Fragmentation Resistant Measures of Chipped Stone Abundance and Size: Results of an Experimental...

353

Matthew Douglass and LuAnn Wandsnider Cattle Trampling Impacts on Chipped Stone

Plains Anthropologist, Vol. 57, No. 224, pp. 353–365, 2012

Fragmentation Resistant Measures of Chipped StoneAbundance and Size: Results of an Experimental

Investigation of the Impact of Cattle Trampling onSurface Chipped Stone Scatters

Matthew Douglass and LuAnn WandsniderThis study reports on the execution of a controlled experiment designed to address the impacts of

cattle trampling on surface scatters of chipped stone found in Great Plains contexts. A key focus of theexperiment’s design is an evaluation of the relationship between trampling duration and substratecompaction on the severity of artifact breakage. Results indicate that post-depositional artifact frag-mentation can significantly distort common analytical approaches found within the archaeologicalliterature. Namely, measures of artifact abundance, raw material proportions, and average artifactdimensions are all affected by the impacts of trampling fragmentation. Beyond a consideration of keyvariables in the process of trampling fragmentation and its effects on analysis, this study outlinesanalytical means to identify and control for this bias. Tell-tale indicators of trampling damage aredescribed and prescriptive measures designed to mitigate against the effects of trampling are evaluated.Results indicate that if dealt with appropriately, fragmented assemblages should not to be dismissed asdistorted beyond usefulness, but instead can be utilized to reveal latent information about past humanbehavior.

Keywords: lithic technology, taphonomy

Matthew Douglass, Department of Anthropology, University of Nebraska, 810 Oldfather Hall, P.O. Box880368, Lincoln, NE 68588-0368, [email protected]

LuAnn Wandsnider, Department of Anthropology, University of Nebraska, 810 Oldfather Hall, P.O. Box880368, Lincoln, NE 68588-0368

Recent exploration of chipped stone artifactswithin surface deposits in the Oglala National Grass-lands and Nebraska National Forest (Wandsnideret al. 2008) has brought the effects of taphonomyinto sharp focus. Identified scatters have conspicu-ously high amounts of artifact fragmentation and itis our suspicion that much of the fragmentationmay be associated with cattle that frequent theseareas. Indeed, on several occasions we have wit-nessed cattle trampling artifact scatters we havestudied.

The potential impact of trampling to surface

chipped stone assemblages is of considerable con-cern given that such assemblages often representthe primary information we have about past use ofsemi-arid areas like the Great Plains. Owing to densegrass cover, small windows of visibility (e.g., blowouts, wallows, animal burrows, livestock trails, andpaths and roadways) play a primary role as units ofdiscovery and analysis in many Plains contexts.The limited scale and thus limited size of the lithicassemblages documented for these features makesthem particularly susceptible to sources of databias and it is often an evaluation of such remains

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PLAINS ANTHROPOLOGIST VOL. 57, NO. 224, 2012

upon which decisions about subsurface testing andmanagement are predicated.

This study, therefore, has two goals. The firstis to experimentally evaluate the impacts of tram-pling fragmentation on the formal characteristicsof surface scatters of chipped stone. In particular,this study evaluates the relationship between arti-fact breakage, trampling duration, and substratecompaction and how this process affects descrip-tive measures commonly reported within the ar-chaeological literature. Results confirm that cattletrampling does indeed cause significant fragmen-tation to lithic remains, and that this can poten-tially bias archaeological interpretation. In particu-lar, we find that the impacts of trampling can greatlycomplicate interpretations of artifact abundance,raw material proportions, and average artifact di-mensions, especially when samples are small. Asecond goal is to explore the analytic means tocorrect or control for the effects of trampling. Weevaluate two measures that have been proposedas resistant to the biasing effects of trampling.

