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Bite force and encephalization in the Canidae (Mammalia: Carnivora)


Abstract and Figures

The ways in which the taxonomic differences in morphology, behavior or life history relate to each other have been used regularly to test ideas about the selective forces involved in their evolution. Canid species vary significantly in diet, hunting techniques, sociality and cranial morphology. The main goal of this study is to test and explore the possible correlation between bite force and brain volume in canids. For that, we calculated the bite force based on the beam theory, and the brain volume based on three cranial measurements. The species with biggest values of bite force quotient (BFQ) were Speothos venaticus (162.25), Cuon alpinus (129.24) and Lycaon pictus (124.41) due to several adaptations acquired along with hypercarnivory. Species with the highest values of brain volume quotient (BVQ) were S. venaticus, Cu. alpinus and L. pictus with, respectively, 141.35, 139.01 and 131.61, possibly due to the same adaptations that resulted in their bigger BFQ. The highest values of bite force belonged to Canis lupus (830.51 Pa), L. pictus (719.03 Pa) and Ca. rufus (530.52 Pa) and the smallest values belong to Urocyon littoralis (98.14 Pa), Vulpes macrotis (92.53 Pa) and V. zerda (72.6 Pa). Ca. lupus, L. pictus and Chrysocyon brachyurus possess the largest brain volumes with respectively 159.29, 146.94 and 120.84 mm3 and the smallest values belong to Nyctereutes procyonoides (28.2 mm3), V. rueppelli (27.86 mm3) and V. zerda (20.65 mm3). The independent contrasts correlation showed that there is no correlation between BVQ and BFQ (r = 0.14/P = 0.46), as well as no correlation between BFQ and BF (r = 0.22/P = 0.26), which indicates the efficiency of the size correction. Bite force and brain volume estimates are much higher in the group hunting hypercarnivores (Lycaon, Cuon and Speothos) and only these showed correlation between BFQ and BVQ. Our results indicate that cranial adaptations for hypercarnivory also influence braincase size.
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Bite force and encephalization in the Canidae
(Mammalia: Carnivora)
E. M. Damasceno1,3, E. Hingst-Zaher2& D. Astúa1
1 Department of Zoology, Universidade Federal de Pernambuco, Recife, Brazil
2 Museu Biológico, Instituto Butantan, São Paulo, Brazil
3 Faculty of Life Sciences, University of Manchester, Manchester, UK
brain volume; sociality; skull adaptations;
independent contrasts; hypercarnivory.
Diego Astúa, Av. Prof. Moraes Rego s/n,
Dept. Zoologia – Centro de Ciências
Biológicas, Cidade Universitária, Recife-PE
50670-420, Brazil
Editor: Andrew Kitchener
Received 22 May 2012; revised 30 January
2013; accepted 13 February 2013
The ways in which the taxonomic differences in morphology, behavior or life
history relate to each other have been used regularly to test ideas about the
selective forces involved in their evolution. Canid species vary significantly in diet,
hunting techniques, sociality and cranial morphology. The main goal of this study
is to test and explore the possible correlation between bite force and brain volume
in canids. For that, we calculated the bite force based on the beam theory, and the
brain volume based on three cranial measurements. The species with biggest
values of bite force quotient (BFQ) were Speothos venaticus (162.25), Cuon alpinus
(129.24) and Lycaon pictus (124.41) due to several adaptations acquired along
with hypercarnivory. Species with the highest values of brain volume quotient
(BVQ) were S. venaticus,Cu. alpinus and L. pictus with, respectively, 141.35,
139.01 and 131.61, possibly due to the same adaptations that resulted in their
bigger BFQ. The highest values of bite force belonged to Canis lupus (830.51 Pa),
L. pictus (719.03 Pa) and Ca. rufus (530.52 Pa) and the smallest values belong to
Urocyon littoralis (98.14 Pa), Vulpes macrotis (92.53 Pa) and V. zerda (72.6 Pa).
Ca. lupus,L. pictus and Chrysocyon brachyurus possess the largest brain volumes
with respectively 159.29, 146.94 and 120.84 mm3and the smallest values belong to
Nyctereutes procyonoides (28.2 mm3), V. rueppelli (27.86 mm3) and V. zerda
(20.65 mm3). The independent contrasts correlation showed that there is no cor-
relation between BVQ and BFQ (r =0.14/P=0.46), as well as no correlation
between BFQ and BF (r =0.22/P=0.26), which indicates the efficiency of the size
correction. Bite force and brain volume estimates are much higher in the group
hunting hypercarnivores (Lycaon,Cuon and Speothos) and only these showed
correlation between BFQ and BVQ. Our results indicate that cranial adaptations
for hypercarnivory also influence braincase size.
In mammals, bite strength is directly related to diet and
feeding behavior (Huber et al., 2005; Santana & Dumont,
2009), and especially so in carnivores, in which the skull and
mandible must resist the external forces generated by their
prey attempting to escape the attack (Thomason, 1991)
and thereafter, subduction and dismemberment of the kill
(Therrien, 2005; Carbone, Teacher & Rowcliffe, 2007;
Christiansen, 2007). Bite force has been widely studied due to
its capacity to predict feeding habits and hunting behavior.
