Osteology and Cranial Musculature of Caiman latirostris
(Crocodylia: Alligatoridae)

Paula Bona1,2* and Julia Brenda Desojo2,3

1División Paleontologı́a Vertebrados, Facultad de Ciencias Naturales y Museo, Paseo del Bosque s/n, 1900, La Plata,
Buenos Aires, Argentina
2CONICET, Consejo Nacional de Investigaciones Cientı́ficas y Técnicas, Argentina
3Sección Paleontologı́a de Vertebrados, Museo Argentino de Ciencias Naturales ‘‘Bernardino Rivadavia,’’ Av. Angel
Gallardo 470 C1405DRJ, Capital Federal, Argentina

ABSTRACT Caiman latirostris Daudin is one of the
extant species of Caimaninae alligatorids characterized
taxonomically only by external morphological features.
In the present contribution, we describe the cranial oste-
ology and myology of this species and its morphological
variation. Several skull dissections and comparisons
with other caimans were made. Although jaw muscles of
living crocodiles show the same general ‘‘Bauplan’’ and
alligatorids seem to have a similar cranial musculature
pattern, we describe some morphological variations (e.g.,
in C. latirostris the superficial portion of the M. adduc-
tor mandibulae externus did not reach the postorbital;
the M. adductor mandibulae internus pars pterygoideus
dorsalis did not reach the pterygoid and lacrimal and
contrary to the case of C. crocodilus the M. adductor
mandibulae internus pars pterygoideus ventralis
attaches to the posterodorsal surface of the pterygoid
and the pterygoid aponeurosis, without contacting the
dorsal and ventral surface of the pterygoid margin; the
M. intermandibularis is attached to the anterior half of
the splenial and posteriorly inserts medially by a medial
raphe that serves as attachment zone for M. constrictor
colli, and the M. constrictor colli profundus presents a
medial notch in its anterior margin). In addition, the
skull of C. latirostris differs from that of other caimans
and possesses several characters that are potential diag-
nostic features of this species (e.g., outline of glenoid
cavity in dorsal view, extension of the rostral ridges, and
occlusion of the first dentary tooth). Nevertheless, these
characters should be analyzed within the phylogenetic
context of the Caimaninae to evaluate its evolutionary
implications for the history of the group. J. Morphol.
000:000–000, 2011. � 2011 Wiley-Liss, Inc.

KEY WORDS: Crocodylia; Alligatoridae; Caimaninae;
Caiman latirostris; cranial osteology; cranial myology

INTRODUCTION

Crocodiles and birds represent the two extant
archosaurian groups and their cranial anatomy
has attracted the interest of many researchers
since the 19th century (Iordansky, 1973).
Although many studies describe the cranial mor-
phology of extant alligatorids (e.g., Brochu 1999;
Rowe et al., 1999) or caimans [e.g., C. crocodylus
(Daudin); Iordansky, 1973; Schumacher, 1973;

Van Drongelen and Dullemeijer, 1982; Cleuren
and De Vree, 2000], our knowledge of the mor-
phological variation among different living spe-
cies is limited (Carvalho, 1951; Diefenbach,
1979), and several of these taxa are not properly
defined by osteological features. The taxonomic
diversity of the fossil record of alligatorids is
wider than the extant, and fossil species are
defined by cranial and jaw osteological charac-
ters. In contrast, living taxa are currently
defined by external morphological characters.
This makes it difficult to understand the evolu-
tionary history of the crown group ‘‘Caiman’’
(sensu Brochu, 1999). The genus Caiman Spix
currently contains three extant species, C. latir-
ostris (Daudin), C. crocodylus, and C. yacare
(Daudin) but the taxon might be paraphyletic
(Fig. 1; Norell, 1988; Brochu, 1999, 2003).
Although the cranial musculature, in particular
the jaw muscles, has been analyzed in C. croco-
dylus (Schumacher, 1973; Van Drongelen and
Dullemeijer, 1982), the musculature of the other
South American species, as well as the morpho-
logical variability of the cranial musculature and
its attachment sites on the skeleton are poorly
known. This study aims to analyze the cranial
morphology of the most extreme broad-snouted
form among the Caiman species, C. latirostris, to
describe the cranial osteology and myology of
this species and its osteological cranial variation.
Complementarily, a quantitative comparison
between C. latirostris and C. yacare is provided.

