Finite Element Analysis of ursid cranial mechanics and the prediction of feeding behaviour in the extinct giant Agriotherium africanum: the bare facts

Abstract

Historically, predicting ursid feeding behaviour on the basis of morphometric and mechanical analyses has proven difficult. Here, we apply three‐dimensional finite element analysis to models representing five extant and one fossil species of bear. The ability to generate high bite forces, and for the skull to sustain them, is present in both the giant panda and the gigantic extinct Agriotherium africanum. Bite forces for A. africanum are the highest predicted for any mammalian carnivore. Our findings do not resolve whether A. africanum was more likely a predator on, or scavenger of, large terrestrial vertebrates, but show that its skull was well‐adapted to resist the forces generated in either activity. The possibility that A. africanum was adapted to process tough vegetation is discounted. Results suggest that the polar bear is less well‐adapted to dispatch large prey than all but one of the five other species considered.

Full text

Finite element analysis of ursid cranial mechanics and the
prediction of feeding behaviour in the extinct giant
Agriotherium africanum
C. C. Oldfield1, C. R. McHenry2, P. D. Clausen1, U. Chamoli3, W. C. H. Parr3, D. D. Stynder4&S.Wroe
3
1 Mechanical Engineering, School of Engineering, The University of Newcastle, Newcastle, NSW, Australia
2 Department of Anatomy and Developmental Biology, School of Biomedical Sciences, Monash University, Clayton, Vic., Australia
3 School of Biological, Environmental and Earth Sciences, University of New South Wales, Sydney, NSW, Australia
4 Department of Archaeology, Faculty of Science, University of Cape Town, Rondebosch, South Africa
Keywords
Agriotherium africanum; ursidae; feeding
behaviour; finite element analysis; bite
force.
Correspondence
Stephen Wroe, Computational
Biomechanics Research Group, School of
Biological, Earth and Environmental
Sciences, University of New South Wales,
Kensington, NSW 2052, Australia. Tel: +61 2
9385 3866; Fax: +61 2 9385 2202.
Email: s.wroe@unsw.edu.au
Editor: Andrew Kitchener
Received 30 May 2011; revised 7 August
2011; accepted 30 August 2011
doi:10.1111/j.1469-7998.2011.00862.x
Abstract
Historically, predicting ursid feeding behaviour on the basis of morphometric and
mechanical analyses has proven difficult. Here, we apply three-dimensional finite
element analysis to models representing five extant and one fossil species of bear.
The ability to generate high bite forces, and for the skull to sustain them, is present
in both the giant panda and the gigantic extinct Agriotherium africanum. Bite
forces for A. africanum are the highest predicted for any mammalian carnivore.
Our findings do not resolve whether A. africanum was more likely a predator on,
or scavenger of, large terrestrial vertebrates, but show that its skull was well-
adapted to resist the forces generated in either activity. The possibility that A. af-
ricanum was adapted to process tough vegetation is discounted. Results suggest
that the polar bear is less well-adapted to dispatch large prey than all but one of
the five other species considered.
Introduction
The identification of relationships between form and function
in mammalian carnivores has been the subject of numerous
morphometric and biomechanical studies (Radinsky, 1981a,b;
Van Valkenburgh, 1985; Werdelin, 1986; Thomason, 1991;
Therrien, 2005; McHenry et al., 2007; Wroe et al., 2007; Wroe
& Milne, 2007; Wroe, 2008; Wroe, Lowry & Anton, 2008;
Slater & van Valkenburgh, 2009; Goswami, Milne & Wroe,
2010). The results of such analyses have been useful to both
evolutionary biologists and palaeontologists seeking to
predict behaviour in fossil species. Correlations have been
established between skull shape, mechanical behaviour and
diet in many mammalian carnivore taxa. However, among
these, extant bears (Ursidae) have been perhaps the most
intractable (Radinsky, 1981b; Slater et al., 2010).