For instance, studying bite force in mammals allowed
the modeling of predatory behavior in fossil taxa (Wroe,
McHenry & Thomason, 2005), analyzing the predatory
behavior on the extant canids (Slater & Van Valkenburgh,
2009), and testing the correlation between behavior and bite
force in bats (Santana & Dumont, 2009). Bite forces have
already been calculated for several orders of mammals
(Thomason, 1991; Christiansen & Wroe, 2007; Ross et al.,
2007; Freeman & Lemen, 2008), several ursids (Christiansen,
2007; Sachetti, Cárdenas & Camacaro, 2009; Oldfield et al.,
2012), saber-toothed predators (Therrien, 2005), felids
(Sakamoto, Lloyd & Benton, 2010) and domestic dogs
(Ellis et al., 2008), but not yet for all members of the
Canidae family.
In the Carnivora, bite force is of major relevance because of
the difficulty imposed by the flesh-eating diet in capturing and
killing the prey. Estimates on carnivore bite force have been
used in ecological and paleontological studies involving diet
(Christiansen & Wroe, 2007), skull allometry (Christiansen &
Adolfssen, 2005; Bourke et al., 2008), phylogenetic variation
in felids (Sakamoto et al., 2010) and development in
juveniles of spotted hyena, Crocuta crocuta (Binder & Van
Valkenburgh, 2000).
Journal of Zoology. Print ISSN 0952-8369
Journal of Zoology •• (2013) ••–•• © 2013 The Zoological Society of London 1
Other morphological aspects are critical to the survival and
adaptation of mammals. One of these is brain volume (Sol
et al., 2004, 2008), for its association to intelligence and
cognition which are essential for living and hunting in group.
Brain volume is a morphological characteristic largely
studied in primates, but scarcely studied in carnivorans. Brain
size and volume are known to be associated with sociality
(Pérez-Barbería, Shultz & Dunbar, 2007; Shultz & Dunbar,
2010) and cognitive skills (Sol et al., 2004; Deaner et al., 2007;
González-Lagos, Sol & Reader, 2010) in primates. Likewise,
relations between brain size, diet and mating have been
explored in the Order Carnivora (Gittleman, 1989), as well as
correlations between encephalization and sociality (Finarelli
& Flynn, 2009). Also, in felids, the relationships between bite
forces, skull shape and brain size were tested (Christiansen,
2008). So far, this relation has been tested only for extinct
canids (Finarelli, 2008).
Canids are particularly interesting for the study of bite
force and encephalization. Their diets and hunting methods
vary widely, ranging from species that feeds solitarily on
insects, like the bat-eared dog, Otocyon megalotis (Clark,
2005), to hypercarnivore species that hunt in packs, such as
the African hunting dog, Lycaon pictus (Malcom, 1999).
Hunting techniques are intimately linked with the sociality
level in canids, as species that hunt cooperatively are also
described as the most social, and according to the ‘social
brain’ hypothesis, the most social species are also the species
with the largest brains (Dunbar, 1998). Moreover, there is a
strong correspondence between morphology and diet among
canids (Van Valkenburg & Koepfli, 1993); hypercarnivore
species have relatively deep jaws to withstand the loads
imposed by killing and feeding on large prey, larger canines
and incisors, and molar adaptations to shear in detriment of
Comparisons of skull allometries in carnivore marsupials
and members of the Order Carnivora showed that smaller
brains allow more room for primary jaw adductors and vice
versa (Wroe & Milne, 2007). That observation led to the
hypothesis that eutherian carnivores sacrificed a stronger bite
(when compared to marsupial carnivores) for a larger brain.
Because canids present such wide variation in diet and social
behavior, the main goal of this work was to find out whether
this hypothesis holds in a lower taxonomic level, within the
Canidae family. Therefore, we tested if species of wild dogs
with bigger braincases also had the weakest bites.
Examined material
In order to estimate bite force, we took measurements from
skull images of 32 species of Canidae (Supporting Information
Table S1), representing over 90% of living groups. Every
genus of the subfamily Caninae and almost all species of each
genus were sampled (Tedford, Taylor & Wang, 1995). We
digitally photographed the skulls from three views: for the
dorsal and ventral view images, we aligned the palate with the
auditory bullae parallel to the camera and on the lateral view
aligning the midsagittal plane parallel to the camera. Every
picture had a ruler as a scale. Then, we digitized landmarks on
the images and used them to measure the distances and the
areas necessary for posterior calculations using TpsDig 2 soft-
ware (Rohlf, 2006).
Bite force
We calculated bite force estimates based on the beam theory
(Thomason, 1991) which uses the estimated cross-sectional
areas of the following muscles: m. masseter/m. pterygoideus
and m. temporalis (T), as well as the distances between the
centroids of these areas and of the temporomandibular joint
(TMJ) and the distance from TMJ and the bite force output
(in this case, the canines), which corresponds to the moment’s
arm or lever (c). All distances and areas are presented in
Fig. 1.
