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Zoomorphology
Evolutionary, Comparative and
Functional Morphology
ISSN 0720-213X
Volume 131
Number 1
Zoomorphology (2012) 131:79-92
DOI 10.1007/s00435-012-0145-4
A quantitative approach to the cranial
ontogeny of Lycalopex culpaeus
(Carnivora: Canidae)
Valentina Segura & Francisco Prevosti
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Zoomorphology (2012) 131:79–92
DOI 10.1007/s00435-012-0145-4
123
ORIGINAL PAPER
A quantitative approach to the cranial ontogeny
of Lycalopex culpaeus (Carnivora: Canidae)
Valentina Segura · Francisco Prevosti
Received: 16 July 2011 / Revised: 30 December 2011 / Accepted: 2 January 2012 / Published online: 13 January 2012
© Springer-Verlag 2012
Abstract The study of cranial ontogeny is important for
understanding the relationship between form and function
in developmental, ecological, and evolutionary contexts.
The transition from lactation to the diet of adult carnivores
must be accompanied by pronounced modiWcations in skull
morphology and feeding behavior. Our goal was to study
relative growth and development in the skull ontogeny of
the canid Lycalopex culpaeus, and interpret our Wndings in
a functional context, thereby exploring the relationship
between changes in shape and size with dietary habits and
age stages. We performed quantitative analyses, including
multivariate allometry and geometric morphometrics. Our
results indicate that shape changes are related to functional
improvements of the jaw mechanics related for food catch-
ing/processing. Estimates of full muscle size, mechanical
advantage, and adult cranial shape are reached after sexual
maturity, while adult mandible and skull size are reached
after weaning, which is related to diet change (incorpora-
tion of meat and other food items). The ontogenetic pattern
observed in L.culpaeus is similar to those observed in
Canis familiaris and C.latrans. However, the magnitude of
change seen in L.culpaeus is smaller than those seen in the
felid Puma concolor and considerably smaller than those
seen in the bone cracker hyaenid Crocuta crocuta. These
patterns are associated with dietary habits and specializa-
tions in skull anatomy, as L.culpaeus, domestic dog and
coyote are generalist species compared with hypercarni-
vores such as C.crocuta and P.concolor.
Keywords Anatomy · Canidae · Ontogeny · Skull
Introduction
The skull is a complex structure that not only houses the
brain, but also the sense organs and muscles related to the
opening and closing of the mandible, and to food capture
and processing (Emerson and Bramble 1993; Moore 1981).
Because of its complexity, the skull has been the focus of
several ontogenetic studies in Mammalia, exploring how
adult morphology and function are achieved (e.g., Flores
et al. 2006, 2010; Giannini et al. 2004; Wayne 1986). In
this context, mammalian cranial ontogeny is relevant to
understand the relationship between form and function in a
developmental, ecological, and evolutionary context. In
carnivore species, the transition from nursing in juveniles
to a carnivorous diet in adults must be accompanied by pro-
nounced modiWcations in behavior and skull morphology
linked to diet changes and the acquisition of new hunting
methods (Binder and Van Valkenburgh 2000; Fox 1969).
Previous studies about ontogeny in canid species have
focused on behavior (e.g., BekoV 1974a, b; Biben 1982,
1983; Scott 1967), neurological responses (e.g., Fox 1964),
chronology of tooth eruption and replacement (e.g., BekoV
and Jamieson 1975; Kremenak 1969; Kremenak et al. 1969;
Communicated by T. Bartolomaeus.
Electronic supplementary material The online version of this
article (doi:10.1007/s00435-012-0145-4) contains supplementary
material, which is available to authorized users.
V. Segura (&) · F. Prevosti
División Mastozoología, Museo Argentino de Ciencias
Naturales “Bernardino Rivadavia”, Av. Ángel Gallardo 470,
CP 1405, Ciudad Autónoma de Buenos Aires, Argentina
e-mail: vsegura@macn.gov.ar; valu_z@yahoo.com.ar
V. Segura · F. Prevosti
CONICET. Consejo Nacional de Investigaciones
CientíWcas y Técnicas, Buenos Aires, Argentina
Author's personal copy
80 Zoomorphology (2012) 131:79–92
123
Prevosti and Lamas 2006), and age estimation (e.g., Zapata
et al. 1997). These works have presented some results in a
morphological or behavioral framework, although mainly
concerned with age estimation and without considering cra-
nial characters in a functional context. Some exceptions to
this are works of Wayne (1986), who studied the ontoge-
netic trajectories of skull growth in the domestic dog, Canis
familiaris Linnaeus, 1758, revealing that are morphologi-
cally diVerent than other canid species (e.g., in the latter,
neonates and adults exhibit narrower palates and zygomatic
breadth), and La Croix et al. (2011), who examined growth
and development of skull in coyotes, Canis latrans Say,
1823, detecting patterns of synchronous growth and asyn-
chronous development between skull and mandible. Drake
(2011), who investigated heterochronic patterns in the skull
morphology of C.familiaris, revealed that cranial shape of
adults not resembles the cranial shape of an ontogenetic
series of wolves, Canis lupus Linnaeus, 1758. In view of
such variations, the inclusion of other canids could reveal
other patterns of skull development.
Lycalopex culpaeus (Molina, 1782) is the largest repre-
sentative of the genus and the second largest canid species
in South America (body mass around 10 kg; Novaro 1997).
These species inhabit the semidesertic Andean plateau,
mediterranean scrub and grasslands, and woodland areas in
western and southern South America from Colombia to
southern Chile and Argentina (Novaro 1997). L.culpaeus
has a generalist diet that includes small and medium-sized
vertebrates, as well as insects and vegetables, although it is
more carnivorous and consumes larger mammalian preys
than other South American canid species (Jiménez and
Novaro 2004; Johnson and Franklin 1994). According to its
diet, L.culpaeus has a generalized/omnivore skull and den-
tition (e.g., narrow snouts and occiputs, full dentition count,
well-developed grinding regions in the molar), but its denti-
tion is more secodont (e.g., larger carnassials and cusp
reductions), and its canines are longer than those of other
Lycalopex species (Berta 1987; Kraglievich 1930; Van
Valkenburgh 1988; Van Valkenburgh and KoepXi 1993).