BACKGROUNDPrevious research has examined the effects of

trampling (both human and animal) on replicatedlithic assemblages. The results conclude that bothforms of trampling can produce damage that in manyways mimics deliberate retouch (Flenniken andHaggerty 1979; Gifford-Gonzalez et al. 1985;Knudson 1979; Lopinott and Ray 2007; McBreartyet al. 1998; Tringham et al. 1974), removes traces ofuse-wear (Shea and Klenck 1993), and increasesamounts of artifact breakage (Boot 1987; Osborn etal. 1987; Roney 1977). The effects of trampling dam-age can subsequently affect measures of flake com-pleteness, the proportion of flakes with dorsal cor-tex, and average flake size (Rasic 2004: 132). Fur-thermore, the severity of this modification is owedto a combination of substrate variability and tram-pling time (McBrearty et. al 1998; Nielsen 1991; Pryor1988).

Pryor’s (1988) study is of particular importanceto the experiment reported here. In evaluating theeffects of human trampling, Pryor noted the impor-tance of substrate as a variable influencing the in-teraction between artifacts and trampling. In whathe termed the “Soil Penetrability Loop,” Pryor con-cluded that the degree of penetrability for a given

substrate greatly influenced the overall severity oftrampling damage. He asserted that artifact dam-age on harder, more compact surfaces would begreater than that found on surfaces that were softerand less compact. According to Pryor, this was aresult of substrate penetrability, where softer sedi-ments, with their tendency to cover artifacts, actedto reduce contact between artifacts and the agentof trampling, a finding similar to that of Gifford-Gonzalez et al. (1985).

The study reported here expands animal tram-pling studies in a number of important ways. Thecontrolled nature of the study allows a clear pic-ture of the trampling process in staged intervalswhile expanding understanding of the relationshipbetween sediment compaction and trampling dura-tion on the formation of artifact damage. Beyond ademonstration and evaluation of potential impacts,this study offers an important consideration of theeffect this phenomenon has on interpretation ofpast human behavior. Our focus is specifically de-signed to address a common predicament faced byresearchers in the Plains; how to analyze surfacescatters of chipped stone where high rates of arti-fact breakage point to the effects of post-deposi-tional fragmentation. This issue is not unique tothe Plains, but is also a pervasive problem faced inmany regions of the world where livestock or wildherbivores come in contact with the surface ar-chaeological record. To aid researchers faced withthis situation, we describe a number of commontell-tale signs of trampling damage and outline ananalytical approach for diminishing the biasing ef-fects these impacts have on common measures re-ported in the archaeological literature.

RESEARCH DESIGN AND METHODSIn order to evaluate the effect of cattle tram-

pling on chipped stone, we designed and executeda controlled experiment in which scatters of experi-mentally replicated flakes, situated on substratesvarying in penetrability or consolidation, were trod-den on for varying intervals of time. The experi-ment was completed within a fenced cattle lot atthe Hammons Family Farm in Weeping Water, Ne-braska. The lot had a clayey-loam substrate withroughly level ground and the surface was free ofvegetation and obstructing stones.

Three different experimental stations with dif-

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fering degrees of substrate compaction were se-lected for monitoring the effects of trampling. Tenreadings of substrate compaction, measured inpounds per square inch (psi) with a Lange Pen-etrometer, were averaged for each station yieldinga mean measure of substrate compaction. Scatter 1was placed on a loose, unconsolidated surface withan average compaction of 230 psi. Scatter 2 had amoderately consolidated surface with a mean com-paction of 370 psi, and Scatter 3 was placed on anindurated surface with a substrate compaction of710 psi.

A two-part enclosure constructed of cattlefence was erected to surround the three experimen-tal scatters (Figure 1). The main component of theenclosure consisted of a roughly 2-m wide “alley”that ran a course along all three scatters. The sec-ond part of the enclosure was a small holding penwhere the cattle were kept between tramplingevents. Gates leading into the holding pen wereplaced at either end of the alley forming a continu-ous circuit. Within each scatter location, flakes wereplaced within a 1-x-1- m square, with approximately3 cm between each specimen.