Some relationships remain uncertain among bears, but
Ursidae is clearly a relatively young family that diverged from
dog or dog-like caniform ancestors around 23–24 million
years ago [McLellan & Reiner, 1994; Krause et al., 2008; and
see Supplementary Information (SI) Fig S1]. Despite this
recent origin, living ursids span a very wide range of feeding
ecologies, from specialized herbivory to hypercarnivory,
making the failure to find strong correlations between
common mechanical or morphometric indicators and diet in
bears surprising (Radinsky, 1981b; Sacco & Van Valken-
burgh, 2004). For example, among carnivorans in general, a
relatively short skull is often associated with active predation
and carnivory, yet these are particularly well-developed fea-
tures in the most herbivorous of bears, the giant panda, Ail-
uropoda melanoleuca. Similarly, bite force adjusted for body
mass, which correlates with relative prey size for many extant
carnivorans (Wroe, McHenry & Thomason, 2005), is also
highest among this specialized herbivore. At the other end of
the extant ursid feeding spectrum, results from a recent finite
element analysis (FEA) suggest that the cranium of the most
carnivorous living ursid, the polar bear, Ursinus maritimus,
shows no special adaptations to a meat-eating habitus relative
to its more herbivorous close relative, the brown bear, Ursus
arctos (Slater et al., 2010).
As noted previously (Wroe et al., 2005; McHenry et al.,
2007; Wroe et al., 2008), if other aspects of anatomy for a
Journal of Zoology
Journal of Zoology. Print ISSN 0952-8369
Journal of Zoology 286 (2012) 163–170 © 2011 The Authors. Journal of Zoology © 2011 The Zoological Society of London 163

species under consideration differ markedly from those of
related taxa, then bite force alone may prove a poor predictor.
High bite forces in the giant panda likely represent a unique
adaptation to specialized bamboo feeding. Tooth, mandibular
and masticatory muscle anatomy in this species have all been
considered both highly specialized within the family and con-
sistent with increased herbivory on tough plant material
(Davis, 1964; Endo et al., 2003).
In recent years, some progress has been achieved in the
identification of craniodental features related to herbivory in
living ursids using a morphometric approach (Sacco and
Van Valkenburgh, 2004; Christiansen, 2008; Figueirido
et al., 2010). Two-dimensional (2D) analyses of bite mechan-
ics and mandibular force profiles have also identified fea-
tures considered consistent with specialized herbivory in
the giant panda (Christiansen, 2007). It has been concluded
that the giant panda was the only specialized extant
ursid in terms of craniodental morphology and bite force
(Christiansen, 2007).
Regarding fossil ursids, the feeding ecology of short-faced
bears, which include the largest known species, remains par-
ticularly contentious. Although arguments based on both
morphology and isotopic data have been mounted for
increased reliance on large vertebrates as food (hunted and/or
scavenged) in a number of short-faced bear species (Hendey,
1980; Mattson, 1998; Sorkin, 2006; Soibelzon & Schubert,
2011), there remains little clear evidence from analyses of skull
mechanics identifying specializations for carnivory.
In the present study, we address ursid cranial mechanics by
applying three-dimensional (3D) FEA to six skulls represent-
ing five extant species. FEA is a promising approach in bio-
logical form–function studies, but its application has been
somewhat limited by small datasets, which have typically
included two or three species (McHenry et al., 2007; Wroe
et al., 2007; Bourke et al., 2008; Wroe, 2008; Wroe et al., 2008;
Slater & van Valkenburgh, 2009; Chamoli & Wroe, 2011).
The extant species modelled are as follows, including esti-
mates of the percentage of vertebrate food comprising the
diets of each [see Figueirido et al. (2010) and Mattson (1998)]:
A. melanoleuca (giant panda) (0%); U. arctos (brown bear)
(36%), Ursus americanus (black bear) (2%), Ursus maritimus
(polar bear) (100%) and Ursus thibetanus (Asian bear) (2%).