The pioneering work of Crespo and De Carlo (1963)
provided most of what is known about breeding and growth
in this species. The gestation period is between 55 and
60 days, young born with eyes closed, and at 2 days of age
males weigh about 166 g with a total length of 165 mm,
whereas females weigh about 170 g with 161 mm of total
length. The pups reach adult size in 7 months, and sexual
maturity is attained during the Wrst year. The pups nurse
until weaning at 2 months of age. Post-weaning, the juve-
niles are still dependent while they begin to hunt with their
parents until they are strong enough to feed for themselves
(Crespo and De Carlo 1963; Ewer 1973). Some studies
oVered morphological estimators of age (e.g., Crespo and
De Carlo 1963; Zapata et al. 1997) from 9 months of age, a
period where mature morphology is usually reached. How-
ever, these works were unable to estimate age for earlier
stages, a period deWned as critical for the morphological
change and the acquisition of adult characters. In this sense,
the ontogenetic pattern of L.culpaeus has been partially
studied to date, showing that quantitative analyses of cra-
nial allometric growth and relative shape changes, empha-
sized in crucial ontogenetic periods, are still unknown.
In this study, we performed quantitative analyses of
skull ontogeny (shape and size) of L.culpaeus, using multi-
variate allometry and geometric morphometrics. Taken
together, these approaches allowed us to study the relative
growth of the diVerent cranial components. We further
interpreted our Wndings in a functional context, exploring
the relationship between size and shape changes with life
history traits during the ontogeny of the largest South
American fox.
Materials and methods
Sample
We analyzed an ontogenetic series of 101 skulls deposited
at Museo Argentino de Ciencias Naturales Bernardino Riv-
adavia (MACN; see “Appendix 1”). The specimens belong
to the subspecies L.c.culpaeus (Molina, 1782) and were
captured in an ecological study performed between 1959
and 1962 in Catán Lil (39°33⬘S, 70°35⬘W), Neuquén Prov-
ince, Argentina, by Crespo and De Carlo (1963). Twenty-
nine specimens did not have a fully erupted dentition,
whereas the remainder was comprised of animals with fully
erupted dentition. Although the absolute age for both
extremes of the age range (from 2 months to 11 years old)
was determined by previous work (see Crespo and De
Carlo 1963; Zapata et al. 1997), it is unknown for most
intermediate stages. As similar studies that used age classes
(e.g., La Croix et al. 2011; Tanner et al. 2010), we deWned
age classes in order to maximize the information for a
period when major critical changes in skull morphology
occur (i.e., the period from 2 months to 1 year old). Age
classes were estimated from dental formulae and tooth
wear, and are deWned as follows:
J1, complete deciduous dentition present and with per-
manent P1 and P1 erupting;
J2, permanent I1, I1, and I2 erupted and with I2, M1, and
M1 erupting;
J3, permanent incisors and canines erupted, with M1
and P2 erupted, and P4, M2, and M2 erupting;
J4, deWnitive incisors, canines, and molars fully
erupted. With P3, P3, P4, and M3 erupting;
A1, complete permanent dentition with no wear;
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Zoomorphology (2012) 131:79–92 81
123
A2, complete permanent dentition with slight wear,
with blunt cusps of incisors, canines, premolars, and
molars.
A3, complete permanent dentition with dentine horns
exposed on the cusps of premolars and molars and I3 at
the same level that I1 and I2.
Additional data are given in online resource 1
Analyses of growth and development
We test for allometric eVect in skulls shape employing geo-
metric morphometric and multivariate allometric tests for
each measurement. Geometric morphometric methods test
the signiWcance of size–shape in the global conWguration of
the skull and multivariate allometry tests it for each mea-
surement, thus allowing the exploration of the signiWcance
of allometry in speciWc skull traits. Also, geometric mor-
phometrics are ideal to capture the shape of structures usu-
ally studied with a qualitative approach (e.g., crest
development), diYcult to quantify using linear measure-
ments and the multivariate allometry approach.
For the multivariate allometry analysis, we used 25 lin-
ear measurements representing length, width, and height of
skull structures in order to detect allometric trends during
skull growth (Table 1; Fig. 1). This approach is based on
the generalized allometry equation proposed by Jolicoeur
(1963a, b). In multivariate allometry, size is regarded as a
latent variable aVecting all measured variables simulta-
neously. The elements of the Wrst eigenvector of a principal
components analysis (PCA) express the allometric relation-
ships of all variables with the latent size. This eigenvector
is extracted from a variance–covariance matrix of log-
transformed variables and scaled to unity. For a given vari-
able, allometry is the statistical deviation of its correspond-
ing eigenvector element from a hypothetical isometric
value that is expected to be equal for all elements if the glo-
bal growth pattern is isometric (size invariant). The isomet-
ric element value is calculated as 1/P0.5 (0.2 for the present
study) with Pvalue equal to the number of variables. Statis-
tical deviation from isometry was estimated using the jack-
knife procedure (Manly 1997; Tukey 1956) developed by
Giannini et al. (2004). The purpose of this technique is to
generate conWdence intervals for each of the empirically
derived Wrst eigenvector elements. The conWdence interval
may be inclusive of the isometric (null) value 0.2 and there-
fore statistically indistinguishable from isometry, or it may
exclude such value and therefore be considered signiW-
cantly allometric: either “positive” if the observed element
is >0.2 or “negative” if the observed element is <0.2. To
calculate this conWdence interval, npseudosamples are gen-
erated such that a new Wrst unit eigenvector is calculated
from a matrix with one specimen of L.culpaeus removed at
a time (with nequal to the number of specimens). In each
cycle, a pseudovalue is calculated for each eigenvector
element using the formula for the Wrst-order jackknife
(see Giannini et al. 2010 for details). The mean of
npseudovalues represents the jackknife estimate of the
multivariate allometry coeYcient for that variable. The
diVerence between this estimate and the actual value from
the complete sample is a measure of bias; we report an
unbiased jackknife estimate of the allometry coeYcient that
results from subtracting the bias from the raw estimate
(Manly 1997). The standard deviation and the correspond-
ing 99% conWdence interval (for n¡1 degrees of freedom)
are calculated for each allometry coeYcient. Giannini et al.
(2004, 2010) and Flores et al. (2006) followed Manly’s
(1997) suggestion of using trimmed pseudovalues for the
calculation of the conWdence interval. Trimming the
mlargest and msmallest pseudovalues for each variable
may signiWcantly decrease the standard deviations and
allow for more realistic allometric estimations. If
untrimmed and trimmed conWdence intervals greatly diVer
in width, this can be taken as indication of extreme pseudo-
values aVecting the standard errors. Here, we report both
untrimmed and trimmed (with m=1) calculations, opting
for the results that in combination reduce bias and interval
width. For the multivariate statistical analysis (PCA + jack-
knife resampling), an R-script (R Development Core Team
2004) from Giannini et al. (2010) was used and is available
from the authors.