Experimental MaterialsThe experimental assemblages consisted of

213 flakes and flake fragments produced by a vari-ety of different reduction strategies by local flint-knappers. Maximum dimensions weremeasured for all specimens, which werethen ordered into three approximatelyequal groupings and assigned to oneof three experimental assemblages.Each assemblage was composed of 34novaculite specimens and 37 obsidianspecimens.

A coding system based on over-lapping coats of spray paint was de-veloped in order to provide a fractureresistant form of artifact identificationas well as to facilitate the location ofany damage caused through trampling.In this system, each artifact received abase coat on both its dorsal and ven-tral surfaces with one color of spraypaint, and an outer coating on its dor-sal surface with a different color. Eachof the 10 paint colors was assigned a

number from zero to nine and each raw materialtype was assigned a number from one to four (ob-sidian was separated into three categories basedon color). The combination of an artifact’s spraypaint coatings and its material type thus produceda unique three digit identification: stone raw mate-rial types (hundreds); outer paint coating (tens);inner paint coating (ones). This three digit numberwas then written on each flake to assist in the rapididentification of specimens that remained unalteredbetween trampling events.

With this system, an account of new damagecould be recorded for every artifact (and fragmentsthereof) at the end of each interval in theexperiment’s operation (see below). This facilitateda detailed understanding of the relationship be-tween trampling duration and the formation of dam-age for individual artifacts, while simultaneouslydiminishing the chance of observer error as addi-tional measurements were not needed unless a flakereceived new damage.

Experimental ProcedureThe experiment consisted of three separate

trampling events. In Event 1, 20 individual cattlepasses were completed over each of the experi-mental scatters (i.e., one cow walked over each scat-ter 20 times). In Event 2, 40 passes were completedfor a combined total for the first two events of 60

Figure 1. Schematic representation of the experimental cattle enclosure:(a) enclosure gates were opened to create a circuit where cattle were herdedover the experimental scatters; (b) after each trampling event, the gateswere closed. The cattle remained in a holding pen while the experimentalscatters were analyzed.

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cattle passes. Eighty passes were completed inEvent 3, for a total of 140 cattle passes at the con-clusion of the trampling experiment.

Each event proceeded in the following man-ner. The gates to the holding pen were opened cre-ating a continuous circuit around which the cattlecould be driven. Five cattle were then herded intothe alley so that they could pass over all three scat-ters, and then walk back into the pen from the otherside. This process continued until the desired num-ber of passes had been completed. At the conclu-sion of each event, the gates were closed and thecattle were once again held within the holding pen.Each experimental artifact was then located, ana-lyzed, and returned to the location from which itwas found. Table 1 provides summary data of theexperimental assemblages by event. The variable“snap” refers to any artifact damage equal to orgreater than 1 cm in the maximum dimension.

RESULTSThe results of this study confirm that tram-

pling fragmentation can be extensive, even afterencounters with the hooves of 20 cattle, and thatvariation in substrate compaction affects the se-verity of this breakage (Table 1). Assemblage char-acteristics after 140 cattle passes illustrate the ex-tent of this impact: Scatter 1 (230 psi) shows theleast impact with .56 snaps per specimen, followedby Scatter 2 (370 psi) with .84 snaps per specimen,and Scatter 3 (710 psi) with 1.09 snaps per speci-men. Mean artifact dimensions for each scatter dem-onstrate a similar relationship. Again from less com-pact to more compact substrate, Scatter 1 sufferedthe smallest reduction (-20.9 percent) in artifactlength (maximum dimension) followed by Scatter 2(-24.8 percent) and Scatter 3 (-31.1 percent). Thesefindings confirm that substrate compaction plays asignificant role in the degree of artifact fragmenta-tion as a result of trampling.

Data from each of the three events make it pos-sible to monitor alterations to the three scatters asthe experiment proceeded (Table 1), allowing anexamination of the relationship between tramplingduration and the severity of trampling damage. Fig-ure 2 depicts the average artifact snap frequencyand average artifact length for each scatter througheach trampling event. This representation of thedata clearly illustrates that artifact breakage in-

creases with continued trampling and, concomi-tantly, mean artifact dimension decreases.

