The Functional Morphology of the

Hominoid Foot

Francesca Campbell BSc

Registration number 120189663

UCard number 001561981

A report submitted in part fulfilment of the examination requirements for the award of an MSc

in Palaeoanthropology awarded by the University of Sheffield, 2013, supervised by Dr. Kevin

Kuykendall.

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Certificate of Originality

This is to certify that I am responsible for the work submitted in this thesis, that the original

work is my own, except as specified in the acknowledgments and in references, and that neither

the thesis nor the original work contained therein has been previously submitted to any other

institution for a degree.

Name: Francesca Campbell

Signed:

Date:

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Acknowledgements

The author wishes to thank;

Dr. Kevin Kuykendall for supervising this study.

Inbal Livne at The Powell-Cotton Museum for help and advice during data collection.

Prof. Tim Birkhead at The Alfred Denny Museum for help and advice during data collection.

Mark Edwards for advice, assistance and patience.

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Abbreviations

ABBREVIATION FULL DESCRIPTION

G. gorilla Gorilla gorilla Where G. gorilla is used, this refers to the sub species Gorilla

gorillla gorilla, the western lowland gorilla. G.g.diehli, or the

upland gorilla, is not used in this study.

H. erectus Homo erectus 1.8 - 0.2 mya

H. ergaster Homo ergaster 1.9 - 1.4 mya

H. habilis Homo habilis 2.3 - 1.4 mya

H.

heidelbergensis

Homo

heidelbergensis

0.6 - 0.35

H.

neanderthalensi

s

Homo

neanderthalensis

0.35 - 0.03 mya

H. sapiens Homo sapiens Modern humans, sometimes refered to a sub species - H. sapiens

sapiens

MT Metatarsal Metatarsal bones, numbered from medial to lateral, I - V

OH 8 Olduvai Hominid

8

H. habilis assemblage, c. 18 mya, discovered in Olduvai Gorge,

Tanzania

5

P. troglodtyes Pan troglodytes Where P. troglodytes is used, this refers to the chimpanzee species,

not to be confused with 'pygmy' chimpanzees, bonobos (P.

pygmaeus). Since this study uses research cited before the

recognition of the bonobo as a separate species, where the common

name 'chimpanzee' is used, specimens may be P. troglodtyes or P.

pygmaeus. All of the species used in this study's data collection are

P. troglodytes as specified.

PCA Principle

Component

Analysis

Data reduction technique

R R Statistics programming language developed by R Development and

Licensed by GNU General Public License

SPSS Statistical

Product and

Service Solutions

IBM SPSS statistics package

STW 573 Sterkfontein 573 The catalogue number of an Australopithecus fossil from South

Africa. Dating is difficult but most tenchniques range in the 3-4mya

bracket.

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Contents

Page

1. Abstract 7

2. Introduction 9

3. Aims and Objectives 36

4. Materials and Method 37

5. Results 47

6. Discussion 54

7. Conclusion 59

8. Further Research 60

9. References 61

10. Appendices 68

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1. Abstract

The functional morphology of the hominoid foot is reviewed with a particular emphasis on the

comparison of the species Gorilla gorilla, Pan troglodytes and Homo sapiens. Collated

measurements from specimens at the University of Sheffield and the Powell-Cotton Museum are

compared using linear divisions of the foot. Linear divisions are compared using descriptive

statistics using SPSS, average relative lengths using R, and finally analysed by PCA using SPSS.

Attention is given to the second toe due to the unique morphology of the adducted H. sapiens

hallux. From the comparative model of extant primates the foot bones of extinct homind bones

are analysed, with special attention paid to the most complete foot specimen; Homo ergaster

'Narikotome Boy', Little Foot (STW 573) and OH 8 Homo habilis. This work supports the

previous comparative work carried out by Adolph Schultz in the early 20th Century, the work

of John Napier, John Robinson in the 1960's and Will Harcourt-Smith in the late 20th and early

21st Century. The wide range of human variation is demonstrated and the results are discussed

in the context of there being a greater diversity in hominoid locomotion that the 'less upright -

more upright' model favoured for many years {fig1}. Recent developments in human walking

style are discussed in the context of a closer link between extinct species than previously

thought.

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Francesca Campbell

Figure 1. the 'less upright to more upright' model of evolution

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2. Introduction

2.1 Introduction

The evolution of mammals has created many diverse forms of locomotion, from brachiating

monkeys, swimming whales and bipedal humans. With the exception of the head, the axial

skeleton stays relatively conserved with the majority of evolutionary changes being driven by

locomotive style and behaviours, leading to diverse changes in the limbs (including the tail) and

head/brain. In the great apes, the comparative anatomy and serial homology of limbs has been

documented since Victorian times, but gained significant impact with the evolutionary studies

of Ernst Hæckel . More recent work with genetic material has led to an increased sophistication

of the homology theory; as OJ Lewis states

“homology has come to mean not merely similarity of position in a body; that is of

anatomical relationships, but also derivation by a similar pathway of development,

controlled by genealogically related genes” [Lewis, 1989, 27].

Early students of anatomy (skeletal, osteological and musculature) always considered the

similarities from a human point of view, determining the standard anatomical position in an

upright, standing pose {Fig 2}.

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Figure 2. Leonardo Da Vinci’s Vitruve Luc Viatour, c. 1490, showing standard

anatomical position; erect, with forearm supinated. Image from

wikimediacommons.com

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This view is seriously compromised by the development of the bipedal upper limb being

supinated in natural pose; in quadrupeds the upper or front limb is pronated and this is the

‘natural’ position for human limbs when assuming a position with all four limbs on the ground.

Despite the apparent differences in the function of the lower limb and foot in terrestrial

mammals due to body type and size, foot shape and function, arrangement of structures and

loading conditions, the study of comparative morphology of the foot shows many common

features of organization, structure and function.

Synthesis is clouded by the considerable variation in scale and proportions in distal limb

structure among quadrupeds, knuckle walkers and obligate bipeds. The posterior to anterior

mass loading mechanics of locomotion vary considerably due to mass and body shape, as do the

changes of distribution of mass during locomotion. Because of the wide variety of body shape,

size and mass, organization and morphology of the foot bones may vary between species.