For the geometric morphometrics approach, we analyzed
4 views of the skull: dorsal, lateral and ventral cranium, and
lateral mandible. Images of dorsal and ventral view were
captured by orienting specimens with the palate parallel to
the photographic plane. Images of the lateral view were
obtained orienting the specimens with the sagittal plane
parallel to the photographic plane. Images of lateral view of
the mandible were captured orienting the long axis of the
dentary parallel to the photographic plane and at the same
distance from the skull. We identiWed and digitized, from
photographs, for the skull in dorsal view 13 landmarks and
29 semi-landmarks; in ventral view, 15 landmarks and 15
semi-landmarks; in lateral view, 14 landmarks and 19 semi-
landmarks, and for mandible, 7 landmarks and 15 semi-land-
marks (see “Appendix 2”; Fig. 1), which could adequately
describe skull shape. The landmarks used in this study were
deWned as type 1 and type 2, and the semi-landmarks were
deWned as type 3 according to Bookstein (1991). The semi-
landmarks were positioned using MakeFan 6 (Sheets 2002),
which draws fan-shaped lines on photographs, enabling
digitization of semi-landmarks located at the intersection of
the fan lines with the outlines of anatomical structures. In
dorsal view, semi-landmarks were positioned at the inter-
section of the curving of cranial vault and zygomatic arch,
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82 Zoomorphology (2012) 131:79–92
123
using two fans, deWned by the apex of zygomatic arch, and
landmarks 5, 17, and deWned by supraorbital process, and
landmarks 17, 25. In lateral view, were positioned at the
intersection of the curving of cranial vault and muzzle,
using two fans, from apex of postglenoid process, and land-
marks 9, 24, apex of infraorbital process, and landmarks 18,
21, and one grid deWned by landmarks 1 and 4. In ventral
view, were positioned at the intersection of zygomatic arch
and muzzle, using one fan, deWned by apex of zygomatic
arch, and landmarks 8 and 30. In mandible view, were posi-
tioned at the intersection of the curving as evenly spaced
points, from landmark 1 to 10 (Fig. 1). We used tpsUtil
1.40 (Rohlf 2008a, b) to compile image Wles, and both land-
marks and semi-landmarks were digitized onto the images
using tpsDig 2.12 (Rohlf 2008a, b). TpsUtil 1.40 was also
used to deWne “slider-Wles” to distinguish between real
landmarks and semi-landmarks. Landmark conWgurations
were superimposed through generalized procrustes analysis
(GPA Goodall 1991; Rohlf 1999), which minimizes the
sum of squared distances between homologous landmarks
by translating, rotating, reXecting, and scaling them to unit
(the consensus), using tpsRelw 1.35 (Rohlf 2003a, b). The
centroid size, deWned as the square root of the sum of
squared distances of each landmark from the centroid of
the landmark conWguration, was used as estimate of skull
and mandible size (Bookstein 1991; Zelditch et al. 2004).
The procrustes coordinates of landmarks of aligned speci-
mens were obtained with the GPA. For sliding semi-land-
marks, we used the minimum bending energy of the thin
plate spline function (Bookstein 1997). To better describe
shape variation at diVerent scales, we used partial warps
(=PW) and uniform components (=Uni) extracted by the
Table 1 Summary of results of multivariate cranial allometry in L.culpaeus
Abbreviations as in Fig. 1 except MB mastoid breadth, CanB breadth at canines
The Wrst three data columns show results using all specimens. The remainder of the columns shows jackknife results calculated with untrimmed and (m_1)
trimmed sets of pseudovalues (see “Materials and methods”). Allometry coeYcient is the correspondent element of the Wrst (unit) eigenvector per variable.
The expected coeYcient (0.2) is the value under isometry (equal for all variabl es). The observed coeYcient is the value obtained with all specimens included
(n= 101). The resampled coeYcient is the Wrst-order jackknife value. Bias is the diVerence between the resampled and observed coeYcients. The jackknife
99% conWdence interval is provided; allometric variables are those whose conWdence interval excludes the expected value under isometry (0.2). Growth
trend is the summary allometry of each variable presented in symbols: = isometry, ¡ negative allometry, + positive allometry
Variable Expected
allometry
coeYcient
Observed
allometry
coeYcient
Observed
departure
Untrimmed values Trimmed values
Resampled
allometry
coeYcient
Bias 99% CI Growth
trend
Resampled
allometry
coeYcient
Bias 99% CI Growth
trend
CBL 0.2 0.1872 ¡0.0128 0.1872 ¡0.0008 0.1767–0.1976 ¡0.1850 0.0003 0.1764–0.1936 ¡
HO 0.2 0.1159 ¡0.0841 0.1159 ¡0.0001 0.0954–0.1364 ¡0.1161 ¡0.0001 0.0985–0.1337 ¡
MB 0.2 0.1105 ¡0.0895 0.1105 ¡0.0003 0.0942–0.1268 ¡0.1109 ¡0.0005 0.0958–0.1259 ¡
BB 0.2 0.0462 ¡0.1538 0.0462 ¡0.0001 0.0224–0.0699 ¡0.0511 ¡0.0026 0.0349–0.0672 ¡
BZ 0.2 0.2613 0.0613 0.2613 ¡0.0002 0.2343–0.2882 + 0.2677 ¡0.0034 0.2444–0.291 +
LO 0.2 0.1094 ¡0.0906 0.1094 0.0000 0.0825–0.1362 ¡0.1115 ¡0.0011 0.0879–0.135 ¡
LN 0.2 0.2365 0.0365 0.2365 ¡0.0007 0.2130–0.2600 + 0.2376 ¡0.0012 0.2159–0.2592 +
LR 0.2 0.2101 0.0101 0.2101 ¡0.0012 0.1779–0.2423 = 0.2061 0.0008 0.1786–0.2336 =
CanB 0.2 0.1338 ¡0.0662 0.1338 ¡0.0003 0.0973–0.1704 ¡0.1442 ¡0.0054 0.1156–0.1727 ¡
HM 0.2 0.1763 ¡0.0237 0.1763 0.0004 0.1306–0.2220 = 0.1799 ¡0.0014 0.1405–0.2193 =
BBu 0.2 0.0528 ¡0.1472 0.0528 0.0006 0.0096–0.0960 ¡0.0539 0.0000 0.0152–0.0927 ¡
HBu 0.2 0.0078 ¡0.1922 0.0078 ¡0.0001 ¡0.0456–0.0612 ¡0.0158 ¡0.0041 ¡0.0316–0.0633 ¡