*Correspondence to: Paula Bona, Departamento de Paleontologı́a
Vertebrados, Museo de La Plata, Paseo del Bosque s/n, 1900, Argen-
tina. E-mail: pbona@fcnym.unlp.edu.ar

Received 10 November 2009; Revised 29 May 2010;
Accepted 25 June 2010

Published online in
Wiley Online Library (wileyonlinelibrary.com)
DOI: 10.1002/jmor.10894

JOURNAL OF MORPHOLOGY 000:000–000 (2011)

� 2011 WILEY-LISS, INC.



MATERIALS AND METHODS

For the osteological analysis, 120 specimens of C. latirostris
and C. yacare at different ontogenetic stages were analyzed:
100 specimens of C. yacare and 20 of C. latirostris were housed
at the herpetological collections of Museo Argentino de Ciencias
Naturales (MACN) ‘‘Bernardino Rivadavia’’ and Museo de La
Plata. Quantitative analysis was carried out on the skull of 37
specimens of different sizes of both species. The sample size for
each species was chosen according to the availability of ontoge-
netic series with complete skulls in the collections. The follow-
ing skull measurements were taken using a digital caliper (0.01
mm): total cranial length (measured dorsally along the sagital
axis from the tip of the premaxilla to the posterior margin of
the skull table); snout length (measured dorsally along the sagi-
tal axis from the tip of the premaxilla to the anterior margin of
the orbits); anterior snout width (measured dorsally and per-
pendicularly to the sagital at the premaxillary–maxillary
suture); posterior snout width (measured dorsally and perpen-
dicularly to the sagital at the anterior margin of the orbits);
and interorbital minimum width. The relationship between
these traits and the overall size, in the postnatal ontogeny in
both species of Caiman, was analyzed using linear regression.
For this purpose, the data were log10 transformed and bivariate
equations were calculated. The slope (b), intercept (log a), and
confidence intervals were calculated using ordinary least
squares regression (OLS) and standardized major axis
(Legendre and Legendre, 1998). Because of the high correlation
between the skull variables analyzed, similar results were
obtained with two methods; here we report OLS results.
For the myological cranial analysis, two subadult specimens

of C. latirostris and one subadult specimen of C. yacare were
analyzed. This material was provided by the staff of ‘‘El
Cachape’’ and ‘‘Proyecto Yacaré’’ in the provinces of Chaco and
Santa Fe of Argentina, respectively. The specimens were dis-
sected at the Laboratory of Vertebrate Anatomy at the Facultad
de Ciencias Naturales, Universidad Nacional de La Plata
(School of Natural Sciences) and also in the Herpetology
Department of Museo de La Plata, Argentina. All specimens
were obtained fresh, frozen, or fixed in 10% neutral buffered

formalin and sectioned using a scalpel. All dissections were
documented by digital photography. Attachment areas were
examined on the osteological material. The myological study
proceeded from the most superficial muscles to the deepest
ones, removing the jugal and quadratojugal bones, the postorbi-
tal processes, and finally part of the maxilla.

We follow Romer (1956) for osteological nomenclature and
Sedlmayr (2002) for the nomenclature of nerves and blood ves-
sels. The main cranial muscular groups were identified based
on the main muscle innervations (e.g., trigeminal, facial, glosso-
pharyngeal, hypoglossal nerves) following Iordansky (2000) and
Schumacher (1973). In the case of the adductor chamber, we fol-
lowed Holliday and Witmer (2007) (Tables 1 and 2). The relative
position of the ophthalmic, maxillary, and mandibular divisions
of the trigeminal nerve distinguish different groups of jaw
muscles, namely M. adductor mandibulae internus (MAMI), M.
adductor mandibulae externus (MAME), M. adductor mandibu-
lae posterior (MAMP), and M. constrictor internus dorsalis
(MCID). In the case of the trigeminal muscles, this paper
focuses primarily on the adductor musculature proper (i.e., M.
adductor mandibulae) and does not include the MCID.