The muscles areas (M and T) are multiplied by 300 Kpa
(0.3 N mm-2), the estimated force applied by mammalian
muscle (Weijs & Hillen, 1985), and by the distances between
its centroids and TMJ (dm and dt). Afterwards, they were
added together and multiplied by two to equal both sides of
the skull. This total value, divided by the moment’s arm (c)
equals the ‘absolute’ bite force (F).
FM KPa dt T KPa
+× ×
2 300 300dm
Bite forces calculated through dry skulls usually underesti-
mate bite forces measured in vivo, so Thomason’s (1991)
correction method must be applied. Even though this method
was heavily criticized by numerous authors (Christiansen &
Adolfssen, 2005; Wroe & Milne, 2007) for not fitting to bigger
species, Thomason’s correction method was recently tested in
predators whose body weight resembles canids and was
proved to be efficient (Sakamoto et al., 2010). The correction
method consists on the formula:
Fcorr logF
10 0 859 0 559,,
Due to the great influence of body size on bite force (van
der Meij & Bout, 2004; Christiansen & Adolfssen, 2005; Wroe
et al., 2005), and because canids vary greatly in size, a size
correction is also necessary. We used skull length (measured
directly on each photograph used for bite force calculations)
as body size estimators, as actual body weight information
was not available for all specimens. Skull length represent the
best skeletal predictors for mass in canids (Van Valkenburgh,
1990). We regressed (using simple linear regression) the loga-
rithm of corrected bite force on the logarithm of each speci-
men skull length (Fig. 1). This analysis generated a function
used to calculate bite force based on skull length (FL):
10 195 112,,
This step needs to be done with the actual data, as the
result of the regression needs to be expressed in terms of
the original variables, to be used in subsequent steps.
Bite force and encephalization in canids E. M. Damasceno, E. Hingst-Zaher and D. Astúa
2Journal of Zoology •• (2013) ••–•• © 2013 The Zoological Society of London
Additionally, Sakamoto et al. (2010) argued that the actual
individual data (and not species means) need to be used in this
step. However, in order to rule out any effect due to non-
independence of data because of common ancestry, we
repeated this same regression using species mean, with and
without the use of a phylogenetic comparative method. Here,
we used phylogenetic independent contrasts (PICs) (Harvey &
Pagel, 1991). Calculations of PICs and diagnostic procedures
were performed with the PDAP:PDTree module (Midford,
Garland Jr & Maddison 2005) of Mesquite (Maddison &
Maddison, 2007), using the phylogenetic hypothesis of Perini,
Russo & Schrago (2010) (but see below, correlation analyses,
for further details on phylogeny choice). Results from these
two regressions were similar (Bite force and skull length with
contrasts, r =0.88/P<0.001 and without contrasts r =0.96/P
=0.001; brain volume and skull length with contrasts, r =
0.89/P<0.001 and without contrasts r =0.96/P=0.002),
indicating no major effect of the phylogenetic relationships
between species in this relation, thus enabling us to use the
results from the regression using individuals in the subsequent
Next, we calculated bite force quotient (BFQ). It is the
proportion between corrected bite force and skull length
based bite force (Sakamoto et al., 2010).
The quotient is not a force value (Pa), it is a proportion
where body size influence is absent (Sakamoto et al., 2010).
Brain volume
We estimated brain volume following Finarelli (2006), using
the natural logarithm of three external skull measurements:
height (H), length (L) and width (W) (Fig. 1). Finarelli’s
method is appropriate because the measures used neurocra-
nium external dimensions along three orthogonal axes. They
correspond approximately to measures previously used to esti-
mate cranial volume in primates (e.g. Martin, 1990; Elton
et al., 2001) and are consistent with three cranial measures
used by Young (1959) to define intracranial dimensions
(Finarelli, 2006).
Ln ln H ln L ln W
brainvol.,,. ,. ,.
=− +
623 106 028 127
After calculating brain volume, we performed a simple
linear regression between the log of brain volume and log of
skull length, which generated the following function.
Log log
brainvol length(.) ()
,. ,=−1 7501 2 0889
After obtaining the brain volume estimated through skull
length, we generated a size influenced value. In order to
remove this influence we calculated the proportion between
‘absolute’ brain volume (estimated through the three skull
measurements) and the volume based on skull length (bvlength).
This proportion is called brain volume quotient (BVQ) which
is calculated through the formula:
BVQ brainvol
Correlation analyses
We tested the correlation between the ‘absolute’ and quotient
values of bite forces and brain volumes. Again, to account for
non-independence of data due to common ancestry, we used
PICs (Harvey & Pagel, 1991). As above, calculations of PICs
Figure 1 Diagrams showing the areas and
distances used to calculate bite forces
and brain volume. Variables for bite force
estimates: M, cross-sectional areas of mus-
culus masseter; T, cross-sectional areas of
musculus temporalis muscles; dm, distance
between the centroid of M and temporoman-
dibular joint (TMJ); dt, distance between the
centroid of T and TMJ; c, distance between
bite point (canine) and TMJ. Variables for brain
volume estimates: H, skull height; L, skull
length; W, skull width.