LBu 0.2 0.0124 ¡0.1876 0.0124 ¡0.0002 ¡0.0414–0.0662 ¡0.0133 ¡0.0007 ¡0.0335–0.0602 ¡
BP 0.2 0.0555 ¡0.1445 0.0555 0.0003 0.0229–0.0881 ¡0.0597 ¡0.0019 0.0311–0.0884 ¡
LP 0.2 0.1800 ¡0.0200 0.1800 ¡0.0006 0.1667–0.1934 ¡0.1792 ¡0.0002 0.1668–0.1916 ¡
Upr 0.2 0.2813 0.0813 0.2813 ¡0.0037 0.1977–0.3649 = 0.2653 0.0043 0.1881–0.3426 =
LD 0.2 0.2041 0.0041 0.2041 ¡0.0008 0.1942–0.2139 = 0.2028 ¡0.0001 0.1941–0.2115 =
HMb 0.2 0.2251 0.0251 0.2251 0.0011 0.1640–0.2863 = 0.2306 ¡0.0016 0.1772–0.284 =
HMr 0.2 0.2612 0.0612 0.2612 ¡0.0010 0.2427–0.2796 + 0.2599 ¡0.0003 0.2431–0.2766 +
LC 0.2 0.3132 0.1132 0.3132 0.0002 0.2536–0.3727 + 0.3251 ¡0.0058 0.2763–0.3739 +
Lpr 0.2 0.3353 0.1353 0.3353 ¡0.0039 0.2383–0.4324 + 0.3212 0.0031 0.2300–0.4125 +
Ilm 0.2 0.2382 0.0382 0.2382 0.0002 0.1920–0.2845 = 0.2401 ¡0.0007 0.1982–0.282 =
Ilt 0.2 0.3124 0.1124 0.3124 ¡0.0005 0.2831–0.3416 + 0.3125 ¡0.0006 0.2866–0.3384 +
Jcar 0.2 0.1655 ¡0.0345 0.1655 0.0003 0.1288–0.2023 = 0.1700 ¡0.0019 0.1358–0.2043 =
Jcan 0.2 0.2253 0.0253 0.2253 ¡0.0007 0.2131–0.2374 + 0.2249 ¡0.0005 0.2137–0.2361 +
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Zoomorphology (2012) 131:79–92 83
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bending energy matrix of the thin plate spline function. An
allometric analysis was performed by regressing the par-
tial warps (and the uniform components) of the complete
pooled sample, calculated from the coordinates obtained
from the GPA, on the centroid size (with the tpsRegr 1.28
software; Rohlf 2003a, b). The change of shape along the
size (centroid size) gradient was illustrated through defor-
mation grids obtained with tpsRegr 1.28. The signiWcance
of the regression was tested with the Generalized Goodall
Ftest, the Wilks’ Lambda, and a permutation test with
1,000 resamples. Procrustes distance between each speci-
men and the consensus of the youngest category was used
as an index of shape change (see Tanner et al. 2010) and
was calculated as the square root of the summation of the
distance between each landmark of 1 specimen and this
mean. These estimations were calculated with the soft-
ware R 2.9.2 (R Development Core Team 2004). DiVer-
ences in size, shape (procrustes distance), and mechanical
advantage of masseter and temporal muscles between suc-
cessive age classes were tested with the Mann–Whitney
Utest (Zar 1984).
Previous authors showed that L.culpaeus presents some
sexual dimorphism in adult external and cranial measure-
ments (Crespo and De Carlo 1963; Johnson and Franklin
1994; Travaini et al. 2000). In this sense, we tested the
presence of sexual dimorphism in size (centroid size) and
shape (landmark coordinates of aligned specimens obtained
in the GPA) using the Mann–Whitney Utest (Zar 1984)
and the nonparametric MANOVA (Anderson 2001),
respectively. These analyses were performed with the soft-
ware PAST 1.98 (Hammer et al. 2001). The distribution of
females, males, and unsexed specimens in the age classes
was: J1: 2/3/2; J2: 2/1/0, J3: 1/2/2; J4: 5/5/4, A1: 13/13/4;
A2: 13/13/0; A3: 3/4/9. Unfortunately, for most of the juve-
nile classes, the proportion of sexed specimens was very
low. Due to this, and to the general absence of signiWcant
sexual dimorphism in size and shape (only shape of the
skull in lateral view of class A1, centroid size of all views
of class A2, centroid size of mandible, ventral and lateral
skull views of class A3 were signiWcant with P·0.05), we
pooled the sexes together in each age class. The allometric
analyses of male and female subsamples gave the same pat-
tern of ontogenetic variation, in relation to each other and
to the whole sample analysis (data not showed). They indi-
cate that the observed allometric pattern is not biased by the
sexual dimorphism present in size; thus, we were conWdent
to pool the whole sample.
Mechanical advantage
We calculated the mechanical advantage and size of the
temporalis and masseter masticatory muscles in order to
infer relative bite force, following Radinsky (1981) and
Fig. 1 Cranial landmarks (large dots), semi-landmarks (small dots),
and measurements of Lycalopex culpaeus for dorsal (a), ventral (b),
lateral (c), and mandible (d)views. BB breadth of braincase, BBu
breadth of auditory bulla, BP breadth of palate, BZ interzygomatic
breadth, CBL condylobasal length, HBu height of auditory bulla, HM
height of muzzle, HMb height of mandibular body, HMr height of
mandibular ramus, HO height of occipital plate, Ilm in-lever of the
masseter, Ilt in-lever of the temporalis, Jcan out-lever to canine
point, Jcar out-lever to carnassial point, LBu length of auditory bulla,
LC length of coronoid process, LD length of mandible, LN length of
nasals, LO length of orbit, LP length of palate, Lpr length of lower
postcanine row, LR length of rostrum, Upr length of upper postca-
nine row
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84 Zoomorphology (2012) 131:79–92
123
Tanner et al. (2010). Mechanical advantage was estimated
as the in-lever of each muscle divided by out-lever for each
muscle. The in-lever of the temporalis was measured as the
distance from the dorsal tip of the coronoid process to the
mandibular condyle (Ilt) and the in-lever of the masseter as
the distance from the mandibular condyle to the middle of
the masseteric fossa (Ilm). Out-levers for both muscles
were measured as the distance from the mandibular condyle
to the bite point (in this work, to the carnassial notch, Jcar,
and to the center of the crown of lower canine, Jcan). Mas-
ticatory muscle size was also estimated as the maximum
width across the zygomatic arches BZ (Fig. 1).