Obligate bipedal locomotion and its temporal position in the hominid lineage is one of the most

significant events in hominid evolutionary history [Chaplin et al. 1994; Schmitt 2003; Harcourt-

Smith and Aiello, 2004]. There is considerable literature on the subject of the evolution of

hominid bipedalism, ranging from the hypothetical locomotion of last common ancestors

[Byrnes and Spence, 2011; Cartmill, 1974; Harcourt-Smith and Aiello, 2004; Jungers, 1982.,

Richmond and Strait, 2000; Richmond and Strait, 2001; Robinson and Robinson, 1972; Schmitt,

2003; Stern Jr and Susman, 1983], to ecological pressures which may have led to the positive

selection for bipedalism [Hunt, 1994; Krebs and Davies, 1978; Taylor and van Schaik, 2007] and

the degree of bipedalism exhibited by extinct hominids [Asfaw et al., 1999; Brunet et al., 2002;

Day and Wood, 1968; Gebo, 1992; Köhler and Moyà-Solà; 1997, Leakey, 1973; McHenry, 1994;

Stern Jr and Susman, 1983; White et al., 1995].

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The foot of extant primates is extremely specialised [Ali and Meier, 2008; Cartmill, 1872] ;

evidence shows that the lower limb carries the majority of the stress of locomotion even in

arboreal great apes [Schultz, 1969]. Humans, as the only extant hominid obligate biped, show a

range of unique adaptions in both anatomy and pedal function that differs from both extant apes

and extinct hominids. In obligate bipedal locomotion the lower limbs must take the forces

generated by locomotion and the entire body weight through only one foot at a time as the

movement is transferred from swing to stance phases [Lovejoy, 1988; Schmitt, 2003]. During toe

off the morphology of the foot must be robust enough to accommodate these forces and as a

result the hallux is much larger relative to the other four toes in humans than other primates

[Schultz, 1969].

2.2 Osteology of the human foot

In humans and great apes there are twenty six bones in the foot, divided into three separate

groups. The tarsals are the robust bones of the ankle, the metatarsals the smaller bones of the

instep (forming the arch of the foot in humans) and the phalanges make up the toes (seven, five

and fourteen bones consecutively). The phalanges form a homologous structure with the hand

with five proximal phalanges, four middle phalanges (the hallux having no morphologically

distinct intermediate phalanx) and five distal phalanges {fig 3}.

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Francesca Campbell

Figure 3: the bones of the human hand and foot

Due to the similarity of articulation of the bones in the hand and the foot, the joint surfaces of

these bones show some similarity. However, the foot bones can be readily distinguished from

the hand bones by the round, rather than reniform, cross sectional shape and in their general

morphology; foot phalangeal bones (with the exception of the hallux) tend to be much less

robust, smaller both absolutely and relatively, have narrower midshafts and are wider (flared) at

the proximal and distal ends [Aiello and Dean, 2006]. The human hallux is much more robust

relatively and absolutely; the first metatarsal being distinct in girth and length, due to the

unique pressures of obligate bipedality placing great bending stress and weight during the stride

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cycle, and distinct in shape; the medial head has an articular facet to allow dorsiflexion of the toe

during the toe-off phase.

The seven tarsal bones are the calcaneus, talus, navicular, three cuneiforms and the cuboid. The

calcaneus is the largest bone in the foot and forms the heel; it articulates with the talus, the

cuboid and the navicular. Identification and siding of the calcaneus and talus is not relatively

difficult since the bones are so distinctive and articulate in a regular fashion. The calcaneus has

its calcaneal tuberosity posterior and the non-articulating portion is inferior. Siding is not

difficult since the 'heel' portion is so distinctive and the position of the sustenaculum tali

indicates the side. For the talus, the saddle shaped facet is superior and the anterior point forms

the talar head. The large malleolar articulation with the fibula is on the lateral side. The talus is

the medium by which the foot is linked to the lower leg. In humans, the talus does not have a

muscle attached to it. The navicular is named for a ‘little ship’ (Latin) and bears a

correspondence to the scaphoid (‘a little boat’ in Greek) in the hand and from this the shape is

easily identified. It has a pronounced concave surface which articulates with the talus. The

convex side articulates with all three cuneiforms. The navicular tubercle is on the medial side.

The three cuneiform bones, medial, intermediate and lateral, are wedge shaped bones that form

the transverse arch of the human foot. The largest, the medial cuneiform, has a reniform facet

where it articulates with the talus. Therefore the longest surface is distal. The second largest is

the lateral cuneiform and the smallest is the intermediate. The second cuneiform (aka the

intermediate) articulates with both cuneiforms on either side. The broadest surface of the

cuneiform is dorsal and the proximal surface is the most concave as it articulates with the

navicular. The third cuneiform (lateral) is intermediate in size and articulates with MTII, III and

IV distally . The cuboid forms the top of the arch in the longitudinal arch of the human foot . The

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cuboid articulates with the navicular and the third cuneiform and is identified by the cuboid

tuberosity. The non- articular portion lies supero-laterally and the articulting facet lies on the

medial side. Shape and angle of articular surfaces of the tarso-metatarsal joint have been used to

infer bipedality [Harcourt-Smith and Aiello, 2004; Sarmiento and Marcus, 2000] and the

articular facets of the navicular have been used in a similar manner [Sarmiento and Marcus,

2000]. Round articular facets on the medial cuneiform allow a wide degree of abduction in the

primate hallux. The human medial cuneiform has a compressed articular facet which holds the

hallux into an adducted position, parallel to the other rays with extremely limited, if any, lateral

movement [Aeillo and Dean, 2006] {Figure 4}.

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Francesca Campbell

Figure 4. The bones of the human foot. Redrawn from Aiello and Dean [2006, 408]

Compared to Pan and Gorilla the human calcaneus is relatively robust and large. In humans the

calcaneal tuberosity is the first part of the body to make contact with the ground during the

stride cycle {fig 6} and as such is larger and more robust in order to provide stability. The

calcaneus serves as an attachment point for the ligaments forming the arches of the foot; these in

turn act as a spring or shock absorber [Aeillo and Dean, 2006]. The metatarsals, like the

metacarpals, are all tubular bones with the distal articular heads forming rounded stubs and the

proximal heads forming square stubs. The metatarsals are concave in lateral view and the bases

17

of MTII-V articulate with each neighbouring pair. Each of the tarsals in the distal row articulate

with at least one MT base and it is from the combination of the convex profile and the articular

facets on the base that the MT can be identified, sided and ordered. The first MT is more

massive in humans than in Gorilla or Pan but even in these two species the first MT is still

distinctive by its robusticity. Sesamoid bones present in the tendons of the muscle flexor

hallucis brevis articulate with the MTI head; in apes (especially larger species such as Pongo and

Gorilla) these sesamoid bones tend to be larger and so by extension create larger articular

facets. MTII is, in humans, the longest MT. It has a very narrow shaft in humans, Gorilla and Pan

and its two lateral facets articulate with the lateral cuneiform and MTIII. It also articulates

proximally with the intemediate cuneiform and with the medial cuneiform on the medial edge.