In addition to finite element models (FEMs) of these extant
taxa, we further reconstruct the skull of the fossil Agrioth-
erium africanum (tribe Ursavini). Traditionally, it has been
argued that the extinct giant short-faced bears, Agriotherium
and Arctodus (tribe Tremarctini), were hypercarnivorous and
more active predators on large terrestrial prey than any living
bear, largely on the basis of craniodental morphology
(Hendey, 1980). This is because both genera exhibit a range of
independently evolved traits, including a short, broad skull,
premasseteric fossa on the mandible and well-developed car-
nassial blades (Kurtén, 1967; Hendey, 1980; Sorkin, 2006).
The relative importance of vertical shearing in the dentition is
widely considered an important indicator of carnivory (Van
Valkenburgh, 1989; Wroe, Brammal & Cooke, 1998) and a
predaceous, felid-like feeding ecology for A. africanum has
been hypothesized (Hendey, 1980).
More recently, however, it has been argued that Agrioth-
erium and Arctodus were probably neither active predators
of large prey nor hypercarnivores, although both likely
consumed larger quantities of vertebrate prey than most
living ursids in the form of carrion (Sorkin, 2006). A niche as
scavengers of large vertebrate carcasses and predators of
small prey supplemented with plant material has been pro-
posed (Sorkin, 2006). Sorkin drew analogy with the living
brown and striped hyaenas (Parahyaena brunnea and Hyaena
hyaena) as opposed to large felids. The argument was based
on a range of observations, including the high degree of
wear on the carnassial teeth of a North American specimen
of Agriotherium. Wear is far less pronounced in the specimen
of A. africanum included in our analysis (Fig. 1), and it
may be that proportions of killed to scavenged vertebrates
varied considerably within the genus, or that our specimen
is a younger individual. While recent studies by Figueirido
& Palmqvist (2009) and Figueirido et al. (2010) support
Sorkin’s (2006) conclusion that Arctodus was more of
an omnivore than a hypercarnivorous active predator,
no further work in this regard had been carried out on
Agriotherium.
Based on analyses of our FEMs, we ask a range of ques-
tions and test a number of predictions, some of which would
not be possible with smaller datasets.
Where dental or craniomandibular morphology are con-
sistent with increased herbivory in ursids, then a capacity to
generate relatively high bite forces may indicate reliance on
particularly tough foods as opposed to predation on relatively
large prey.
(1) Is the skull of a near obligate herbivore such as the giant
panda relatively better adapted to resist high reaction forces
generated at the molars, where bamboo is primarily processed?
Figure 1 (a) Lower left carnassial blade of Agriotherium africanum
SAM-PQL 45062 generated using computed tomography (CT) data. (b)
Lower left carnassial blade of Canis lupus (grey wolf), C. lupus (TMM
M-1709) CT.
Cranial mechanics of bears C. C. Oldfield et al.
164 Journal of Zoology 286 (2012) 163–170 © 2011 The Authors. Journal of Zoology © 2011 The Zoological Society of London

With respect to diet and ecology in the extinct A. africanum,
we address the following:
(2) Regardless of whether A. africanum was a more regular
predator of large prey or whether it consumed a high proportion
of large vertebrate bones relative to extant species, if either
interpretation is correct, then we would predict that this species
was capable of generating relatively high bite forces and that its
skull was well-adapted to sustain such forces.
In comparative FEA, single specimens are routinely used to
represent entire species. An assumption here is that interspe-
cific differences outweigh intraspecific ones. Our analyses
include FEMs of two polar bears.
(3) We ask whether the mechanical behaviours of these two
conspecifics are more similar to each other than to other species.
Although our sample is tiny, it will nonetheless allow a limited
first test of this assumption.
Materials and methods
Seven finite element models were assembled from computed
tomography (CT) data representing five extant species (brown
bear, Asian bear, black bear, polar bear and giant panda) and
one fossil ursid A. africanum (SI Table S1). For extant taxa,
preprocessing followed the previously published protocols
(McHenry et al., 2007; Wroe et al., 2007; Moreno et al., 2008;
Wroe, 2008; Degrange et al., 2010; Wroe et al., 2010).