Results
Multivariate allometry
The Wrst principal component accounts for 70.8% of the
total variance. Observed multivariate coeYcients of allom-
etry varied widely across variables (Table 1; Fig. 1). Aver-
age estimated bias (using absolute jackknife values) across
coeYcients calculated from trimmed and untrimmed values
were both small (0.0007 and 0.0017, respectively). Trend
obtained with untrimmed and trimmed values did not diVer
in any of the variables, that is, extreme pseudovalues did
not aVect jackknife estimates. Two variables showed the
smallest observed departure from isometry: length of the
mandible (LD) and length of the rostrum (LR), (0.0041 and
0.0101, respectively, Table 1), which could be considered
as independent variables in further bivariate analyses of
allometry. Height of the bulla exhibited the largest depar-
ture from isometry (¡0.1922). Eighteen variables signiW-
cantly departed from isometry, 11 of them were negatively
allometric mostly related with the neurocranium: breadth of
braincase (BB), length of orbit (LO), height of occipital
plate (HO), intermastoid breadth (MB), height of auditory
bulla (HBu), length of auditory bulla (LBu), breadth of
auditory bulla (BBu), breadth of palate (BP), length of pal-
ate (LP), condylobasal length (CBL), and intercanine
breadth (CanB). Seven of them were positively allometric
and related with the splachnocranium: jaw joint to canines
(Jcan), height of mandibular ramus (HMr), length of coro-
noid process (LC), length of lower postcanine row (Lpr),
in-lever of temporalis muscle (Ilt), zygomatic breadth (BZ),
and length of nasals (LN).
Geometric morphometrics
In the analysis of dorsal view, size explained 5.2727% of
the shape, a relationship that was highly signiWcant
(F= 5.4096, P< 0.0001, Wilks’ Lambda = 0.1778). Juvenile
specimens showed a relatively smaller temporal fossa, a
thinner zygomatic arch, a wider postorbital constriction, a
supraorbital process with smoother outline, a rounder brain-
case and a wider and shorter muzzle (Fig. 2a). Adult speci-
mens were characterized by relatively elongated nasals, a
larger temporal fossa, more developed zygomatic arches, a
narrower postorbital constriction and braincase (Fig. 2a).
In the analysis of the ventral view, size signiWcantly
explained 7.9055% of shape (F= 8.2500, P< 0.0001,
Wilks’ Lambda = 0.1585). Juvenile skulls were associated
with a relatively narrower zygomatic arch and shorter
broader muzzle (Fig. 2b). Adult skulls were associated with
relatively stronger, wider zygomatic arches, wider temporal
fossae, relatively closed glenoid fossae, and shorter pala-
tines (Fig. 2b).
In the analysis of the lateral view of the skull, size
explained 3.3765% of the shape (F= 3.3978, P< 0.0001,
Wilks’ Lambda = 0.1375). Juvenile skulls had a relatively
rounded braincase, short rostrum, and the zygomatic arch
and orbit in a lower and more lateral position (Fig. 2c).
Adult skulls were associated with a relative growth of the
infraorbital process, change of position in the orbit from
lateral to latero-dorsal, Xattening of the braincase and
occipital plate, strengthening of the zygomatic arch and its
shift to a more latero-dorsal position, lengthening of the
upper postcanine row, and muzzle elongation (Fig. 2c).
In the mandible analysis, size explained 5.8779% of the
shape variation (F= 6.1871, P< 0.0001, Wilks’ Lambda =
0.1757). Juvenile skulls were associated with a relatively
thinner and more curved mandibular corpus, and a thinner
mandibular ramus more posteriorly placed (Fig. 2d). Adult
skulls were associated with a relatively more elongated
masseteric fossa, more developed angular process, greater
separation between condyloid and angular processes,
straighter mandibular body, a more vertical coronoid pro-
cess and thicker mandibular ramus (Fig. 2d).
Changes in size, shape, and mechanical advantages
throughout ontogeny
Median skull size, measured as centroid size of each view
of the crania and mandible (Figs. 3a, b), showed rapid and
sustained growth from age class J1 to J2/J3 when the adult
size is reached. We only found signiWcant diVerences
between classes J1–J2 with the Mann–Whitney Utest (See
Table 2).
The median shape change index of dorsal (Fig. 3c) and
ventral views showed similar values for juvenile classes,
then increased beginning in class A1, and next decreased in
the last class A3 in the ventral view. Lateral skull and man-
dible (Fig. 3d) views showed a sustained growth from J1 to
J4 and then shape reached an asymptote from J4 to A3.
These tendencies were based on median values for each
category, but there was a large amount of variation that
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Fig. 2 Allometric change of the skull and biplots of centroid size (CS) versus procrustes distance (PD) of Lycalopex culpaeus, for dorsal (a),
ventral (b), lateral (c), and mandible (d) views. For each view, the lower size extreme (light color) and upper extreme of size (dark color)
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became evident in the overlap of the ranges as well as in the
25 and 75% quartiles (Figs. 3c, d). Mann–Whitney Utest
only detected signiWcant diVerences between classes J4–A1
and A1–A2 in dorsal (See Table 2).
There were clear patterns of ontogenetic change in the
mechanical advantage of the masseter and temporalis mus-
cles. Median BZ showed a sharp increase from class J1 to
A2–A3 (Fig. 3e). The mechanical advantage of the masse-
ter muscle measured at the canine showed a pattern of
slight decrease with higher values for class J1 decreasing
toward J4, but these diVerences were small and the trend
was not very clear. Median mechanical advantage of the
masseter measured at the carnassial showed a slight
increase until class A1 when it reached adult values. The
median mechanical advantage of the temporal muscle mea-
sured at the canine and carnassial showed a sustained
increase from J2 to A2 and a slight decline in value for
class A3 (Fig. 3f). The J2 class possessed the lowest
median in some of these measurements. The only signiW-
cant diVerences detected by the Mann–Whitney Utest were
the BZ (See Table 2). Additional data are given in online
resource 2, 3, and 4.
