 12 0.79445 0.06620 0.00055

N10 3.75 7 0.58346 0.08335 0.00056 18 2.90750 0.10637 4.45132 YDL 3.75 12 0.78339 0.06528 0.00046

N10 4 7 0.60549 0.08650 0.00049 18 4.59187 *0.04689 4.45132 YDL 4 12 0.79763 0.06647 0.00033

N10 4.25 7 0.62049 0.08864 0.00023 18 7.10591 *0.01630 4.45132 YDL 4.25

12 0.80646 0.06721 0.00031

N10 4.5 7 0.64057 0.09151 0.00053 18 4.11598 0.05844 4.45132 YDL 4.5 12 0.84103 0.07009 0.00047

N10 4.75 7 0.61062 0.08723 0.00073 14 2.64189 0.12807 4.66719 YDL 4.75 8 0.51364 0.06421 0.00077

N10 5 5 0.45363 0.09073 0.00114 9 1.53145 0.25098 5.31764 YDL 5 5 0.31550 0.06310 0.00135

N10 5.25 5 0.42005 0.08401 0.00056 7 0.08040 0.78628 5.98737 YDL 5.25 3 0.22789 0.07596 0.00341

345

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