RESULTS
Cranial Osteology

In dorsal view, the skull of C. latirostris has a
triangular outline with the lateral margins con-
verging anteriorly. In other caimans, the lateral
margin of the rostral area is wavy. In this view,
the premaxillary–maxillary curvature is practi-
cally absent (Fig. 2A,B). The lateral margins of the
skull in the postorbital region are straight or
slightly concave, diverging from one another poste-
riorly. In all specimens, the lateral processes of the
squamosal are short and posterolaterally oriented.
The posterior margin of the skull table is straight
and perpendicular to the sagittal plane (posterior
margins of supraoccipital and two-thirds of
squamosal, approximately). In adults, the supra-
temporal fenestra is small, irregular, and antero-
posteriorly elongated. In dorsal view, the anterior
opening of the temporal canal in the supratempo-
ral fenestra is vertically oriented and covered by
the squamosal. The infratemporal fenestra is tri-
angular in outline and its anteroposterior length is
half of the orbit (Fig. 2A). It is limited ventropos-
teriorly by the quadratojugal bone, which extends
along the posterior margin but does not reach the
posterodorsal corner of the fenestra. In the orbital
area, the interorbital isthmus is pronounced. The
interorbital surface is concave, and the medial
margin of the orbit describes a crest, which proj-
ects anteriorly across the prefrontal bone, lacrimal
bone, and maxillae, almost reaching the lateral
margin of the rostral area (Fig. 2A). In front of the
orbit, this crest (paired) extends medially, forming
a transversal ‘‘u’’ like structure. In occipital view
(Fig. 2D), the posterodorsal margin of the skull is
slightly concave at the supraoccipital, horizontal at
the medial portion of the squamosal, and ventrally
projected at the lateral part of the squamosal
bone. The paroccipital projections are laterally
short and horizontally oriented. The supraoccipital

Fig. 1. Cladogram showing the phylogenetic position of Cai-
man latirostris (modified from Brochu, 2003).

2 P. BONA AND J.B. DESOJO

Journal of Morphology



TABLE 1. Trigeminal muscles (Iordansky, 2000) in C. latirostris

Origin Insertion

M. adductor mandibulae
externus (Holliday and
Witmer, 2007)

Ventral surface of the
quadrate and quadratojugal
(its superficial pars contacts
the postorbital)

Aponeurosis coronar,
transiliens cartilage, and
dorsal border of surangular

M. adductor mandibulae
posterior (Holliday and
Witmer, 2007)

Ventral surface of the quadrate Medial border of
the articular, medial margin
of the angular, medial area
of the surangular, and
caudal portion of the
transiliens cartilage

M. aductor mandibulae
internus (Holliday and
Witmer, 2007)

M. pseudotemporalis
(5 M. Pseudotemporalis
superficialis and
profundus sensu Holliday
and Witmer, 2007)

Laterosphenoid Dorsal surface of
the transiliens cartilage

M. intramandibularis
(sensu Iordansky, 1964)

Transiliens cartilage
(intramandibular aponeurosis,
Iordansky 2000)

Medial surface of
the dentary, splenial,
angular and Meckelian
cartilage

M. pterygoideus dorsalis
(Holliday and Witmer 2007)

Medial and anterior margin
of the suborbital fenestra,
maxilla, prefrontal
and orbitonasal and
interorbital cartilages

Anterolaterally and
posteromedially to the
mandibular tendon

M. pterygoideus ventralis
(Holliday and Witmer 2007)

Dorsoposterior surface of
pterygoid and pterygoidal
aponeurosis (sensu
Iordansky, 2000)

Posterior and medial
border of the
retroarticular process

M. intermandibularis
(Holliday and Witmer, 2007)

Anterior half of each splenial The opposite splenial
bone, anteriorly and
in a medial raphe, posteriorly

Origins (dorsal attachments), insertions (ventral attachments),and terms followed in this study.