The trends noted for snap frequency and meanspecimen length are not found to be directly pro-portional to the number of cattle passes. Instead,there is a general decrease in the rate with whichalteration occurs as trampling time increases. As aresult, the variables “impact fractures per 20passes” and “mean length reduction per artifactper 20 cattle passes” (measured in mm) were cre-ated to monitor this trend.

The impact fracture variable measures new frac-tures rather than the number of broken edges (mea-sured by the snap variable), and thus provides aclearer indication of the rate of fragmentation. Forinstance, splitting a flake into two separate frag-ments produced two snaps, while a fracture alonga flake’s margin would result in only one snap. Inthe new variable, one new fracture would be re-corded in each of these cases. Furthermore, thisvariable refers only to new damage that occurredduring each trampling event rather than the cumu-lative variable snaps. Finally, in order to make di-rect comparisons of the amount of damage incurredthrough time, the new variable is standardized by20 passes. The mean length reduction per artifactvariable reflects a similar conversion used to moni-tor the decrease in artifact size as measured bymaximum flake dimensions. This variable is alsostandardized by 20 cattle passes.

A graph representation of the new variables(Figure 3) demonstrates that the number of newimpact fractures decreased from Event 2 to Event 3for each scatter and that mean reduction in lengthat the conclusion of the experiment was lower thanthat noted between Events 1 and 2.

These findings mirror those reported by Pryor(1988). To explain this pattern, he suggests that asflakes decrease in size through edge damage, theyapproach a size equilibrium where they become re-sistant to further breakage given substrate com-paction. The results presented here support thisassertion, though this equilibrium had yet to bereached at the conclusion of 140 cattle passes.

Other FindingsThere are a number of peculiar findings that

are at odds with the relationship assumed to existbetween trampling damage, substrate compaction,

357

Matthew Douglass and LuAnn Wandsnider Cattle Trampling Impacts on Chipped StoneTa

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and trampling duration. First, Event 1 data (Figure3b) show higher rates of fragmentation and reduc-tion in flake length for Scatter 1 than for the morecompact Scatter 2. This pattern continues intoEvent 2 for rates of fragmentation. This observa-tion deviates from the assumed positive relation-ship between substrate compaction and the sever-ity of trampling damage. Additionally, there is anincrease in the rate of fragmentation and loss inartifact length from Event 1 to Event 2 for bothScatter 1 and Scatter 2, a finding that is opposite tothe notion that rates of fragmentation should de-crease as trampling time progresses.

A possible explanation for the discrepancy inthe relationship between compaction and tramplingdamage may relate to differences in substrate tex-

ture between the twoscatters. The loose sub-strate at Scatter 1 re-sulted in vertical dis-placement as artifactswere pushed downward.This effect contributedto greater amounts offlake overlap as someflakes became bunchedtogether in the initialstages of the experiment,and may explain thegreater rates of fragmen-tation. In a similar find-ing, McBrearty et al.(1998) noted the effectsof “artifact on artifact”impacts as a significantsource of artifact damagein experiments involvinghuman treadage. As tram-pling progressed, how-ever, the loosely com-pacted substrate forScatter 1 also served todecrease artifact move-ment, so additionalstacking was reduced asthe experiment pro-ceeded.

This explanationdoes not, however, ac-

count for the increase in snap frequency per cattlepass noted for Event 2 in each of these two scat-ters (Figure 3a). This occurrence could potentiallybe the result of two factors. First, the cushioningeffect of a substrate is probably greatest duringthe initial impacts of trampling. This is because tram-pling is likely to create a slight increase in sub-strate compaction immediately following compres-sion (Liddle 1997). Such an effect would not havebeen likely for the more indurated Scatter 3, thusexplaining the absence of an increase in snaps dur-ing Event 2 for this scatter. A second explanation isperhaps owed to the cattle themselves. As the cattlebecame more accustomed to the task that was askedof them, they were more likely to complete the en-tire circuit without stopping and the general speed

Figure 2. Graphic illustration of experimental trampling damage: (a) mean snaps by scatterand event; (b) mean artifact length by scatter and event. Artifact length measurement inmm.