The base of MTII is also less platform-like than MTIII and MTIV. For this reason it may be

confused with the styloid process of MTV, especially in fragmentary assemblages; however the

articular morphology is distinctive enough for this not to be an issue for this study. MTIIIs

medial facets are similar in position to MTII but are much smaller and the base of MTIII is much

squarer due to the slight styloid projection on the MTII. MTIII also has a large tubercule on the

lateral edge. MTIV has a slightly more robust shaft than the previous two MT and it has

articulating factets for the MTIII and MTV, medially and laterally respectively. MTV is

extremely distinctive due to the protruding styloid process on the lateral side. The base of the

MTV articulates with the cuboid and forms a 'footprint' shape [White and Folkens, 2005].

As discussed previously, positioning the phalanges is difficult and so the method employed here

must be treated with a degree of consideration. The phalanges for the hallux are more

distinguishable and by comparison can be sided. The hallux lacks an intermediate phalanx and

therefore the distal phalanx is larger and more robust than the other distal phalanges. The

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remaining bones can be sorted into proximal, intermediate and distal phalanxes (3 for each ray,

12 in total) and can be sorted by comparing the associated MT head and the size compared to

other rays. Distal phalanxes II - V are almost impossible to order due to their relatively uniform

size and shape.

It has been suggested that differences in the human and ape foot are a direct result of the

remodelling of the human foot around the subtalar axis of the primitive prehensile primate foot

as a direct result of a more bipedal stance [Keith, 1929; Lewis, 1981]. It is around the subtalar

axis that the foot everts and inverts[Aeillo and Dean, 2004]. The subtalar axis differs from

humans, Pan and Gorilla in its gradient. It is steeper dorsoplanarly in humans than in apes due

to the relatively large curve of the articular surfaces in the human foot. Because of this sharp

gradient, lateral movement is severely limited in humans while apes still maintain a certain

degree of flexibility at the subtalar joint.

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Fig 5 transformation of an ape foot into a human foot, from Aeillo and Dean, 2004

(Page 518). (a) the ape MT rotate so that their head sit on the substrate (1) and the

lateral MT move medially (2) toward the subtalar axis (STA). (b) The medial

realignment of the lateral four MT (3) is associated with their angled bases (4) and

with the elongated and medially bent cuboid and lateral cuneiform (5). The talar

trochlear rotates medially on the talus (6) and the posterior portion if the

calcaneus moves laterally (7) which brings the long axis (LA) closer in line to the

STA. This results in a closer approximation between the STA and the (LA) in the

human foot (c) than the ape foot (a).

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For this reason it may be prudent to consider the functional divisions of the foot in three

segments, taking into account the lever arm portions of the foot as explained by Schultz [1963]

{fig 6}.

Fig 6 Bone and lever lengths of the human foot. After [Schultz, 1963]

The forefoot – the most distal portion of the foot, providing leverage and load transfer

properties.

The midfoot – the intermediate portion of the foot, providing force transmission through the

transverse tarsal joint from the hindfoot (subtalar joint) to the forefoot (metatarso and inter-

phalangeal joints).

The hindfoot – The most proximal part of the foot, containing the most robust structures for

transmitting force between the proximal and distal aspects of the foot during locomotion and

load bearing in standing phase. This is also the area the foot articulates with the bones of the leg,

forming the ankle joint.

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2.3 Bipedal gait

Fig 7 Walking cycle. A- distance. B - time. [from Inman et al. 1981, page 26.]

22

Phases of the gait cycle from the foot striking the ground to the same foot striking ground again.

Initial contact with substrate - extended knee, ankle in neutral anatomical position. Heel

contacts the substrate first.

Loading response - during loading knee flexes, ankle plantarflexes and gluteal muscles

remain active to maintain hip stability.

Mistance - begins with toe off. By midstance the knee is extended and the ankle is in

neutral anatomical position.

Terminal stance - Centre of gravity is maintained over supporting foot.

Pre-swing - pushes centre of gravity over supporting foot and brings opposing foot

forward to heel strike. Knee flexes and ankle plantar flexes. Toes dorsiflex at

metatarsaophalangeal joints.

Subtalar joint assumes near neutral anatomical position.

2.4 The ape gait

Walking gait differs in apes due to the morphological and musculature differences in the ape hip

and lower limb. Neither the hip joint or ankle joint are fully extended during walking and the

knee and ankle joints both stay in front of the hip during the stance phase. As a result ape stride

is shorter than human stride length and greater lateral placement is required to maintain the

centre of gravity. The swing phase is slightly different in apes too, as the musculature in the hip

does not allow for full abductor capabilities in the ape, and so the entire trunk is shifted across

the lateral plane. This style of walking requires more energy to maintain than full bipedality in

humans, and this may be why the arboreal origins theory of bipedality may have gained favour,

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since arboreal movements more closely mimic human bipedality in kinematics and energy

expenditure. This theory may be quiet attractive to those seeking an answer to why our

ancestors stood tall and our cousins did not [Aeillo and Dean, 2004].

2.5 The extant Hominoid foot

There are a number of differences between the ape and human foot, the greatest being the

opposability of the hallux in apes, a feature which is lost in humans. These differences are due to

differing style of locomotion and lower limb adaptations as a result of bipedal stance. The fully

adducted hallux reduces grasping ability in the human toes, and in general the other toes are

relatively shorter in length than in other primates. Walking bipedally with abducted hallux

restricts efficient bipedalism and so relative toe length is likely an adaptation of obligate

biedalism . In human walking, the lateral posterior aspect of the calcaneus comes into contact

with the ground (the heel). The foot then levers forward onto the lateral metatarsal (MV, or the

little toe) and the weight is then transferred medially across the foot, to the ball of the foot at the

end of MI. {fig7} The entire weight of the body is then placed on the hallux as the opposing leg

swings forward. The last part of the foot to leave the ground is the hallux during toe-off, just

preceding or in conjunction with the heel strike of the opposing foot. There is some debate,

however, about how much a difference wearing shoes makes to this arrangement in modern

human locomotion. Studies have shown that in some individuals the weight is borne on all five

metatarsal head simultaneously instead of the rolling weight transfer from lateral to medial. This

seems especially true with the common place wearing of heeled shoes (not just tall stilettos

favoured majorly by women, but even heels with a 2.5cm lift may have some effect) [Frey,