Discussion
Postnatal skull ontogeny in Lycalopex culpaeus
Morphologic and morphometric transformations and inter-
actions between the neurocranium and splachnocranium
have profound impacts on the strength and function of the
adult skull. The detected changes encompassed the relative
enlargement of the temporal fossa (related with positive
allometry of zygomatic breadth, BZ, and negative allometry
of braincase, BB) and a relative decrease in size of the post-
orbital constriction, occipital plate (HO and MB), and the
braincase (BB). Sensory capsules such as auditory bulla
(BBu, HBu, and LBu) and LO, also scaled negatively fol-
lowing the general pattern of most vertebrates (e.g., Emer-
son and Bramble 1993; Table 1). The splanchnocranium
underwent growth and strengthening that aVected the BZ,
deepening of the masseteric fossa, and reaching a vertical
orientation of the coronoid process (Fig. 2). The observed
positive allometry of most mandibular variables and the in-
lever of temporalis (Ilt, Table 1) is related to an increase in
bite force and stress support during prey apprehension as
acquired in other carnivorans (Slater et al. 2009; Tseng
2009; Tseng and Wang 2010; see below). The palate being
relatively longer and wider in young L.culpaeus, developed
by the negative allometry in its length (LP), breadth (BP),
and intercanine breadth (CanB, Table 1). These features are
associated with a functional condition of the palate in
young, which acts as a platform of the tongue during suck-
ling, as observed in some marsupial carnivores (e.g., Didel-
phis albiventris Lund, 1840, Abdala et al. 2001; Dasyurus
albopunctatus Schlegel, 1880, Flores et al. 2006). On the
other hand, the rostrum of L.culpaeus showed a diVerent
pattern with positive allometry in nasals (LN) and isometry
in upper postcanine row (Upr, Table 1). Such complexity of
the splanchnocranium can also be detected in diVerent allo-
metric trends obtained for both postcanine rows, isometric
in the upper (Upr), and positively allometric in the lower
one (Lpr), while both postcanine rows are of the same length
in adults. This can be related with the dental eruption
sequence in L.culpaeus. Normally, the upper postcanine
row has 1 more tooth than the lower row at a given time,
until the Wnal tooth count is attained in adults (see age clas-
ses description). Therefore, this diVerence is compensated
by a faster rate of growth to maintain the same length in the
upper and lower tooth row. The lower tooth row, having
started with fewer teeth, grows faster to reach its Wnal
length. An inverse pattern of growth was detected in some
didelphids (Abdala et al. 2001, Flores et al. 2003).
Fig. 3 Boxplots of skull centroid size versus age classes of Lycalopex
culpaeus, for dorsal (a) and mandible (b)views. Boxplots of skull pro-
crustes distance of each specimen of all age classes to the mean of J1
class, for dorsal (c) and mandible (d)views. Boxplots of mechanical
advantage (MA) versus age classes of zygomatic breadth (e)and
mechanical advantage of temporal muscle measure at the carnassial (f).
The boxplots include median, upper, and lower quartiles (75 and 25%,
respectively), minimum and maximum. In aand b, horizontal lines
indicate the oVset of development in shape and in cand dgrowth in
size
Table 2 Summary of results of Mann–Whitney Utest for cranial
allometry in L.culpaeus
Un1n2P
J1–J2 dorsal view 0 7 3 <0.0170
J1–J2 ventral view 0 7 3 <0.0170
J1–J2 lateral view 0 7 3 <0.0170
J1–J2 mandible view 1 8 3 <0.0250
J2–J3 mandible view 0 3 5 <0.0260
J3–J4 lateral view 7 5 14 <0.0096
J3–J4 mandible view 7 5 14 <0.0096
J4–A1 dorsal view 90 23 21 <0.0004
J4–A1 ventral view 57 14 30 <0.0002
A1–A2 dorsal view 97 21 26 <0.0002
A1–A2 ventral view 89 30 25 <0.0001
Zygomatic breadth 57 14 31 <0.0001
Temporal mechanical
advantages J4–A1 at canine
110 14 31 <0.0090
Temporal mechanical
advantages J4–A1 at carnassial
133 14 31 <0.0400
Temporal mechanical
advantages A1–A2 at canine
76.5 31 23 <0.0001
䉳
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In relation to the cranial shape change along the ontoge-
netic sequence (Figs. 3c, d), we observed that the dorsal
and ventral views reach the adult shape at class A2. This
class includes specimens being more than 1 year old and
sexually mature (Novaro 1997). The lateral and mandibular
views reached adult shape earlier, at the J4 age class,
including young specimens with not yet fully erupted per-
manent dentition, but with adult size. This is in agreement
with Crespo and De Carlo (1963), who reported that juve-
niles at 7 months of age are similar to adults in general
appearance and body size (about 10 kg). This was also con-
Wrmed by the plot of centroid size by age categories
(Fig. 3a, b) where the size of each cranial and mandible
views reached adult Wgures in J4 class, although also we
detected large variation in the sample of this class. In any
case, it must be noted that the median of the earlier classes
(i.e., J3 or even J2) had similar values to the older ones,
indicating that size changes happened earlier, before reach-
ing adult shape, which happens between J4 and A2.
Zygomatic arch breadth, which reXects the size of jaw
musculature, is allometrically positive (Table 1), increased
rapidly, and showed stable values in age class A2, but with
slight decrease in A3 (Fig. 3e). This might be the result of
bone resorption and muscle weakness that occurs in very
old specimens (>10 years old; Jiménez and Novaro 2004).
The abrupt progression of this measure is followed by other
estimators of mechanical advantage. In some cases,
mechanical advantage of the temporalis at the carnassial
and at the canine increases through ontogeny, except when
going from J1 to J2. This fact might have been an error gen-
erated by the low sample size and the large variation repre-
sented by this class (Fig. 3f). The mechanical advantage of
the temporalis at the carnassial increased more progres-
sively than those measured at the canine, while in the case
of the masseteric, the increase in mechanical advantage at
the carnassial was less marked (Fig. 3f). Values of the mas-
seteric mechanical advantage were highly variable through-
out ontogeny, although similar to the advantage at the
carnassial and the canine, with a slight decrease in the latter
and a stronger advantage at the carnassial, as observed in
the A1 to A3 classes. The detected pattern of change in the
mechanical advantages was similar to the observed in shape
changes (Fig. 3c–f), but contrasting with the changes in
centroid size along the ontogeny of L.culpaeus (Fig. 3a, b).