The fossil skull (SAM-PQ 45062) that formed the basis of
our A. africanum FEM (and see SI) is without obvious defor-
mation but missing data comprise the majority of the left
parietal, frontal bones and the palate. Virtual reconstruction
to replace these missing data develops previously published
protocols (Wroe et al., 2010). Preprocessing of the extant bear
material also largely follows the published methodology
(McHenry et al., 2007), but with the surface and solid meshes
generated in Harpoon® (version 3.6, Sharc Pty Ltd., Man-
chester, UK). Each cranium comprised ~1.5 million elements.
To reconstruct A. africanum, we first used Rhinoceros®
(version 4, McNeal & Associates, Seattle, WA, USA) to
mirror the right parietal and frontal bones. Then, a polar
bear source mesh was warped to fit A. africanum in Land-
mark® (version 3.0, Institute for Data Analysis and Visuali-
zation, Davis, CA, USA). Six point primitives and 150
curved primitives were placed in Landmark on the interior
and exterior surfaces of the source and target (A. africanum)
meshes, allowing the polar bear cranium mesh to be warped
to the same shape of A. africanum. A solid mesh was gener-
ated in Harpoon® from this complete surface mesh. For all
subsequent analyses, FEA was performed using Strand7
(version 2.4.4, Company: Srand7 Pty Ltd., Sydney, Aus-
tralia). To allow comparison between the extant species and
the reconstructed fossil, models used a homogeneous, iso-
tropic material property set, with solid elements representing
bone assigned a Young’s modulus of 13 000 MPa and a
Poisson’s ratio of 0.4.
Loadings comprised two intrinsic (bilateral biting at the
canines and unilateral biting at the second molars) and two
extrinsic load cases. These simulations were designed to
approximate behaviours associated with killing and feeding
(McHenry et al., 2007; Wroe, 2008). To examine the degree to
which strain distributions and magnitudes varied between
species-specific loadings, muscle forces for these intrinsic loads
were determined on the basis of estimated cross-sectional
areas (Thomason, 1991; Wroe et al., 2005) (see SI Table S2).
Bite forces and bite force quotients [i.e. bite forces adjusted
for body mass (Wroe et al., 2005)] were derived from the
unscaled FEMs (see Table 1). Body masses were estimated for
each specimen using an equation presented for ursids based on
skull length (Van Valkenburgh, 1990).
To compare mechanical performance between specimens,
we scaled all FEMs to a uniform surface area (Dumont,
Grosse & Slater, 2009). For intrinsic loads, we adjusted muscle
recruitment to achieve a uniform bite force (Wroe et al., 2010).
Two uniform extrinsic loads were also applied to the scaled
models (lateral shake and pull back).
Statistical treatments largely concentrated on mandibular
data because inspection of visual plots clearly showed higher
and more variable strains in the mandibles. However, a two-
way analysis of variance (ANOVA) also incorporated regions
of the crania, which experienced high strain. Using code
written in R (version 2.12.1) by H. Richards, for each simula-
tion, mean von Mises (VM) ‘brick’ strain data were compiled
(Table S3).
Two-factor without replication ANOVA at 1% level of sig-
nificance (a=0.01) was performed on the mean brick VM
strain data for five different regions of the skull (left zygo-
matic arch, right zygomatic arch, rostrum, left dentary and
right dentary) for the seven specimens included for the bilat-
eral canine biting case. Once selected, regions were preset as
groups containing a constant number of elements in Strand7
(version 2.4). The rostrum was defined as that part of the
cranium anterior to the rim of the orbit, and the zygomatic
arch was defined as that part of the jugal posterior to the
anterior rim of the orbit and squamosal anterior to the
glenoid fossa. P-values were used to test the null hypothesis
that there was no statistically significant variation in the
mean VM brick strain distribution across and within the
species, and that any observed difference was because of
the sampling error.
Pairwise two-factor without replication ANOVA at 10%
level of significance (a=0.1) was also performed between
polar bear SAM-ZM 35814, polar bear AM M42656 and
Table 1 Bite force and bite force quotient (BFQ)
Species
Body
mass
(kg)
3D bite
force canine
BFQ
canine
(3D)
Asian bear 91.03 1217.39 154
Black bear 124.47 2016.94 210
Brown bear 213.68 2795.56 207
Giant panda 110.45 2603.47 292
Polar bear SAM-ZM 35814 187.27 1969.72 159
Polar bear AM M42656 226.55 2569.57 184
Agriotherium africanum 317.22 4566.14 265
3D, three-dimensional.