1993].Variations in the kinematics of walking and running are well documented in sports

science and athletic development but the features described above are the most common

24

trademarks of human bipedal walking and in these features the differences in the ape foot are

highlighted. For example, in P. troglodytes there is no medial transfer; the weight being

transferred from posterior to anterior in a uniform line. The lateral border of the foot comes into

contact with the ground at the same time as heel strike and the medial border follows soon after

as the foot is placed flat (or as flat as the opposable hallux will allow) on the ground. The second

and third toes are the last remaining contact with the ground, rather than the first toe in

humans. The ape footprint also exhibits a phenomenom called the ‘midtarsal break’ due to the

increased mobility of the calcaneocuboid joint in the ape foot. As the calcaneus leaves the

ground, the foot pivots at the calcaneocuboid joint and part of the lateral side of the foot comes

in contact to the ground. In humans this would be an impossibility due to the relatively high

arch of the foot and the mobility in the calcaneocuboid joint to facilitate bipedal load bearing.

2.6 The proportions of the foot

Aside from the adducted hallux in apes, a major difference between the great ape and modern

human foot is the proportion of the length of the phalanges. Humans have much shorter third

toes in relation to the other toes and the total length of the foot than great apes. In Gorilla, the

third toe represents 33% of the total length of the foot and chimpanzees it is 35% of the total

length, while in humans it is only 18% [Keith, 1929] (Schultz [1969] reports 32% for gorillas and

19% for humans.) Shorter lateral toes appears to be a response to a more terrestrial form of

locomotion, since predominantly terrestrial primates such as geladas also exhibit shorter lateral

toes relatively. The sequence of toe length also differs from humans to apes. Total toe length is

sequential in humans, from I to V. In apes, the sequence goes from III being the longest, IV, II, V

and finally I the shortest [Schultz, 1969]. Lever length in humans is also longer in relation to

trunk length than apes, despite having shorter foot length in total. Metatarsal robusticity differs

25

between humans and apes; as may be expected due to the loading forces {fig 6}; MI in humans is

very robust, followed by MV due to the large proportion of weight bearing during the lateral roll

on to the ball of the foot during walking phases. In apes, MV is the least robust due to the

majority of the weight being placed more medially towards MI during locomotion.

Figure. Representation of the average relative lengths of the functional divisions of

the foot, proportional [tarsal + MIII length = 100]. (after Schultz, 1963, reproduced

in Schultz, 1969 and Aiello and Dean, 2006)

2. 7 Fossil foot bones

Whilst early Miocene foot bones of primates have been known for a few decades, the primitive

condition in the human lineage is still under much scrutiny. Gorilla and Pan share features

26

which seem to be derived from Hylobates, such as the reniform facet for the calcaneus. Without

delving into the considerable minefield of cladistic analysis, the author has attained to the

commonly held last common ancestor theory presented in figure 7 which represents a commonly

held theory although consensus may differ on the dates involved.

Figure 7. The Hominidae family tree, based on comparative and demographic analysis of

orang-utan genome, reproduced from [Locke, Hillier et al. 2011]. See reference list for

secondary references (ref.29 and ref.30) referenced in the above image.

Australopithecine foot bones used to be limited to calcaneal and fragmentary tali and any

speculation about the bipedality of this species was based on morphology of the pelves and leg

bones. The discovery of the Laetoli footprints in 1979 by Leakey gave us the best evidence yet

that this species walked upright with a gait closer to that of modern humans than great apes,

albeit with a partially or intermediate adduction of the hallux. In addition, the talus of ‘Lucy’,

27

regardless of its fragmentary nature, seemed to suggest a relationship with the leg bones more

similar to that of the great apes [Lewis, 1989]. In 1996 a 3.2 million year old complete MIV fossil

was discovered in Hadar, Ethiopia by William Kimbel and the shape and robusticity of this bone

seemed comparable to that of modern humans; the orientation of both ends of the bone reflect

the longitudinal arch of the foot and the flat tarsal facets suggest that the midfoot was lacking a

midtarsal break which is so indicative of the morphology of the ape foot. This view was

challenged in 2012 by Yohannes Haile-Selassie when pedal elements from a 3.4 million year old

fossil also from Ethiopia seemed to suggest a species which had morphology more similar to the

primitive form of Ardipithecus ramidus, with a more abducted hallux and the possibility of

opposability in the morphology of the pedal elements, leading to the possibility that a mosaic of

different features across a number of contemporaneous species existed.

Francesca Campbell

Figure 8. The bones of the Burtele BRT-VP - 2/736 foot, drawn to a G. gorilla

footprint, from Haile-Sellaise, [2011]

28

The temporally earlier Ar. ramidus material also exhibits a mosaic of primitive and derived

features with evidence pointing to a fully abductable hallux like the primitive state, but little

lateral midfoot flexibility as shown in the more derived forms, with little evidence of a midtarsal

break.

The Homo habilis foot is best represented by an almost complete foot fossil (OH 8). The tarsals

and metatarsals have unfortunate omissions, with the metatarsal heads broken away and the

calcaneal tuber eroded, but the subsequent discovery of more material from the same site has

revealed a complete ankle joint [Lewis, 1989]. Although the reconstruction of the soft tissues of

the articulations of the OH foot have been debated, OH 8 is remarkably Pan like in proportion

and morphology.

29

Francesca Campbell

Figure 9. The bones of the OH 8 foot.

Articulation of the reconstructed OH 8 foot show the suggestion of a midtarsal break which is

characteristic of the ape foot, yet the articulations between the cuboid and calcaneus are

30

reminiscent of the ‘close-packed’ situation developed in the human foot to give stability during

load bearing [Lewis, 1989]. This evidence has led to the theory that the flexibility of the Pan and

Gorilla foot is a derived feature . Lewis [1989] and Kidd [1999] both challenge the conventional

view that the human foot is derived from a Gorilla type foot and instead propose a more vice

versa model where the ape foot is more derived from a human type foot. As Harcourt-Smith

explains

"here the first ray adducts to become in line with the functional axis of the foot, and the

foot everts so that the sole is flat on the ground" [Harcourt-Smith and Aiello, 2004, page 406-7].