Figure 3. Graphic illustration of two variables: (a) impact fractures per 20 cattle passes byevent; (b) mean reduction in length (mm) per artifact for every 20 cattle passes

359


with which they moved through the enclosure in-creased slightly. This learning process on the partof the cattle is likely to have resulted in a slightincrease in trampling intensity, and could in part beresponsible for the increase in fragmentation fromEvent 1 to Event 2.

These three factors are likely to have resultedin the unusual findings noted for Scatters 1 and 2.The general trend noted by Pryor (1988) in whichthe rate of subsequent damage is likely to decreasewith increased trampling duration, would appear tostill hold for this experiment. The rates of fragmen-tation noted for Event 3, however, suggest that theexperimental scatters may have still been vulner-able to additional trampling damage even after 140cattle passes had been completed.

IMPLICATIONSThe analysis presented here confirms that the

modification of chipped stone assemblages as aresult of cattle trampling is far from negligible. Tram-pling causes severe fragmentation and diminishedartifact size irrespective of substrate compactionand trampling duration. The near ubiquity of cattle(and other sources of impact fragmentation) withinPlains contexts means that impacts are likely wide-spread and likely influence interpretation. The fol-lowing outlines a number of meaningful avenueswith which researchers can identify the presenceof trampling damage and mitigate its effects oninterpretation.

Identification of Trampling DamageBeyond the frequency of artifact breakage,

there are a number of diagnostic traces that arefound on chipped stone artifacts that have beentrampled. A major set of marks are the scuffage,striations, and abrasion tracks that form along aflake’s surface (e.g., Shea and Klenck1993: Fig-ure 8) as a result of artifacts being pushed downagainst the substrate during trampling. Severalresearchers have noted such wear in assem-blages subject to human trampling in both ex-perimental (Bordes 1961; McBrearty et al.1998)and archaeological contexts (Shea and Klenck1993). The results of this experiment indicatethat scuffage is also indicative of cattle tram-pling, having been readily identified on experi-mental artifacts from all substrate compactions.

Trampling also propagates small flake removals—mimicking retouch—that are found along flakeedges and on dorsal ridges. This retouch can beexceedingly small and results in the general blunt-ing of flake edges and dorsal ridges. The fact thatthese breaks also occur on dorsal ridges and areseldom continuous on flake edges makes them atell-tale sign of post-depositional breakage, a con-clusion drawn in other investigations (McBreartyet al. 1998; Odell and Cowan 1987). A final identifiercomes in the form of unique crescent-shaped break-age along flake margins (Figure 4). The unique arch-ing shape of these breaks is unlikely to be createdduring reduction, and is perhaps owed to the shapeand hardness of the trampler’s hooves.

Effects on InterpretationIn order to address the effects of trampling

damage on the interpretation of lithic assemblagepatterning, we now turn to an evaluation of thecharacteristics of the three experimental assem-blages as they changed throughout the experiment.The similarity in assemblage composition (Table 1)is of great value in its ability to shed light on anappropriate methodology for mitigating the effectsof prolonged trampling. By monitoring the effec-tiveness of a variety of common analytical proce-dures, these data comment on the most appropri-ate analytic techniques.

Assemblage SizeEven the most basic of lithic analyses includes

Figure 4. Crescent-shaped fragmentation.

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an estimate of artifact abundance. It is this estimatethat forms the basis from which are derived sum-mary measures such as relative raw material fre-quencies, tool proportions, and artifact density.Within the discipline, however, there is no one pre-ferred technique for such descriptions, and more-over, not all techniques are robust enough to notbe heavily affected by taphonomic processes.