E. M. Damasceno, E. Hingst-Zaher and D. Astúa Bite force and encephalization in canids
Journal of Zoology •• (2013) ••–•• © 2013 The Zoological Society of London 3
and diagnostic procedures were performed with the PDAP:P-
DTree module (Midford et al., 2005) of Mesquite (Maddison
& Maddison, 2007). We used here three phylogenetic hypoth-
eses: Lindblad-Toh et al. (2005), Prevosti (2009) and Perini
et al. (2010). Branch lengths, however, were only available in
the latter, and these went through Grafen’s transformation
method, with rho (r) value of 0.5 to decrease the chances of
type I error and suit the variables according to independent
contrasts method (Grafen, 1989; Díaz-Uriarte & Garland Jr
1996). For the two others, we used branch lengths of one, and
these two we mainly included for comparison purposes on the
effect of phylogeny topology and taxon sampling on our con-
clusions. In all cases, all variables passed the diagnostics, i.e.
showed no correlation between absolute contrasts and their
standard deviations after being log-transformed and after
Grafen’s transformation method.
Bite force and brain volume estimates
Results of bite force calculations and brain volume estimates
are presented in Table 1.
Correlation analyses
We found a strong and significant correlation between bite
force and brain volume in all phylogenies. However, BFQ and
BVQ are uncorrelated when using the topology and branch
lengths (Perini et al., 2010), yet they are weakly correlated
when using the phylogenies from Lindblad-Toh et al. (2005)
and Prevosti (2009) (Table 2).
Table 1 Taxa analyzed with bite force quotient (BFQ) values, corrected bite force, brain volume quotient (BVQ), corrected brain volume and the
sample size (n) for every species. See text for details
Species/subspecies Bite force BFQ Brain volume BVQ n
Alopex lagopus (Linnaeus, 1758) 140.61 88.41 40.04 101.31 37
Atelocynus microtis (Sclater, 1882) 312.12 106.66 70.55 101.81 21
Canis adustus (Sundevall, 1847) 248.69 86.71 62.57 94.71 30
Ca. aureus (Linnaeus, 1758) 254.69 93.82 64.01 101.58 30
Ca. simensis (Ruppel, 1835) 413.39 83.96 88.10 85.57 8
Ca. familiaris dingo (Meyer, 1793) 494.48 113.28 92.24 102.23 33
Ca. familiaris hallstromi (Troughton, 1957) 298.52 108.50 66.33 113.38 6
Ca. latrans (Say, 1823) 397.10 94.02 90.54 100.19 30
Ca. lupus (Linnaeus, 1758) 830.51 106.14 159.29 107.18 30
Ca. mesomelas (Schreber, 1775) 243.41 97.64 58.06 98.55 30
Ca. rufus (Audubon e Bachman, 1851) 530.52 99.17 102.98 92.96 6
Chrysocyon brachyurus (Illiger, 1815) 525.54 98.86 120.84 104.10 22
Cuon alpinus (Pallas, 1811) 497.74 129.24 110.88 139.01 20
Cerdocyon thous (Hamilton Smith, 1839) 184.16 99.1 48.82 96.72 32
Lycalopex fulvipes (Martin, 1837) 182.93 112.21 34.41 91.92 2
L. vetulus (Lund, 1842) 125.14 104.23 37.77 104.26 18
L. culpaeus (Molina, 1782) 281.57 99.25 63.30 93.34 31
L. griseus (Gray, 1837) 154.29 88.07 41.76 100.01 30
L. gymnocercus (Fischer, 1814) 190.32 89.88 47.66 86.65 30
L. sechurae (Thomas, 1900) 168.33 106.95 34.66 89.06 30
L. pictus (Temminck, 1820) 719.03 124.41 146.94 131.61 30
Nyctereutes procyonoides (Gray, 1834) 147.29 109.01 28.20 81.74 30
Otocyon megalotis (Desmarest, 1822) 111.64 87.25 32.24 91.65 30
Speothos venaticus (Lund, 1842) 287.88 162.25 65.48 141.35 21
Urocyon cinereoargenteus (Schreber, 1775) 136.97 100.64 36.58 102.76 39
U. littoralis (Baird, 1858) 98.14 95.63 30.96 115.74 30
Vulpes zerda (Zimmerman, 1780) 72.60 97.10 20.65 101.84 30
V. bengalensis (Shaw, 1800) 139.85 114.13 33.51 104.17 10
V. chama (Smith, 1833) 136.21 91.49 47.75 130.83 19
V. macrotis (Merriam, 1888) 92.53 86.40 30.76 107.25 21
V. pallida (Cretzschmar, 1827) 103.31 96.96 30.72 112.32 19
V. rueppelli (Schinz, 1825) 114.39 91.35 27.86 83.60 30
V. velox (Say, 1823) 134.36 96.50 34.60 101.10 14
V. vulpes (Linnaeus, 1758) 224.27 91.46 52.74 97.69 32
Bite force and encephalization in canids E. M. Damasceno, E. Hingst-Zaher and D. Astúa
4Journal of Zoology •• (2013) ••–•• © 2013 The Zoological Society of London
Bite force and brain volume estimates are much higher in the
group hunting hypercarnivores (Lycaon,Cuon and Speothos)
and only these species showed correlation between BFQ and
BVQ. The bite force quotient values seem to be related with
skull morphology, as well as BVQ results that also point at a
tighter association with skull morphology than with ecological
characteristics. The ‘absolute’ values, on the other hand,
showed the expected pattern, with the highest values for the
biggest species and the lowest values for the smallest species,
just as presented in Christiansen & Adolfssen (2005).