Kidd concludes that the lateral side of the foot evolved into its modern state before the medial

side, based on the morphology of the OH 8 foot [Kidd, 1999]. However, he uses just one

specimen in his analyses and discounts (or ignores) some of the evidence from the tarsal bones .

The degree of variation cannot possibly be inferred from one specimen although it may help to

support other evidence. The most recent discovery of the seemingly bipedal Sahelanthropus

tchadensis from around 7mya [Brunet et al., 2002] would seem to disprove Kidd's conclusions.

2.8 The extinct hominid foot

Whilst the bipedality of species closer temporally to H. sapiens is well known [Smith and

Aiello, 2004; Aiello and Dean, 2004; Trinkaus, 1983; Lorenzo et al., 1999.] a great majority of this

work is inferred from the post cranial skeleton. For instance, AL 288-1 "Lucy", is suspected to be

bipedal from the morphology of the hip joint and no foot bones are associated with this find

[Jungers, 1988] . Later species such as H. hedelbergensis and H.neanderthalensis have differing

pedal morphology (see 2.6.) their species are clearly bipedal [Aeillo and Dean, 2004; Lorenzo et

al 1999;]. Similarly, although few foot bones are known from H. ergaster its bipedality is inferred

31

from its post-cranial morphology and cranial position. In some cases the body proportions may

be used to infer bipedality although it is imporatnt to consider that there may be a wide range of

variation in these proportions since there may also be significant differences and mosaic of

features in the early hominids due to a range of locomotive style and a mosiac of features as

result. When Day and Napier documented the OH 8 H. habilis foot {fig 9} in 1964 they argued

that the morphology of the bones reflected a fully obligate bipedal stance [Day and Napier,

1964.]. This theory was supported by Richard Leakey and Bernard Wood [Leakey et al., 1964, M.

H. Day and B. A. Wood, 1968]. The OH 8 foot seemed to Day and Napier to have a non-

opposable hallux and contained strong longitudinal arches. However, collaborative research in

the early 1990’s seemed to support the evidence that the OH 8 foot showed arboreal adaptation

[Kidd et al., 1996; Kidd and Oxnard, 2005; Bernhard Zipfel & Robert S. Kidd, 2008] In

particular, the features found show modern adapatations on the bones of the lateral side of the

foot such as the cuboid and a mosaic of features on the medial side; talus and navicular are

primitive in morphology while the cuboid shows modern features. Some researchers have used

this mosiac of morphololgic features to demonstrate an intermediate phase between the mid-

tarsal break seen in P. troglodtyes and the absence of such a feature in modern humans. This

argument has been supported by later finds such as STW 573 'Little Foot' {fig 10}, whose

hindfoot bones show a similar arrangement to the OH 8 material. STW 573 also provided

supporting evidence for the argument for an adducted hallux in OH 8, a view which was

contested until the later material was discovered. Oxnard [1972] concluded that the OH 8 tali

was significantly different from both H. sapiens and ape tali.

32

Francesca Campbell

Figure 10. The bones of the STW 573 'Little Foot', drawn to a G. gorilla footprint

STW 573 is a collection of medial foot bones consisting of a talus, navicular, medial cuneiform

and MT1 fragment. As discussed previously, the hindfoot bones present a pattern consistent

33

with the OH 8 material, and this find refutes the divergent hallux theory almost conclusively

[Zipfel and Kidd, 2006; Zipfel, DeSilva and Kidd, 2009]. Zipfel et al., [2011] describes the

findings as

“(they) collectively lead to an intregrative model of pedal evolution of caudo-cranial,

disto-proximal changes”.

However, the specimen does seem to have a hallux capable of a great degree of grasping

capability and a mobile mid-tarsal break. The species to which STW 573 is assigned is hotly

contested although it does appear to be conclusively places in the Australopithecus genus, and

conclusive evidence is clouded by the temporally contemporaneous A. afaerensis foot bones

found in Ethiopia [Walter. 1994]. The two models have been resolved into the following

conslusion; A. afarensis has a modern talus, unopposable hallux and strong longitudianal arches

but possess a primitive navicular and an ape like talocrural joint. 1

A. sediba findings [Zipfel et al, 2011] reinforce the semi-arboreal model of pedal morphology

described by Zipfel, Kidd, Oxnard and DeSilva, collectively. Morton’s [ref] 1935 hypothetical

prehuman model of the foot, which shows a divergent hallux alongside a substantial calcaneus,

would appear to be incorrect; however, the reconstruction of the STW 573 specimen by Clarke

and Tobias [1995] would appear to be in direct contrast to this view; indeed, this reconstruction

almost exactly replicates the hypothetical model proposed by Morton [Morton, 1935; Clarke and

Tobias, 1995].

Despite the comparative lack of extinct specimens to work with, Morton's work was based on a

great deal of comparative data and his conclusion is that the prehominid foot would be

somewhere intermediate between that of Gorilla and H. sapiens due to the terrestrial nature of

34

Gorilla, as opposed to the more arboreal Pan. There are features of the Gorilla foot that may

support this argument; a more robust heel (as seen in the OH 8 specimen), MTII to MTV

relatively smaller in size and a less abducted hallux and no longitudinal arch present. Indeed,

many reconstructions of hominid fossils are drawn to a Gorilla footprint/outline. Morton also

outlined how the prehuman foot would have differed from the Gorilla morphology - a relatively

long opposable hallux, an even larger heel and shorter toes than the Gorilla. Harcourt-Smith

[2004] notes the similarity between Morton's reconstruction and Clarke and Tobias' 1995

reconstruction of the STW 573 foot. Morton's work underwent something of a revisionst phase

in the 1990's when the theory that Gorilla and Pan feet were distinctly modified to cope with

increased body weight, especially in the case of male Gorilla which may be up to 60% larger than

the female.

2.9 H. neanderthalensis foot morphology

The most complete pedal elements of H. neanderthalensis are La Ferrassie 1 and the morphology

of the feet and the rest of the post-cranial skeleton are fully adapted to bipedal locomotion

[Trinkaus, 1983]. H. neanderthalensis feel are similar to H. sapiens in the gross morphology, yet

the H. neanderthalensis show a greater degree of robusticity and the musculature attachment

sites are much more strongly developed. [Aeillo and Dean, 2004]. H. neanderthalensis also sho a

unique pattern in that the proximal phalanges are wider than they are high while the opposite is

true for H. sapiens. The proximal phalanx is relatively short compared to total foot length, and is

reflected in the serial homology of the hand. The hallux shows a small degree of adduction but

does not appear to be opposable [Trinkaus, 1983]. In other areas, the H. neanderthalensis foot is

35

indistinguishable from H. sapiens. Highly characteristic, however, is the talus neck in H.

neanderthalensis , which is relatively short, although this appears to be a secondary adaptation

to a high muscle mass and does not appear to have much functional significance. [Aeillo and

Dean. 2004].