The simplest approach is to report the fre-quency of all lithic artifacts within an assemblageregardless of completeness. The result is a descrip-tion of the number of artifactual specimens (NAS),which is an equivalent to the number of individualspecimens (NISP) used in faunal analysis. An alter-native is to limit estimates only to complete arti-facts, including both unretouched flakes and tools.A number of more complex and seemingly morerobust measures rely on the ordering of flakes andflake fragments into categories based on readilyidentifiable landmarks. One approach relies on theminimum number of impacts (MNI), calculated bycounting all platform-bearing specimens (completeflakes and proximal fragments) within an assem-blage. Because all flakes will contain a point of frac-ture initiation, it is assumed that an inventory ofthe total number of initiations will result in a mea-sure of the total number of flakes withinan assemblage. In practice, however,there are instances in which counts ofcomplete flakes and proximal fragmentswill underestimate true values (e.g.,obliterated platforms and the vagariesof archaeological sampling).

In an effort to avoid this effect,Hiscock (2002) developed an estimatefor the minimum number of flakes(MNF), which includes the use of dis-tal and longitudinal fragments. Longi-tudinal fragment are flake fragmentsthat are formed as a result of fracturealong the axis of percussion duringflake formation (Figure 5). These frag-ments retain both a portion of the plat-form and a portion of the terminationand are divided into split right and splitleft longitudinal portions. These twolongitudinal fragment types can sub-sequently be transversely fracturedinto proximal and distal portions, thus

adding additional variability to the entire suite offragment types. The computation of MNF is orga-nized into the equation:

MNF = C + T + L,where C represents the number of complete flakes;T represents the greater of either proximal or distalfragments; and, L is the sum of the greater of eitherleft or right complete longitudinal fragments plusthe greater of the four transversely fractured longi-tudinal fragments.

MNF was measured in this experiment, how-ever, with modification so as to include an addi-tional flake fragment type not recorded in Hiscock’staxonomy. This fragment type retains the fractureinitiation along with either the right or left intersec-tion of the flake termination and lateral margin andis labeled proximal distal left (PDL) or proximal dis-tal right (PDR; Figure 5). This fragment type is adirect result of trampling damage where a portionof the flake termination has been snapped off. Theapplication of MNF presented here allows thesefragments to be counted as either proximal frag-ments or distal portions within the MNF equation.

Results from the experiment, presented in Table2, show the effects of trampling on the variousmeasures of artifact frequency. The instability of

Figure 5. Fragment taxonomy utilized in generating MNI (minimum num-ber of impacts) and MNF (minimum number of flakes) estimates.

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nB

lack

Obs

idia

nR

ed O

bsid

ian

Nov

acul

iteTo

tal

EVEN

T0

12

30

12

30

12

30

12

30

12

3Ex

perim

enta

l Sca

tter 1

NA

S21

2126

289

1016

167

910

1034

3538

4271

7590

96M

NI

1717

1615

87

77

55

55

2828

2828

5857

5655

MN

F21

2121

218

88

86

66

633

3333

3368

6868

68C

ompl

ete

1717

1311

76

44

44

44

2726

2522

5553

4641

Expe

rimen

tal S

catte

r 2N

AS

2121

3336

910

1114

77

910

3437

4050

7175

9311

0M

NI

1616

1616

88

88

66

66

2424

2423

5454

5454

MN

F20

1919

188

88

87

77

730

3030

3065

6464

63C

ompl

ete

1514

97

77

65

66

55

2018

1713

4845

3730

Expe

rimen

tal S

catte

r 3N

AS

2123

4038

914

1722

78

811

3442

4656

7187

111

127

MN

I17

1717

174

44

45

55

521

2121

2147

4747

47M

NF

2020

1919

88

88

66

66

3131

3030

6565

6363

Com

plet

e16

1412

104

22

25

44

319

1713

1244

3731

27N

ote:

Row

-hea

ding

cod

es—

NA

S=nu

mbe

r of a

rtifa

ctua

l spe

cim

ens;

MN

I=m

inim

um n

umbe

r of i

mpa

cts;

MN

F=m

inim

um n

umbe

r of f

lake

s.