Bite force quotient
The species with the highest values of BFQ are the three
hypercarnivore canids (Speothos venaticus, Cuon alpinus,
L. pictus). When compared to all other canids, hypercarni-
vores have relatively wider snouts (Fig. 2), more mechanical
advantages on the jaw adductors, deeper jaws (Fig. 3), larger
anterior teeth (incisive and canine), reduced crushing post-
carnassial molars, elongated blades (trigonid) on the inferior
m1 (Gittleman, 1989; Van Valkenburgh, Wang & Damuth,
2004). In the bush dog, African wild dog and the dhole, the m1
talonid has also become a blade or trenchant heel, which
increases the cutting ability.
Several of these characters can increase hunting efficiency,
and are also useful for knocking down prey, resisting bending
forces and cutting flesh. But one main feature that consider-
ably increases bite force is tooth row reduction, through the
loss of post-carnassial molars (Van Valkenburgh, 2007). This
is found in other hypercarnivore groups, such as cats and
mustelids (Radinsky, 1981). In general, canids have two upper
and three lower molars, but bush dogs have in most cases only
one upper (91.5%) and two lower molars (Beisiegel & Zuecher,
2005), dholes only have two upper and two bottom molars
(Cohen, 1978) and African wild dogs have two upper and
three bottom molars.
Even though wolves have a hypercarnivore diet and hunt
preys that are heavier than themselves (Hammer, Harper &
Ryan, 2001; Van Valkenburgh, 2007), they do not present a
BFQ value similar to the other hypercarnivore species. A pos-
sible reason for this is that wolves do not present morphologi-
cal adaptations as marked as in the other hypercarnivorous
The species with the lowest BFQ values are side-striped
jackals (Canis adustus), kit foxes (Vulpes macrotis), Ethiopian
wolves (C. simensis) and bat-eared foxes (O. megalotis). Even
though these species are not related phylogenetically nor
resemble each other in external morphology, they all live in
desert-like environments. For that reason, they all are oppor-
tunistic feeders, feeding on anything that is most abundant,
small rodents, reptiles, ground-nesting birds (McGrew, 1979;
Sillero-Zubiri & Gottelli, 1994). The only exception is the
bat-eared fox that is mainly insectivorous, feeding on termites,
beetles, crickets and grasshoppers (Clark, 2005), presenting a
slender, delicate skull with 4–5 molars, basically, the opposite
skull morphology from hypercarnivores.
Brain volume quotient
Species with the highest BVQ values were the hypercarnivores
bush dog, the dhole and the African wild dog (Table 1). The
social brain hypothesis (Dunbar, 1998) states that species that
present social behavior have bigger brains. Nevertheless, the
grey wolf (a highly social species) had its BVQ values ranked
only in 10th position, not only lower than the other social
species, but below four species of non-social foxes. Based on
these results, we can speculate that Speothos,Cuon and
Lycaon have the highest values of BVQ because they are
hypercarnivorous species.
These results suggest that the BVQ is not linked exclusively
to sociality in the pack-hunting species, but is mainly related
to skull shape, in Speothos,Cuon and Lycaon as they have
Table 2 Values for Pearson’s correlation coefficient (r) and significance (P) for the correlation analyses between bite force quotient (BFQ), brain
volume quotient (BVQ), bite force (Bf) and brain volume (Bvol) for all the phylogenies used
r (p) Lindblad-Toh et al. (2005) Prevosti (2009) Perini et al. (2010)
BFQ ¥Bf -0.03 (0.85) -0.044 (0.83) 0.22 (0.26)
BVQ ¥Bvol 0.22 (0.24) 0.055 (0.78) 0.26 (0.18)
BFQ ¥BVQ 0.57 (0.001) 0.65 (<0.001) 0.14 (0.46)
Bf ¥Bvol 0.90 (<0.001) 0.83 (<0.001) 0.98 (<0.001)
Figure 2 Ventral view of the skulls of Speothos venaticus and Vulpes
pallida, representing hypercarnivores and hypocarnivores, respectively.
E. M. Damasceno, E. Hingst-Zaher and D. Astúa Bite force and encephalization in canids
Journal of Zoology •• (2013) ••–•• © 2013 The Zoological Society of London 5
similar skull morphologies. This indicates that adaptive con-
vergences that increased bite force also increased brain
volume. For example, a wider occipital bone results in larger
braincase and also stronger neck muscles, thus giving consid-
erable resistance to lateral loadings such as a struggling prey
(Radinsky, 1981).