C. C. Oldfield et al. Cranial mechanics of bears
Journal of Zoology 286 (2012) 163–170 © 2011 The Authors. Journal of Zoology © 2011 The Zoological Society of London 165

other specimens to determine whether these were statistically
more similar to each other than to the rest of the group.
Results
Bite force
In absolute terms, bite force at the canines is greatest in A. af-
ricanum (4566 N) and least in the Asian bear (1217 N). Bite
force adjusted for body mass (bite force quotient, BFQ) was
much higher in A. africanum and the giant panda than in any
other species/specimens (Table 1). Lowest values for BFQ
were for the Asian bear and the polar bear.
Strain
For each model, we extracted mean VM brick strain data
using Strand7 (version 2.4.4). The top 5% of data was disre-
garded because particularly high values present in restrained
areas were clearly artefactual.
Intrinsic loads
Bilateral canine
From inspection of visual plots for scaled models with muscle
recruitment adjusted to produce the same bite reaction force,
the broad distributions of VM strain were similar across
species for bilateral canine bites (Fig. 2). Mean brick VM
strain in canine biting was lowest in A. africanum and the giant
panda and highest in the polar bear specimens (SI Table S4).
From two-factor ANOVA at 1% level of significance
(a=0.01) for a canine bite, P-values of 1.152 ¥10-06 (across
species) show significant mean VM brick strain variation
between species.
P-values obtained from a two-factor ANOVA shows that
at 10% level of significance (a=0.1), P<afor all possible
pairs of polar bears and other species, except between the two
polar bear specimens (Table 2). This suggests that the mean
VM brick strain distributions in the two polar bears are far
more similar to each other than to any other specimen/species.
Figure 2 Scaled to surface area, bilateral canine bite: (a) Agriotherium africanum, (b) Asian bear, (c) black bear, (d) brown bear, (e) giant panda, (f) polar
bear SAM – ZM 35814 and (g) polar bear AM M42656.
Cranial mechanics of bears C. C. Oldfield et al.
166 Journal of Zoology 286 (2012) 163–170 © 2011 The Authors. Journal of Zoology © 2011 The Zoological Society of London

Unilateral molar
Both peak and mean brick strains were lowest for A. africa-
num. The next lowest values were evident in the giant panda
(SI Table S5), followed by the black bear, both polar bears
and the Asian bear.
Extrinsic loads
Visual plots for extrinsic cases also showed similar broad dis-
tributions of VM strain across species (Fig. 3 and SI Fig. S2).
However, again there were marked differences between species
in plots for mean and maximum strain.
Pull back
Maximal and mean brick VM strain was low in both A. afri-
canum and the giant panda. For A. africanum, see SI Table S6.
Overall rankings of performance based on mean VM brick
strain data were similar to those calculated for intrinsic
loadings.
Lateral shake
Similar relative rankings were also found under shake loading
(Fig. 3) to that of the pull back loading case (SI Fig. S2). The
giant panda had the lowest mean VM strain distribution,
followed by A. africanum (SI Table S7).
Discussion
At 4566 N, our 3D bilateral canine bite force estimate for
A. africanum is the highest predicted for any mammal, being
considerably greater than the equivalent for a very large male
African lion (Panthera leo) (Wroe, 2008). A. africanum also
had a very powerful bite for its size as indicated by a high BFQ
value (Table 1).
Although our results are consistent with the suggestion that
the giant panda is well-adapted to both generate and resist
high bite reaction forces at the molars, they do not support the
contention that it is better adapted to resist high reaction
forces generated at the molars than at the canines. Only A. af-
ricanum shows lower mean and maximal VM strains under
bilateral canine loading.