362


specimen and complete artifact counts is clearlyindicted. Trampling fragmentation increases totalartifacts and therefore measures of NAS while de-creasing the number of complete specimens. Theseverity of these effects is further influenced bydifferences in substrate compaction. Calculatedmeasures of MNI and the MNF, on the other hand,show stability even through numerous tramplingevents. On average, MNI estimates of abundancedecreased by only 1.89 percent and MNF estimatesdecreased by only 1.99 percent. This would sug-gest that both of these measures provide very stableestimates of assemblage abundance even whenfragmentation is severe. While MNI is easier toestimate, for assemblages in which the ratio of plat-form-bearing specimens to termination-bearingspecimens results in a value less than one, MNFwill provide an estimate that is closer to true as-semblage abundance. Differences between the per-formance of the two estimates become less signifi-cant once assemblage size increases, but are im-portant when samples are small, meaning the addedmeasurements required for an estimate of MNF arelikely justified where limitations in surface expo-sure preclude the analysis of large assemblages.

The variable performance of the different esti-mates of assemblage size also affects interpreta-tion of relative raw material proportions. Becausefiner-grained materials are more prone to fragmen-tation, they are likely to be overrepresented in rela-tion to more durable materials based on artifactcounts alone. Relative raw material proportionsbased on NAS can thus dramatically inflate theperceived utilization of high-quality materials whilematerial proportions based on complete flakeswould have the opposite effect. The stability ofMNI and MNF, therefore, makes them a more ap-propriate measure of relative raw material propor-tions for assemblages affected by fragmentation.

Finally, the different measures of artifact abun-dance can be used to assess the integrity of as-semblage contents. The ratio of NAS to MNF pro-vides a measure of the number of fragments pro-duced for each flake, in effect providing a measureof the potential for fragmentation to bias measuresof artifact composition.

Artifact SizeAnother important measure of assemblage

variability is average artifact size. As noted, suchmeasures are greatly affected by the impacts oftrampling. Several authors have noted the occur-rence of significant amounts of fragmentation withintheir assemblages and have offered means of over-coming bias in estimates of artifact size.

Roth (1995), when analyzing assemblages insouthern Arizona, noted severe breakage, much ofit likely the result of cattle trampling. To gain anestimate of premodification artifact size, she reliedon measurements obtained from the remaining com-plete flakes, but noted the possibility that suchestimates were skewed towards larger size classes.Similarly, Baumler and Speth (1993) reported on aMiddle Paleolithic cave assemblage in Iran in which40 percent of the unretouched flakes were broken.They too relied on the use of complete flake esti-mates for measures of artifact size.

The experimental assemblages provide an op-portunity to test the reliability of this approach.Measurements of length, width, and thickness forcomplete flakes in the experimental assemblagesare presented in Table 3. Results obtained through-out the experiment’s completion indicate that aver-age dimensions do change with increased tram-pling, but they are a considerable improvement overthe dimensions gained from comparisons of allspecimens regardless of completeness (Figure 2b).These findings suggest that descriptions of meanartifact size within chipped stone assemblages thatare measured on complete flakes are in many re-spects resistant to the effects of trampling damage.As a qualification, however, the degree of assem-blage completeness (C:MNF) should be reportedwith these values in instances where fragmenta-tion rates are high along with the caveat that thehigh degree of fragmentation may affect the accu-racy of the results. For instance, of the differentvalues obtained at the completion of the experi-ment, the .25 ratio for black obsidian in Scatter 3 isthe lowest (Table 2). This would suggest that thereis considerable potential for bias to exist in mea-surements of complete flakes for these materials inScatter 3. The .71 value for Scatter 2 red obsidian is,however, the highest proportion recorded for anymaterial within the experimental assemblages (Table2). This would suggest that measurements madeon complete flakes from this material type in Scat-

363


ble

3. D

imen

sion

s of

Com

plet

e Fl

akes

fro

m E

xper

imen

tal S

catte

rs.

Ban

ded

Obs

idia

nB

lack

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idia

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bsid

ian

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acul

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tal

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EN

T0

12

30

12

30

12

30

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30

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men

tal

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ter

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44

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D.

7.2

7.2

5.1

4.6

5.9

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5.9

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9.3

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98.