Correlation analyses
The correlation analyses between BVQ and BFQ yielded dif-
ferent results between the phylogeny of Perini et al. (2010),
with branch lengths, and those of Prevosti (2009) and
Lindblad-Toh et al. (2005), both with branch lengths arbitrar-
ily assigned to one. While the former indicated no correlation
between the studied variables, the latter two showed a signifi-
cant, albeit weak (r2ranging from 0.32 to 0.42) correlation
(Table 2). Proper branch lengths, either as evolutionary rates
or as divergence times, are essential for an appropriate use
of phylogenetic comparative analysis. Phylogenies without
branch lengths tend to increase type I error rates (rejection
of a true null hypothesis) (Purvis & Rambaut, 1995;
Díaz-Uriarte & Garland Jr 1996). They are therefore less reli-
able, and as a consequence, we will only consider the results
that used the phylogeny of Perini et al. (2010), and will only
discuss these further on.
A weak correlation was found between the quotients and its
respective absolute values, indicating that a significant correc-
tion was achieved by the quotients. Body size influence was
observed due to strong correlation between bite force and
brain volume and absence of correlation between their quo-
tients (Table 2).
There was no correlation between BFQ and BVQ, even
though the three highest values of BFQ are also the highest
values of BVQ. This shows that in spite of being linked to
morphology, both variables are independent in the Canidae
family. The morphological difference and therefore differ-
ences in both force and brain volume are much more con-
spicuous among Lycaon+Cuon+Speothos group and the other
canids than among the family itself. Hence, BFQ and BVQ
calculus was efficient in pointing out and differentiating pack-
hunting hypercarnivores, but it did not set apart among the
remaining species, the most carnivores from the least carni-
vores nor the solitary from the social species. In other words,
bite force and brain volume correlate only among the hyper-
carnivores. These results agree with analysis in insectivores
and primates that show correlation between dietary speciali-
zation with increase in encephalization (Bauchot and Stephan
1966, 1969 apud Gittleman 1986). Other studies involving
active consumption rates (ACR) found a positive correlation
between ACR and sociality (Wilmers & Stahler, 2002). In
situations where fast ingestion is favored, for example,
between cubs from the same litter or adults feeding commu-
nally from the same kill, selection shall favor those with
sharper teeth and strongest bite (Van Valkenburgh 1991; Van
Valkenburgh, 2007).
When eutherian and metatherian carnivores were com-
pared, brain volume and bite force were negatively corre-
lated (Wroe & Milne, 2007). In canids, however, species with
bigger brains also have stronger bites. This could mean that
a large braincase also gives room for large and longer
m. temporalis, that is the most important mandibular adduc-
tor in the carnivoran skull. In marsupials and placental
mammals, in order to achieve stronger bites, species must
sacrifice brain volume to increase muscles involved in biting.
When compared throughout the Canidae, hypercarnivore
canids possess stronger bite forces than all other meso and
hipocarnivore species. But when compared with hypercarni-
vores of other families (such Felidae, Mustelidae and Dasyu-
ridae), hypercarnivore canids cannot achieve equivalent bite
forces (Wroe et al., 2005). This could possibly be because
bigger brain volume in canids could not allow such an
extreme change in skull morphology, as it has been sug-
gested that canids need this bigger brain for cognitive
development, in order to master complex social behaviors
(Dunbar, 1998).
Bite force and brain volume are related to body size and
should therefore be corrected for size in any subsequent analy-
sis. BFQ is related to skull morphology, as hypercarnivore
species have the highest quotient values and the hipo and
mesocarnivores have the lowest ones. Apparently, the BVQ is
also related to skull morphology but has no relation with
sociality level of species. BFQ and BVQ are related only in its
extremes: species with the highest BFQ are also the ones with
highest BVQ are all hypercarnivores, with craniodental adap-
tations such as larger snouts and deeper jaws, which indicates
a relation between diet specialization and cranial morphology
including an increase in brain volume.
Figure 3 Lateral view of the mandibles of
Speothos venaticus and Vulpes pallida, repre-
senting hypercarnivores and hypocarnivores,
Bite force and encephalization in canids E. M. Damasceno, E. Hingst-Zaher and D. Astúa
6Journal of Zoology •• (2013) ••–•• © 2013 The Zoological Society of London
Two Brazilian financial institutions have supported this study:
Fundação de Amparo à Ciência e Pesquisa de Pernambuco
(FACEPE), through a MSc. Scholarship and a travel grant to
E.M.D., and through grants for the acquisition of the photo-
graphic material to D.A. (APQ-0351-2.04/06) and Fundação
de Amparo à Pesquisa do Estado de São Paulo (FAPESP –
01/07053-8 and 11/50206-9). We are also thankful to the fol-
lowing curators and/or collection managers for access to the
specimens under their care, help during our visits or loans:
Robert Voss, Teresa Pacheco, John Flynn and Judy Galkin
(AMNH); Bruce Patterson and Robert Fisher (NMNH) and
Eliécer Gutierrez and Alejandro Oceguera for lodging in New
York. We are grateful to Per Christiansen, Fabio de Andrade
Machado and an anonymous reviewer for suggestions that
improved the quality of this paper.