Results also suggest that the polar bear is not only less
well-adapted to dispatch and eat large prey than the brown
bear (Slater et al., 2010), but that it is among the poorest
performers. Under almost all loadings, mean and maximal
VM strain values between the two polar bear specimens are
closer to each other than to any other species. This is sup-
ported by the results of pairwise two-factor ANOVA. Table 2
shows that at a=0.1, P<afor all possible pairs of polar
bears and other species, except between polar bear (SAM-ZM
35814) and polar bear (AM M42656), suggesting that the
mean VM brick strain distributions in the two polar bears are
statistically similar.
Our finding that the polar bear is arguably the poorest
performer is surprising given its status as the only living hyper-
carnivorous ursid. Our results agree with a recent analysis.
(Slater et al., 2010), which compared the mechanics of a polar
bear cranium with those of a brown bear, from which polar
bears have recently diverged (Lindqvist et al., 2010). We
suggest that the skull biomechanics of the polar bear, which
primarily ingests easily processed blubber (Perry, 1966), are
consistent with predation upon relatively small prey. More-
over, its primary prey is semiaquatic and poorly equipped to
resist capture on land.
Regarding diet in A. africanum, it was clearly capable of
generating very high bite forces for its size, and its skull was
well-adapted to resist both these and relatively high extrinsic
loads, and these are features that would be expected in a
species that regularly kills and/or scavenges on relatively large
prey. However, our results also show that the exclusively her-
bivorous giant panda is similarly well-adapted to sustain rela-
tively high loadings, indicating that ursid feeding behaviour
cannot be predicted on the basis of our FEA alone. Many
craniodental variables have been considered by previous
authors. Relative grinding area (RGA) is perhaps the most
reliable indicator of the relative importance of plant material
in the diet, with low values correlating with decreased reliance
on plants (Sacco & Van Valkenburgh, 2004). On this basis, it
is unlikely that similarities in mechanical performance
between the A. africanum and the giant panda are a conse-
quence of similarities in diet. We calculate a value of 1.47 for
RGA in our specimen of A. africanum, well below values for
RGA evidenced in any living bears, the next lowest being 1.83
in the polar bear (Van Valkenburgh, 1989).
Relative carnassial blade length (RBL) has also been
regarded as a strong indicator of the importance of vertebrate
prey in carnivoran diets, and RBL in A. africanum is also
considerably higher than in extant bears. However, among
extant bears, the only hypercarnivore that has relatively short
carnassial blades is the polar bear (Sacco & Van Valkenburgh,
2004), perhaps because it feeds mostly on blubber as opposed
to meat or bone (Perry, 1966), as previously mentioned.
No living ursids occupy niche spaces similar to those
previously hypothesized for A. africanum, that is either a
Table 2 P-values obtained from pairwise two-factor without replication
analysis of variance on mean von Mises brick strain data for five regions
in the skull under a bilateral canine load case
Polar bear
SAM-ZM
35814
Polar bear
AM M42654
Asian bear 0.023 0.078
Black bear 0.033 0.030
Brown bear 0.072 0.088
Giant panda 0.013 0.014
Agriotherium africanum 0.009 0.0189
Polar bear SAM-ZM 35814 X 0.361
Polar bear AM M42654 X
At 10% level of significance (a=0.1), P<afor all possible pairs of
polar bears and other species, except between the two polar bear
specimens.
C. C. Oldfield et al. Cranial mechanics of bears
Journal of Zoology 286 (2012) 163–170 © 2011 The Authors. Journal of Zoology © 2011 The Zoological Society of London 167

hypercarnivorous active predator of relatively large terrestrial
prey, or a scavenger of large terrestrial vertebrate carcasses
that included less plant and non-vertebrate food than most
living bears, but was nonetheless omnivorous. However, it is
perhaps notable in this context that the brown bear is the next
closest in overall mechanical performance to A. africanum
aside from the giant panda. The brown bear is the only extant
bear, which at least in part of its range, does include substan-
tial quantities of large terrestrial vertebrate prey in its diet,
killed and scavenged.
Our FEA-based results of skull mechanics do not conclu-
sively resolve the question of dietary niche for A. africanum.