Ontogeny and feeding performance
These ontogenetic changes paralleled the acquisition of an
omnivorous diet (although includes insects and vegetables,
also includes hunting and processing of vertebrates preys)
and aVected mainly the trophic apparatus, the occiput and,
presumably, their linked functions (feeding and head move-
ments). Such characters are linked with larger volume of
the masticatory muscles and their insertion areas, as well as
with the amount of mechanical resistance of the food and
preys. The interaction of morphologic and morphometric
changes of the neurocranium and trophic apparatus
described herein was expected, because growth pattern in
L.culpaeus coincides with changes in feeding habits (from
lactation to omnivorous diet) and the learning of hunting
and killing prey methods required for an independent exis-
tence as a predator (Binder and Van Valkenburgh 2000;
Ewer 1973). Shape changes (Fig. 2) and allometric growth
trends (Table 1) are clearly related to functional improve-
ments in terms of jaw mechanics, prey capture, and food
ingestion and processing, as most of the deWnitive jaw mus-
cle size and advantage, as well as the adult cranial shape
(except for the mandible and lateral view of the skull) are
reached after sexual maturity (around 1 year) at age cate-
gory A2. The age of maturity is probably related to the time
of independence and dispersion of individuals (Ewer 1973)
when a more eYcient skull and mandibular complex are
needed to hunt and process prey. The delay between sexual
maturity and the attainment of adult cranial morphology
indicates that L.culpaeus have an “adjustment” period
when they do not yet possess full adult levels of feeding
performance, as observed in other species (e.g., Tanner
et al. 2010; see below). In contrast, adult mandible and
skull size are reached after weaning (t2 months, see Cre-
spo and De Carlo 1963; Novaro 1997), in class J2, just
when the diet changes by the incorporation of meat and
other food items occur.
Comparison with other species of the Carnivora
Both limited information and lack of knowledge about cra-
nial ontogeny in other terrestrial carnivores restricted the
comparison of the cranial ontogenetic pattern described for
L.culpaeus. However, some information about allometric
trends based on skull measurements and qualitative
description is available for domestic dogs, C.familiaris and
cougars, Puma concolor (Linnaeus, 1771) (Evans 1993;
Gay and Best 1996; Giannini et al. 2010; Segura and Flores
2009; Wayne 1986), and geometric morphometric analyses
have been recently conducted for the spotted hyaena, Cro-
cuta crocuta (Erxleben, 1777) (Tanner et al. 2010), coy-
otes, C.latrans (La Croix et al. 2011) and for dogs,
C.familiaris and wolves, C.lupus (Drake 2011).
Compared with C.familiaris, L.culpaeus does not share
the same scaling pattern in skull length (here negatively
allometric) but shares the allometric scaling pattern of skull
width and depth, which results in dramatic changes in the
relative skull width of puppies as they grow (Wayne 1986).
However, the results of Wayne (1986) were based on a
mesaticephalic dog breed (German shepherds, with average
skull), whereas nothing is known about the ontogenetic
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arrangement in morphologically extreme breeds (dolioce-
phalic and brachycephalic). Puppies with short and wide
skulls as observed in L.culpaeus (Fig. 2) seem to be a gen-
eralized characteristic in canids, because it is a pattern also
detected in C.familiaris (Wayne, 1986), C.latrans (La
Croix et al. 2011), and C.lupus (Drake 2011). Additionally,
some C.familiaris breeds (adult specimens) exhibit a char-
acteristic rearrangement of the skull in which the palate and
basicranium rotate each other (Drake 2011). L.culpaeus
does not share these adjustments with these dogs but
C.lupus, in which palate and basicranium remain in the
same plane throughout development. Other canids such as
C.latrans present a similar pattern in the growth of its sag-
ittal and occipital crests, angular and coronoid processes,
and narrowing of the braincase, but not in strong elongation
of the rostrum and narrowing of the zygomatic arches (La
Croix et al. 2011). These diVerences could be partly due to
the lack of very young specimens in our sample (i.e., neo-
nates and pre-weaning) that have extremely short rostrum.
C.latrans reach their adult mandible and skull size before
sexual maturation, as in L.culpaeus (La Croix et al. 2011),
but its adult skull shape is attained even earlier than adult
size, and only the adult shape of the mandible is reached
after adult size. This is a sharp diVerence with L.culpaeus,
in which the Wnal adult skull shape in ventral and dorsal
views is reached after sexual maturation.
Although L.culpaeus and the felid P.concolor probably
show greater ontogenetic diVerences in the orbitotemporal
and mandible regions in strictly morphological terms (see
Segura and Flores 2009), both species exhibited a similar
pattern of allometric growth, with negative trends in sen-
sory capsules (orbit, tympanic bulla, and breadth of brain-
case among others) and positive allometry variables related
with the trophic apparatus such as zygomatic breadth,
height of mandibular ramus, length of coronoid process,
suggesting that the sensory capsules grow at a slower pace
than the splachnocranium (see Giannini et al. 2010). Nega-
tive allometry of the braincase and sensory capsules
through ontogeny is a general pattern that has also been
observed in other carnivorous or omnivorous metatherian
mammals such as D.albopunctatus, Lutreolina crassicau-
data (Desmarest, 1804), D.albiventris, and Caluromys phi-
lander (Linnaeus, 1758) (Abdala et al. 2001; Flores et al.
2003, 2006, 2010) and could be linked to the retention of a
plesiomorphic feature. Indeed, negative allometry of some
sensory capsules (e.g., orbits) was detected in static inter-
speciWc allometric studies (Finarelli and Goswami 2009;
Noble et al. 2000; Ravosa et al. 2000) made only on adult
specimens, which was related to encephalization and orbit
orientation.
The ontogenetic change observed in C.crocuta also
showed the same tendency of strengthening of the skull
associated with weaning and shifting to a carnivorous diet,
as observed in P.concolor (Giannini et al. 2010; Segura
and Flores 2009) and L.culpaeus (this report). However,
although the skulls of the juveniles of both species were
similar in shape, adult hyenas had more remarkable mor-
phological change than adult L.culpaeus (see Tanner et al.