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Supporting information
Additional Supporting Information may be found in the
online version of this article at the publisher’s web-site:
Table S1 List of taxa used, their mean bite force quotient,
brain volume quotient, their classifications pertaining to diet
and sociality and the source of such information.
E. M. Damasceno, E. Hingst-Zaher and D. Astúa Bite force and encephalization in canids
Journal of Zoology •• (2013) ••–•• © 2013 The Zoological Society of London 9
... It is probably unrealistic to characterize allosaurs as specialized bloodletters with unique, weak-jawed hunting styles, either, because there is no evidence to support such an explanation. Even canids, which often kill prey by exsanguination, have very high bite force quotients along with morphologically slender canine teeth to successfully accomplish the soft tissue damage required to bleed out their targets [121,122]. Canids also have excellent binocular vision, which allows them to make precise bites into arteries and other vulnerable anatomy of their prey. Allosaurus and its carnosaurian relatives uniformly lacked the high bite force, dental adaptations, and binocular vision, that would have allowed them to consistently undertake these types of attacks. ...
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The reasons why some animals have developed larger brains has long been a subject of debate. Yet, it remains unclear which selective pressures may favour the encephalization and how it may act during evolution at different taxonomic scales. Here we studied the patterns and tempo of brain evolution within the order Carnivora and present large-scale comparative analysis of the effect of ecological, environmental, social, and physiological variables on relative brain size in a sample of 174 extant carnivoran species. We found a complex pattern of brain size change between carnivoran families with differences in both the rate and diversity of encephalization. Our findings suggest that during carnivorans' evolution, a trade-off have occurred between the cognitive advantages of acquiring a relatively large brain allowing to adapt to specific environments, and the metabolic costs of the brain which may constitute a disadvantage when facing the need to colonize new environments.
Functional requirements for different diets have a strong selective pressure leading to convergent adaptations across different groups of mammals. As body size has an influence on many biomechanical and physiological characteristics, it is logical that dietary adaptations often have a strong link to body size resulting in observed ‘size guilds’ in many diverse phylogenetic lineages. However, non‐allometric variation in skull shape may provide an alternative pathway for species to adapt to diets or prey handling by breaking the mould away from the line of least evolutionary resistance, increased body size. We investigated the relationships between cranial shape and body size in the evolutionary context of the shift from insectivory to hypercarnivory in a monophyletic group of 16 dasyurine marsupial species. Analysis of 35 Procrustes‐corrected 3D skull landmarks revealed that overall, there was a correlation between mean skull shape and size that correlated with diet. However, the dominant shape variation (almost 80% irrespective of phylogeny, and more than 90% when constrained by phylogeny) was not size‐related. This non‐allometric pattern of skull shape reveals adaptation for different feeding strategies that is independent of absolute size. This highlights the potential for specific ‘thresholds’ in size and shape to exist that have the potential to mark shifts from one dietary niche to the next, that might be applied to the evolution of carnivorous taxa from other lineages.
Understand the factors that lead morphological differentiation is a central question in evolutionary biology. The extraordinary latitudinal distribution of the fox Lycalopex culpaeus makes it a model species to investigate the causes of phenotypic divergence. We analyzed the morphological differentiation of the species from genetic analyzes using mitochondrial sequences (COI and D-loop), nuclear (FES, CHRNA1, VTN, SEIL1L3, CCDC90B, and ABCA1), and from geometric morphometric, studying two morphological structures: the skull and jaw. As the body size estimation used the size of the skull. To analyze the relative contribution of neutral and adaptive processes, were conducted correlation analyzes between each phenotypic trait and (i) the genetic structure based on neutral markers, which reflect the historical variations, (ii) environmental connectivity between populations, which shows the contemporary genetic flow restrictions and (iii) environmental variables, which may lead to local adaptation events or phenotypic plasticity. Different current and past environmental barriers were detected among populations, there is a strong genetic and morphological structuring. It was observed that the divergence of the shape of the skull is related only with the genetic structuring, being largely the result of genetic drift processes (stochastic). Moreover, the shape of the jaw showed no correlation with any of the variables analyzed, this may be due to the fact that the jaws are susceptible to homoplasies. The size of the skull showed a clear pattern of Bergmann, where larger animals were observed at higher latitudes, and negatively correlated with temperature and positively correlated with variables related to primary productivity. These results are consistent with the idea that local adaptation processes and phenotypic plasticidad have a fundamental role in the variation of the size of L. culpaeus. We demonstrated that in more than one process is responsible for the phenotypic variation in the fox L. culpaeus, giving a robust methodological framework to test the combined effects of morphological, genetic, environmental and space variables.