However, our findings do strongly support the view that A. af-
ricanum was capable of delivering and sustaining extremely
powerful bites.
As such, our findings suggest that both major competing
hypotheses are tenable on the basis of cranial mechanics.
A. africanum was more than capable of dispatching very large
vertebrate prey, but this does not mean that it did. Likewise, in
a role as scavenger on large vertebrate carcasses, A. africanum
would have been well-equipped, with both a very high poten-
tial bite force and the craniomandibular strength to resist high
reaction forces. A more detailed FEA of heterogeneous ursid
models, including multi-property detail for dental morphol-
ogy, may help resolve which of these two proposed roles are
more likely.
Acknowledgements
This work was funded by an Australian Research Council
Discovery Project grant (DP0986471) Discovery Project
(DP0987985) and University of New South Wales Goldstar
grants to S. W. We thank Sandy Ingelby (Australian Museum)
for providing access to several specimens, and Eleanor Cun-
ningham (Newcastle Mater Hospital) for CT scanning of
these. The CT scanning of the IZIKO South African Museum
specimens was funded by a Palaeontological Scientific Trust
grant to P. D. S. and a National Research Foundation African
Origins Platform grant (AOP/West Coast Fossil Park) to R.
Smith (Iziko SA Museum). P. D. S. thanks Denise Hamerton
Figure 3 Lateral shake loading case: (a) Agriotherium africanum, (b) Asian bear, (c) black bear, (d) brown bear, (e) giant panda, (f) polar bear SAM-ZM
35814 and (g) polar bear AM M42656.
Cranial mechanics of bears C. C. Oldfield et al.
168 Journal of Zoology 286 (2012) 163–170 © 2011 The Authors. Journal of Zoology © 2011 The Zoological Society of London

for the loan of the Iziko South African Museum specimens
and N. Peters (Groote Schuur Hospital) for CT scanning
assistance. Thanks are due to H. Richards for assistance with
writing code used to perform statistical analysis, and finally,
we thank M. McCurry and C. Walmsley for providing insight
into the methods of model preparation.
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Supporting information
Additional Supporting Information may be found in the
online version of this article:
Figure S1. A phylogeny of the bear family (Ursdiae),
based upon summaries by (15) and (16). Living species are
shown in red, fossil species in magenta. Thick lines denote
known fossil record; thin lines represent relationships as deter-
mined from DNA [red lines (16)] and morphology [magenta
(15)]. Subfamilies are shown in black text at their respective
‘stem’ branches. Axis at right shows geological epochs and
dates for boundaries in millions of years. The earliest fossil
record of the primitive ursid Ursavus is 23 million years. Note
that the position of the Agriotherium within the bear family is
currently uncertain.
Figure S2. Pull back load case (A) A. africanum, (B)
Asian bear, (C) black bear, (D) brown bear, (E) giant panda,
(F) polar bear and (G) polar bear AM M42656.
Table S1. Details of finite element models and corre-
sponding CT data.
Table S2. 2D force, number of beams and pre tension
applied to beams at natural size.
Table S3. Mean von Mises microstrain values calculated
from 95% of all strain data.
Table S4. Rankings of mean VM microstrain based on
95% of strain data for a bilateral canine bite. A rank of 1 has
the highest strain and a rank of 7 has the lowest.
Table S5. Rankings resultant of mean VM microstrain of
95% of all strain data. A rank of 1 has the highest strain and
a rank of 7 has the lowest.
Table S6. Maximum and mean VM microstrain of pull
back loading case. A rank of 1 has the highest strain and a
rank of 7 has the lowest.
Table S7. Maximum and mean VM microstrain during
lateral shake loading. A rank of 1 has the highest strain and a
rank of 7 has the lowest.
Please note: Wiley-Blackwell is not responsible for the content
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authors. Any queries (other than missing material) should be
directed to the corresponding author for the article.
Cranial mechanics of bears C. C. Oldfield et al.
170 Journal of Zoology 286 (2012) 163–170 © 2011 The Authors. Journal of Zoology © 2011 The Zoological Society of London