36

3. Aims and Objectives

It is the aim of this research to analyse the linear dimensions of the foot of modern humans and

great apes (Gorilla gorilla and Pan troglodytes), and compare those analyses to published data

on fossil hominids. The research attempts to synthesise comparative data by analysing

measurements on non-articulated remains to reflect the nature of the fossil record. Increased

knowledge on the subject of structure of the hominid foot and its relationship to locomotor style

is important in our understanding of human evolution and bipedality.

37

4. Materials and Methods

4.1 Introduction

In humans, the bones of the foot are serial homologies of the bones in the hand and are usually

described in a similar way to the hand bones - tarsal bones (calcaneus, talus, lateral cuneiform,

medial cuneiform and intermediate cuneiform, navicular and the cuboid), the metatarsals

(numbered I to V from medial to lateral) and the phalanges (two for ray I and three each for rays

II to V). Occasionally sesamoid bones may be present and are more common in primates

[Nystrom, 2011]. In common terms the foot is divided into four sections; the heel, the ankle, the

arch of the foot and the toes.

The heel is defined as the prominence at the end of the foot, the most posterior aspect of the

foot. The bony aspect of the calcaneus, the calcaneal tuberosity, forms the posterior projection of

the heel and lies posterior to the articulation of the talocrural region of the ankle.

The ankle is defined as the talocrural region and forms the articulation between the bones of the

foot and the distal end of the tibia and fibula. The ankle is formed of three articulated hinge

joints; the talocrural joint, the subtalar joint and the inferior tibialfibular joint. These joints are

primarily associated with plantarflexion and dorsiflexion of the foot in humans since the

'locked' ankle configuration allows for only a little movement mediolaterally (inversion and

eversion) and in circumvention. Thus the ankle joint is involved in lower limb stability.

Dorsiflexion is the movement of the dorsum of the foot towards the anterior surface of the leg.

This movement is essential in order to have the heel strike the ground first during heel strike

and to clear the foot from the ground during the swing phase of walking. Plantar flexion occurs

38

when the toes are in contact with the substrate and the heel is raised. This movement provides

propulsion and force to lift the limb off the substrate and start it swinging forward during toe-

off phase of walking.

The longitudinal arch of the foot can be broken down into several smaller arches; the medial

arch, the lateral arch and the fundamental arch. The medial arch is formed higher on the foot,

more dorsally, and is mostly responsible for the 'missing' part of the medial side of the foot in a

typical human footprint. The medial arch is made up of the calcaneus, talus, navicular, the

medial, intermediate and lateral cuneiforms and MTI-III. The most dorsal aspect of the

longitudinal arch is at the articular surface of the talus. The bony arch is maintained by strong

plantar calcaneonavicular ligament ('spring' ligament and the tibialis posterior tendon

supporting the arch inferiorly as well as the plantar aponeurosis and the intrinsic and extrinsic

muscles and tendons of the sole of the foot. The major function of the arch is elasticity and to act

as a shock absorber when bearing the entire weight of the bipedal skeleton, especially whilst

running or jumping where a great deal of pressure is placed on the relatively small foot bones.

39

Francesca Campbell

Figure 11. Representation of the direction of the medial and lateral arches of the

foot.

40

The lateral arch also consists of the calcaneus, the cuboid and MT IV and V. It is elevated

dorsally although is not as high as the medial arch. The major function of this arch is strength,

especially in dorsiflexion and plantarflexion of the foot and as such is supported by the tendons

of the extensor muscles as well as the long plantar and the intrinsic muscles such as flexor

digitorum brevis.

The fundamental longitudinal arch is made up from aspects from both the medial and lateral

longitudinal arches and consists of the calcaneus, cuboid, lateral cuneiform and MTIII. This is

described as the fundamental arch since the removal of all the other bones in the foot would

nevertheless leave this arch in place, due in part to the shape and articulations of the bony

structures if the arch.

It is convenient to categorise the bony divisions of the foot (hindfoot, midfoot, and forefoot) but

it is necessary for this research to define the functional divisions of the foot. Whilst the ankle

and heel may be clearly defined as the talus and calcaneus, the author has chosen to include

within this functional division the cuboid and navicular due to the way the bones articulate and

the biomechanics of walking {Fig 7}. It is most important to take into account the plantigrade

walking style of Pan and Gorilla and may reflect primitive condition and walking style of

hominids that may not have had a fully formed longitudinal arch. For this reason, the G. gorilla

dimensions are used as a hypothetical 'primitive' model.

41

42

Francesca Campbell

Figure 12 A, B, C - breakdown of the divisions of the foot and where linear

measurements were made. Displayed on a G. gorilla foot for clarity regarding

measurement of the divergent hallux.

The foot was divided into three sections, labelled A, B and C.

Section A is defined as the hind division of the foot (Hindfoot). It is measured via the following

method.

A = {Aa + Ab}

where Aa = maximum calcaneal length

Ab = length of navicular measured at a 15% from the centre of the 'boat' shape [fig 12 A,

13]

Section B is defined as the mid division of the foot (Midfoot). It is measured via the following

method.

B = {Ba + Bb}

where Ba = maximum length of intermediate cuneiform

Bb = maximum length of MTII

43

Section C is defined as the foremost division of the foot (Forefoot). It is measured via the

following method.

C = {Ca + Cb + Cc}

where Ca = maximum length of proximal phalanx II

Cb = maximum length of middle phalange. Due to the inconsistencies of distinguishing

middle phalanges, the second longest phalanges were chosen for G. gorilla and P. troglodytes

and the third largest for H. sapiens, based on Schultz average relative lengths.

Cc = maximum length of distal phalange. As before, due to the inconsistencies of

distinguishing distal phalanges, the an average of the distal phalanges was taken for G. gorilla

and P. troglodytes and for H. sapiens.

44

Campbell

Figure A, B, C - breakdown of the divisions of the foot across species.