58.

98.

88.

88.

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ID24

2423

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.530

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77.

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11

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ter

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77

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.937

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.233

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.747

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39.8

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26.1

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28.4

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64.

74.

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87.

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66.

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57

7.2

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TH

K3.

33.

23.

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65.

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D.

1.2

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1.5

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61.

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ter

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6.2

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3.9

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71.

7N

ote:

All

mea

sure

men

ts i

n m

m.

Row

-hea

ding

cod

es—

Num

ber

of s

peci

men

s; L

EN=l

engt

h; S

.D.=

stan

dard

dev

iatio

n; W

ID=w

idth

; TH

K=

thic

knes

s.

364


ter 2 are likely to be fairlyrepresentative of thelarger assemblage.

For description ofmean artifact thicknesswhere fragmentation ishigh, calculations shouldinclude thickness mea-sures of both completeflakes and proximal frag-ments. Table 2 demon-strates the general trendwhere increased frag-mentation results in anincrease in average com-plete flake thickness.When complete flakes and proximal fragments arecombined this effect is diminished (Figure 6). Al-though values fluctuate, they are less prone to over-estimation than measures of complete flakes alone.Because of this, a combination of complete flakesand proximal fragments is a better representationof mean flake thickness when fragmentation is se-vere.

CONCLUSIONThe results of this study support the follow-

ing conclusions: (1) trampling does result in con-siderable modification to chipped stone assem-blages; (2) this damage both inflates assemblagesize and deflates mean specimen size; and, (3) thereis a positive relationship between both substratecompaction and the severity of trampling damageas well as between trampling time and the degree oftrampling alteration. These factors are likely to havea significant effect on interpretations of artifactabundance, raw material proportions, and meanspecimen size unless corrective measures are taken.Minimum flake estimates (MNI and MNF) are likelyto provide a better estimation of assemblage sizeand true material proportions than do simple countsof artifacts or complete flake frequencies. Addition-ally, mean flake size can be reasonably measuredby limiting measures of length and width to com-plete flakes, and by limiting flake thickness mea-sures to complete flakes and proximal fragments.These measures, however, need qualification whenfragmentation is high.

These techniques warrant further research. In

retrospect, the flakes used for this study have littlein the way of primary reduction. This has resultedin a great deal of uniformity in terms of flake thick-ness. Additionally, the average durability of theraw materials used for this study is quite low. Hadthe experimental assemblage been composed of amore diverse range of artifacts and material types,the results of this study may have been slightlydifferent. It is unlikely that the overall utility of thesemethods would have been diminished, but greatervariety in artifact form and material durability mayhave more thoroughly demonstrated the differen-tial effects of the trampling process. Future researchon the effects of fragmentation on assemblage sizeand material proportions can further evaluate thesetechniques.

While this study has focused on the impactsof cattle trampling on the Great Plains, there are amultitude of other agents that may have similar ef-fects on surface scatters of chipped stone aroundthe world. When confronted with chipped stoneassemblages that have been exposed to fragmen-tation, no matter the agent, identification of theparticular cause of the fragmentation is not the onlygoal. In addition, deploying appropriate analyticprotocols can go a long way towards mitigatingthe effects of these alterations. The primary signifi-cance of this study is not simply greater insightinto the effects of cattle trampling, but also includesthe realization that, if dealt with appropriately, frag-mented assemblages should not to be dismissedas distorted beyond usefulness. Rather, they re-

Figure 6. Thickness (mm) error bars: (a) complete flakes; (b) complete flake and proximalfragments.

365


quire special treatment to reveal the latent informa-tion in them about past human behavior.

ACKNOWLEDGMENTSWe would like to thank the Hammons family for

allowing the completion of this work on their farm.Execution of the experiment would not have happenedwithout the help of Ben Koziol, Matthew Dooley, andMike Hammons. Simon Holdaway and Sam Lin haveprovided comments on earlier drafts of this paper. Thisresearch has been funded by a grant from the University ofNebraska Center for Great Plains Studies.

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