2010, Figs. 4, 5, 6, 7), probably related to a more special-
ized diet and bone processing (Biknevicius and Leigh 1997;
Binder and Van Valkenburgh 2000). An additional diVer-
ence is that in L.culpaeus, adult skull size was reached
before sexual maturity, but adult shape for most cranial
views and muscle advantage (bite forces) values were
reached after this age, with the exception of the lateral view
of the skull and the mandible, which attain adult conWgura-
tions in subadult age (class J4, around 7 months). In con-
trast, adult skull size in Crocuta was reached soon after
reproductive maturity and adult shape, a year after that
(Tanner et al. 2010).
Conclusion
In summary, the ontogenetic pattern observed in
L.culpaeus was similar to that of its close relatives,
C. familiaris and C.latrans (Wayne 1986; La Croix
et al. 2011), but presented less morphological changes
compared to that of the hyaenid C. crocuta (Tanner et al.
2010). The felid P. concolor possessed an intermediate
pattern, with strong changes (see Tables 1 and 2 in
Segura and Flores 2009), and more profound shape
changes than those of the L.culpaeus, but less than those
observed in Crocuta (see Fig. 1 in Tanner et al. 2010).
Such diverse patterns are linked to dietary habits and
specialization that impact skull anatomy (Van Valken-
burgh 1989, 2007), because both the L.culpaeus and the
domestic dog are generalized species (Novaro 1997),
while P.concolor and C.crocuta are hypercarnivores
(Holekamp and Kolowski 2009), the latter also being
ossiphagous (Tseng and Binder 2010). If this hypothesis
is correct, we would expect more changes (e.g., more
development of nuchal and sagittal crests, strengthening
of zygomatic arch and mandible, and decreasing of
breadth of braincase) in postnatal skull morphology in
more specialized taxa. On the other hand, P. concolor
and Crocuta have a more recent common ancestor in
comparison with the other studied carnivores, while the
canids belong to the same clade (Canidae); thus, it is
possible that the pattern of similarities/diVerences
observed between the skull ontogeny of these carnivores
could be explained by phylogenetical relatedness. More
carnivorous species must be analyzed to test these
hypotheses and to evaluate the potential presence of a
phylogenetic pattern in the cranial ontogeny of these
carnivores.
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90 Zoomorphology (2012) 131:79–92
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Acknowledgments We thank David Flores for the permission to
study the material under his care; to Pablo Teta for his drawings of
L.culpaeus skulls; to Erika Hingst-Zaher, Amelia Chemisquy, and
David Flores for their critical revision of the preliminary version of this
manuscript and to Cecilia Morgan for her revision of English grammar.
We also thank to three anonymous reviewers who provided many help-
ful suggestions to this study. This research was partially supported by
CONICET (PIP 01054) and ANPCyT (PICT 2008-1798).
Appendix 1
Specimens of Lycalopex culpaeus of Museo Argentino de
Ciencias Naturales Bernardino Rivadavia (MACN) used in
this study
15022; 15024; 15025; 15028; 15033; 15037; 15040;
15044; 15045; 15049; 15050;15055; 15062; 15063; 15064;
15073; 15078; 15081; 15082; 15083; 15089; 15093; 15096;
15101; 15106; 15112; 15119; 15121; 15122; 15123; 15124;
15127; 15129; 15130; 15131; 15132; 15133; 15138; 15140;
15149; 15151; 15154; 15158; 15163; 15168; 15172; 15173;
15177; 15180; 15181; 15182; 15190; 15194; 15196; 15197;
15199; 15200; 15201; 15202; 15203; 15208; 15212; 15220;
15223; 15224; 15226; 15227; 15228; 15229; 15232; 15233;
15240; 15243; 15246; 15248; 15258; 15259; 15260; 15261;
15266; 15267; 15268; 23072; 23076; 23077; 23093; 23095;
23098; 23099; 23100; 23101; 23102; 23103; 23104; 23108;
23119; 23123; 23125; 23143; 23148; 23152.
Appendix 2
DeWnition of the landmarks and semi-landmarks used in the
geometric morphometric analyses (see Fig. 1)
Dorsal landmarks: 1, tip of premaxilla in the sutura inter-
incisiva; 2, anterior portion of the nasals in the sutura inter-
nasalis; 3, midline of sutura frontonasalis; 4, intersection
between sutura coronalis, sutura sagittalis, and sutura inter-
frontalis; 5, tip of occipital plate; 6–16, semi-landmarks;
17, tip of the supraorbital process; 18–24, semi-landmarks;
25, lacrimal foramen; 26–31, semi-landmarks; 32, tip of the
infraorbital process; 33–37, semi-landmarks; 38, apex of
canine root; 39, nasal process; 40, anterior contact of sutura
nasomaxillaris; 41, posterior contact of sutura nasomaxil-
laris; 42, apex of sutura frontomaxillaris.
Ventral landmarks: 1, anterior tip of premaxilla; 2, mid-
line in Sutura incisivomaxillaris; 3, midline in Sutura pal-
atomaxillaris; 4, posterior point of palatine torus; 5, anterior
point of intercondyloid incisure; 6, internal apex of occipi-
tal condyle; 7, apex of jugular process. 8, tip of mastoid
process; 9, internal apex of tympanic bulla; 10, anterior
apex of tympanic bulla; 11–14, semi-landmarks; 15, tip of
postglenoid process; 16, internal edge of masseteric fossa;
17, caudal apex of border of palatine; 18, external edge of
masseteric fossa; 19, anterior edge of masseteric fossa; 20–
30, semi-landmarks.
Lateral landmarks: 1, tip of premaxilla; 2–3, semi-land-
marks; 4, apex of sutura frontomaxillaris; 5–8, semi-land-
marks; 9, posterior point between sagittal and nuchal crests;
10, apex of occipital condyle; 11, tip of paracondylar process;
12, point between nuchal crest and mastoid process; 13, apex
of tympanic bulla; 14–17, semi-landmarks; 18, tip of infraor-
bital process; 19–20, semi-landmarks; 21, lacrimal foramen;
22–23, semi-landmarks; 24, tip of the supraorbital process;
25, tip of Postglenoid process; 26, posterior point of ptery-
goid; 27–29, semi-landmarks; 30, posterior tip of dentary row;
31, notch of carnassial; and 32–33, semi-landmarks.
Mandibular landmarks: 1, anterior tip of body of mandi-
ble; 2–9, semi-landmarks; 10, posterior tip of coronoid pro-
cess; 11, mandibular notch; 12, anterior point of masseteric
fossa; 13, external point of condyloid process; 14, separa-
tion between condyloid and angular process; 15, tip of
angular process; 16–22, semi-landmarks.
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