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The present paper deals with the ecomorphological characteristics of two sympatric species of ictitheres: Ictitherium viverrinum Roth & Wagner, 1854 and Hyaenictitherium wongii (Zdansky, 1924) from the Late Miocene of the Eastern Mediterranean. These two species represent different taxonomic groups with allegedly distinct ecological roles. The values of 11 ecomorphological proxies were calculated using cranial and dental elements, in order to make an extensive comparison between them (body mass, bite force, canines’ and incisors’ bending strength, endocranial volume, relative rostral width, dental mesowear, intercuspid notches and carnassial vs grinding surfaces). The proxies show similar results for both species, pointing out that they had a similar ecological niche in the Late Miocene ecosystems. Carnivorans are usually in the top of the food chain, so the existence of two ecologically similar species in the same spatiotemporal range results in interspecific competition. This explains the geographical distinction of the two species with several localities being dominated by only one of the two (e.g. Samos for Hyaenictitherium Kretzoi, 1938 and Pikermi for Ictitherium Wagner, 1848). The reason for the prevalence of each genus can be associated with their postcranial morphology, as Hyaenictitherium has been proposed to be better adapted to chase hunting, because of its longer limbs, while Ictitherium is characterized by shorter and stouter limbs.
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When a large body of knowledge has been produced on a group of closely related species, especially when they are becoming comparatively rare on the landscape, it is paramount that these works be easily accessible to researchers, students, and the general public. With the advent of the World Wide Web, it may seem that bibliographies are becoming obsolete, but after a brief search, an interested party will soon discover that there is no logical order behind the results they obtain. Further confusion results from searches that yield articles that are mainly opinion or conjecture rather than peer-reviewed material. In addition, it is becoming increasingly difficult to keep abreast on the emerging new literature, even when using internet search engines, because of the continual increase of potential article outlets. A concise catalog of available peer-reviewed material is necessary for any researcher wishing to extract the available information on a given species. Herein is a compilation of the large body of peer-reviewed information on two species of fox: the Kit Fox, Vulpes macrotis, and the Swift Fox, V. velox. These two foxes are closely related and are often used as umbrella species in conservation efforts of their ecosystems, which include grassland prairie and arid deserts.
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Events during the Late Oligocene of North America and the Pleistocene of South America, provide an opportunity for exploring possible causes of the evolution of hypercarnivory in canids. Plots of generic diversity gainst time for North American predators reveal a roughly inverse relationship between the number of hypercarnivorous canid taxa and the numbers of other hypercarnivores, such as creodonts, nimravids, mustelids, and amphicyonids. Similarly, the radiation of hypercarnivorous canids in South America occurred at a time of relatively low diversity of other hypercarnivores. Analysis of trophic diversity within the North American carnivore paleoguild before, during, and after the Late Oligocene reveals considerable taxonomic turnover among carnivores because of immigration and speciation. Late Oligocene hypercarnivorous canids appear to have been replaced first by amphicyonids and large mustelids, and then by felids. -from Author
Carnivores have always fascinated us, even though they make up only 10% of all mammalian genera and only about 2 % of all mammalian biomass. In Greek mythology most of the gods adorned their robes and helmets with depictions of carnivores, and the great hero Hercules' most famous feat was killing the "invulnerable" lion with his bare hands. Part of our fascination with carnivores stems from fright and intrigue, and sometimes even hatred because of our direct competition with them. Cases of "man-eating" lions, bears, and wolves, as well as carnivores' reputation as killers of livestock and game, provoke communities and govermllents to adopt sweeping policies to exterminate them. Even President Theodore Roosevelt, proclaimer of a new wildlife protectionism, described the wolf as "the beast of waste and desolation. " The sheer presence and power of carnivores is daunt­ ing: they can move quickly yet silently through forests, attaining rapid bursts of speed when necessary; their massive muscles are aligned to deliver powerful attacks, their large canines and strong jaws rip open carcasses, and their scis­ sor-like carnassials slice meat. Partly because of our fear of these attributes, trophy hunting of carnivores has been, and to a certain extent still is, a sign of bravery and skill. Among some Alaskan Inuit, for example, a man is not eligible for marriage until he has killed a succession of animals of increasing size and dangerousness, culminating with the most menacing, the polar bear.
Fifteen variables, selected primarily to reflect functionally significant aspects of cranial morphology, were measured on one skull each of 62 species of modern carnivores, including viverrids, canids, mustelids and felids. To allow comparisons between species of different sizes without the potentially confounding effects of allometric shape changes, the measurements were transformed to dimmensionless variables, based on the residuals from allometric equations. Fourteen out of 15 of the transformed variables distinguish one or more of the four family groups and the rotated first two axes of a principal components analysis distinguish all four families from each other. The following functional hypotheses are proposed: mustelids and felids have the most powerful bites and canids the weakest among the four family groups studied; mustelids and, to a lesser degree, felids have more powerful neck musculature than do canids and viverrids; and visual abilities are best developed among felids and least developed among mustelids. The first two functional hypotheses suggest possible differences in killing behaviour, which are supported by a preliminary survey of the literature on such behaviour. Allometric analysis of the 15 cranial measures shows that the neurocranial components scale with negative allometry, while most of the other measures scale approximately isometrically.
Conventional wisdom over the past 160 years in the cognitive and neurosciences has assumed that brains evolved to process factual information about the world. Most attention has therefore been focused on such features as pattern recognition, color vision, and speech perception. By extension, it was assumed that brains evolved to deal with essentially ecological problem-solving tasks. 1.