The foot bones were, if not stored as such, sorted into left and right. Although left measurements

were taken, only data from the right side are used for analysis. The tarsals were separated and

checked that siding was consistent with the curation. The MT were sorted according to

morphological features and sizes as described in the introduction. Phalanges were separated and

proximal phalanges ordered according to articulations with the associated MT and the

morphology. The intermediate phalanges were sorted according to size (H. sapiens III, II, IV, V;

P. troglodytes II, III, IV, V; G. gorilla V, III, II, IV) - however due to the fairly uniform nature of

the distal phalanges, all measurements were taken and an average calculated.

45

A pilot study for this project was undertaken in May 2013 to iron out any discrepancies with

using disarticulated remains, to develop a uniform method of collecting data, and to enhance a

method of measurement that was consistent across species. During the pilot study for this

project, five genera of primates were used to collect data; Pongo, Hylobates, Gorilla, Pan and

Homo. These species were chosen to give a cross section of size, sexual dimporhism and

locomotive style. However, when taking the number of measurements required into account,

along with the desire to gain a representative sample (n=30), it was subsequently it was decided

by the author to focus on three major species; Gorilla, Pan and Homo, and compare these species

to extinct hominids. Some data from the pilot study is used during analysis for comparison.

A sample of modern human specimens and modern primate specimens was measured to the

nearest 0.1mm using digital calipers. Individual bones and functional divisions of the foot were

measured and the combined distances compared. Dimensions compared were length of

individual bones and length of functional divisions of the foot {Fig12, 13}.

Material was from the skeletal collections housed at; The University of Sheffield; The University

of Lincoln; The Alfred Denny Museum, Sheffield; The Western Bank Museum, Sheffield; and the

Powell-Cotton Museum, Quex Park, Kent. In addition, cast material from The University of

Sheffield and published data were used for extinct hominid data collection. Measurements from

both feet were taken where possible, but for consistency comparative data was used from the

right foot where possible. Figure 12 summarises the measurements taken and indices will be

calculated from these measurements. Body size was not taken into account although records

exist. Body size may also be estimated using published formulae. Data collection pro-forma may

be found at Appendix A.

46

4.2 Materials

Digital calipers were Wilko make, model D406/07 (resolution 0.001mm, accuracy 0.02mm) and

were thoroughly cleaned and calibrated prior to use using a micrometer and gauge blocks, with

kind permission of the laboratory staff at The University of Lincoln. Both inside and outside

jaws were calibrated although only outside jaws were used to take measurements.

Measurements taken at the Powell-Cotton Museum were all disarticulated specimens. Infant,

juvenile, ‘young adult’ and ‘old adult’ specimens were discounted, only those categorised as

‘adult’ were used.

4.3 Hominid measurments

Where possible, measurements were taken from published data for pedal elements in the fossil

record. Some measurements were taken from cast collection at The University of Sheffield

where disarticulated remains were used where possible to keep with the experimental design.

47

5. Results

Data from 30 specimens (for each species) were collected. Data was shown to be normal as

displayed in the table {1}

G. gorilla P. troglodytes H. sapiens

A -

Hindfoot

0.08 0.07 0.94

B - Midfoot 0.20 0.2 0.13

C -

Forefoot

0.20 0.08 0.06

Table 1 Kolmogorov-Smirnov test significance test results N = 30

48

Figure 13 functional division as a % of total (=100) foot length.

49

Fig 14 Relative ratio dimensions reduced to G. gorilla length (=100)

based on Morton's hypothesis that Gorilla may closest represent the

state of the pre-human foot.

0

20

40

60

80

100

120

140

160

G. gorilla P. troglodytes H. sapiens

Rea

ltiv

e ra

tio

%

Species

A

B

C

50

51

Table 2 One way ANOVA results (N=30)

52

Table3 Results for Post-Hoc Tukey test (N=30)

There was a statistically significant difference between groups as determined by one way

ANOVA (A = F (2, 87) 160. p=<0.001) (B = F (2, 27) 196. p=<0.001) (C = F = (2,87) 59. p=<0.001). A

Post Hoc Tukey test revealed the Ankle (A) was significantly different between all three species

(p= <0.001), the midfoot (B) was significantly different between all three species (p=<0.05), and

that the forefoot (c) was significantly different between human-chimp and human - gorilla

(p=<0.001). There was no significant difference in the forefoot (C) between chimp and gorilla (p =

0.06).

53

Fig 16 Box and whisker plots for the Hindfoot (A), Midfoot (B) and the Forefoot (C) for G.

gorilla, P. troglodytes and H. sapiens. (N=30. measurement in mm)

BRT-VP-2/736

OH8

MT 2

STW 573

54

6. Discussion

Data from 30 specimens for each species was taken {table 1}. Although this data was shown to be

normal using the Kolmogorov-Smirnov significance test, ideally a larger data set would be

collected and collated and this would have the effect of creating a better data set for PCA to be

more effective.

As expected, the {fig 14} bar charts show that G. gorilla have functional divisions at fairly

uniform lengths. P. troglodytes show relatively larger toe length which may be a response to a

more arboreal lifestyle than Gorilla. H. sapiens show a relatively large hindfoot length due to the

kinematics of heel strike in bipedal walking. Interestingly, the Burtele foot bones show a ratio

more closely aligned with the Pan arrangement than in Gorilla which may reflect the arboreal

nature of this species.

{Fig 14} shows a similar situation when displayed as a % of the Gorilla foot, where Gorilla is

100%. Pan show relative dimensions at between 90% and 140% of the Gorilla measurements

reflecting the longer toes in Gorilla and Pan. In H. sapiens functional divisions are consistently

smaller than in Gorilla, which may be a reflection of the morphological changes in Gorilla due to

increased body weight.

55

Fig 16 shows box and whisker plots for the median, interquartile range and outliers for the three

species studied. These box and whisker charts show the massive range of human variation

compared to the relatively small variation demonstrated by G. gorilla, even when considering

the sexual dimorphism of Gorilla it is very noticeably exactly how much variation there is in a

such a small human sample. The range of human variation is not something that is very well

documented in literature and a massive study would be required to assess this fully, but a larger

data set than 30 specimens would help to clarify this study in a greater context. Specimens from

a more international range to help assess the range of geographical and regional variation may

also shed some light on exactly how much the range of human variation differs. In fact, at the

time of writing, a pre-released paper by Jeremy DeSilva [June 2013] seems to show that around 1

-1 3 modern humans show evidence of a midtarsal break, research which has gone against many

previous comparative studies. In fact, the phenomenon has been document by podiatrists who

did not realise the link between this feature in feet and our evolutionary history. DeSilva plans to

assess this intriguing data further by undertaking an ambitious project involving MRI scans and

3D printing techniques to visualise the walking mechanism of these so called 'floppy feet'. Most

previous studies have shown human feet to be much more rigid with the bones in a 'close

packed' position, with the bones connecting to form the arch and the spring mechanism of the

foot. The connection to the A. sediba fossils cannot be underestimated and these findings may

suggest and even closer link from us to the A. sediba material than anyone previously dare guess.

56

Fig 17 pressure footprints taken by DeSilva at the Boston Museum [DeSilva, 2013]

The hyperpronation of the foot creates a midtarsal break, disrupting the usual 'heel strike'

pattern of walking. It is also noted that these people tended to have larger MBI than people who

created more 'normal' walking cycle. This research once again raises the question of what it is to

be human and where the boundaries between our species lie. It also poses questions beyond the

realm of morphological similarities about the recent Out Of Africa total-replacment model of

evolution in the human lineage since it may suggest that more archaic interbreeding may have

been taking place than we can have predicted.

57

Table 3 shows the results of the one way ANOVA, showing that despite quite a large range of

overlap between the species there is none the less a significant difference between the three

species in all three divisions of the foot; however the post-hoc Tukey shows that there was no

significant difference between the chimp and gorilla forefoot; P. trogloytes having a wider range

of variation than Gorilla in this division.

Fig 17 plots selected hominid specimens against the three species surveyed. All of these data are

outside the range for human variation, especially in the hindfoot region, as may be expected due

to the highly developed human foot. However, the hindfoot measurements are also well out of

the range for Gorilla range, refuting the theory that Gorilla may be more similar to the primitive

style. However, these species also vary from each other; since we cannot know the range of

variation exhibited in these species from a handful of fossils, it is impossible to say which of

these differences are significant; however it may be reflective of the range of locomotive styles

and a mosiac of morphological features across contemporaneous species. The midfoot in humans

is highly developed which may account for the wide difference between humans and fossil

homindis. Again, the situation between extinct hominids and Gorilla is repeated, with Gorilla

showing relatively large midfoot measurements but with a narrow range of variation. It is

important to consider that OH 8 is a juvenile specimen and may not represent the fully

developed ratio of linear measurements. Forefoot measurements are difficult to assess in fossil

hominids as the distal phalanges are often lost, and the Burtele foot displays out of the charted

range, well below all three species surveyed.

Since only phalanges are available for A. afarensis, it is difficult to chart this species against the

parameters of this study. However morphology of these bones reflects a mosaic of features. The

58

general sizes and relative dimensions are more ape-like than human which highlights the

importance of supporting the study here with morphological features also present.

59

7. Conclusion

This study supports the conclusions of the work of other researchers that both primates and

humans have separately evolved a unique mosaic of features derived from an unknown collection

of primitive features. Since the primitive condition is as yet unknown, and the hypothetical

model which has been prevalent for the past century has been disproved, it is suggested that

further work must be done to fully understand the wide range of locomotive styles present in

the hominid family tree. Tarsal bones of African Miocene apes show specializations

characteristic of hominoid evolution and provide reasonable precursors for the morphology of

Pan and Gorilla. The OH 8 foot shows many ape-like features, with many close

resemblances to Pan. The relative lengths support this conclusion, and although fairly clearly

from a bipedal primate, it lacked important functional specializations found in the human foot.

60

8. Further Research

This research may be continued to its maximum efficiency via the following methods

Widening the number of specimens and the range of data collected

Extending the study to include a wider range of locomotive styles, including more

terrestrial and habitual bipeds such as Hylobates and Gelada.

Assess the range of human variation across time and geographical location

DeSilva's work on the mid-tarsal break in humans may also inform many aspects of this

study further

Develop better understanding of the long term effect of shoe wearing in the modern

human lineage.

61

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10 - Appendices Appendix A - proforma for data collection

69

Record

Specimen

Species

Condition

Sex

Side

1 2 3 ave

Calcaneal length 89.02 89.66 89.55 89.41

height (max)

width (max)

Cuboid length - 26.68 26.54 26.61

Cuboid width - 24.91 24.56 26.61

Cuneiform I length

Cuneiform I width

Cuneiform II length

Cuneiform II width

Cuneiform III length

Cuneiform III width

Navicular width20.88 18.78 27.10 -

Navicular length

MT I length 67.11 66.25 66.50 66.62

width (max)

height (max)

MT II length 84.45 83.11 83.78

width (max)

height (max)

MT III length 83.57 83.48 83.37 83.47

width (max)

height (max)

MT IV length 86.02 86.19 83.49 85.23

width (max)

height (max)

MT V length 87.50 87.40 86.30 87.07

width (max)

height (max)

Prox phalanx I - 32.55 32.55 32.55

width (max)

height (max)

Prox phalanx II - 48.90 45.60 47.25

width (max)

height (max)

Prox phalanx III - 49.25 46.25 47.75

width (max)

height (max)

Prox phalanx IV - 16.34 14.41 15.38

width (max)

height (max)

Prox phalanx V - 38.81 36.53 37.67

width (max)

height (max)

M Phalanx II - 23.36 22.46 22.91

width (max)

height (max)

M Phalanx III - 30.41 29.45 29.93

width (max)

height (max)

M Phalanx IV - 28.49 27.45 27.97

width (max)

height (max)

M Phalanx V - 21.68 21.45 21.57

width (max)

height (max)

Dist phalanx I - 21.31 21.55 21.43

width (max)

height (max)

Dist phalanx II - 16.90 16.24 16.57

width (max)

height (max)

Dist phalanx III - 18.10 18.50 18.30

width (max)

height (max)

Dist phalanx IV - 16.64 16.45 16.55

width (max)

height (max)

Dist phalanx V - 13.91 13.56 13.74

width (max)

height (max)

P/C Merfield

MIII 28

Gorilla gorilla

complete adult

male

right

36.22

25.21

53.48

24.87

25.05

21.80

54.68

60.78

23.24

17.56

27.66

21.33

18.64

23.28

17.74

17.40

15.94

16.99

13.76

20.24

13.13

30.72

22.86

25.19

10.74

16.45

11.44

13.49

11.39

12.07

14.73

16.44

15.31

14.56

12.88

13.54

8.23

11.04

8.59

8.90

6.83

9.09

17.55

9.18

11.97

9.30

11.76