TABLE 2. Facial, glossopharyngeal, hypoglossal, and hypobranchial longitudinal muscles in C. latirostris

Origin Insertion

Facial muscles
(Iordansky, 2000)

M. constrictor colli An aponeurosis of
M. pterygoideus ventralis and
laterally to the first two
cervical vertebrae (sensu
Schumacher 1973)

Medial tendinous raphe
and posteroventral
tendinous zone of
the hyoids

M. depressor
mandibulae

Posterodorsal margin of
supraoccipital, squamosal,
and posterodorsal surface
of quadrate

Dorsal surface of the
retroarticular process

Glossopharyngeal muscles
(Schumacher, 1973)

M. branchiomandibularis
visceralis

Lateral margin of hyoids Anteroventral surface
of angular

Hypoglossal muscles
(Schumascher, 1973)

M. branchiomandibularis
spinalis

Basal end of the
Cornu branchiale I
of hyoids

Medial and dorsal
surface of splenial

M. hyoglossus Dorsolateral, posterior and
ventral border of the
posterior corner of
the hyoid

Connective raphe at the
base of the tongue
(its fibers are anteriorly
interdigitated forming
the tongue)

M. genioglossus Mandibular symphysis Anterior border of the
hyoid (its fibers extends
posterolaterally surrounding
the M. hyoglossus)

M. coracohyoideus Coracoid Posterior process of the hyoid
Hypobranchial longitudinal

muscles (Schumacher, 1973)
M. episternobranchiotendineus Sternum Medial surface and

posterodorsal margin
of the splenial

M. episternobranchialis Sternum Ventrolateral area of the
hyoid body, medially to
the cornu branchialis I

Origins (dorsal attachments), insertions (ventral attachments),and terms followed in this study.

OSTEOLOGY AND CRANIAL MUSCULATURE OF C. latirostris 3

Journal of Morphology



bone is low and wide, pentagonal, and forms the
ventromedial margin of the post-temporal fenestra,
which is much reduced in this species. The fora-
men magnum is delimited mostly by the exoccipi-
tal bones and by the basioccipital at the medial
ventral portion. The exoccipitals are sutured at the
midline and project ventrally, lateral to the basioc-
cipital tubera (as in many Caimaninae; Fig. 2D).
In occipital view, the subtemporal fossa is more
depressed than in other Caiman species (e.g., C.
yacare) and is limited mainly by the quadrate bone
dorsally and the pterygoid ventrally.

In palatal view, the palatine isthmus is present
and slightly displaced to the posterior sector of the
medial margin of the suborbital fenestrae (Fig.
2C). The suborbital fenestrae are limited by the
palatine medially and posteriorly, the pterygoid
posteriorly, the ectopterygoid posterolaterally, and
the maxilla anteriorly and anterolaterally. The
external surfaces of the dermal bones are sculp-
tured and covered with ridges and cells as in other
species of Caiman. This sculpturing is pronounced
on the skull and least developed on the lower jaw,
where it is strongly marked on the lateral surfaces
of the angular and surangular bones, posterior to

the external mandibular fenestra (Fig. 3A). The
number of mandibular teeth ranges from 17 to 19.
The length of the mandibular symphysis is vari-
able and extends to the alveoli fifth, fifth/sixth. As
in other caimans, the lateral margin of the dentary
bone in lateral view presents two stout flexures,
the first between alveoli first and fourth and the
second between fifth and tenth alveoli. The exter-
nal mandibular fenestra is delimited by the den-
tary anteriorly and anteroventrally (in small pro-
portion), the angular posteroventrally, and the sur-
angular posterodorsally. The extension of the
dentary along the ventral margin of the external
mandibular fenestra is variable in Caiman species
and in one specimen of C. latirostris (MACN
30566) the dentary did not delimit the fenestra.
The internal mandibular fenestra is delimited by
the angular ventrally, the articular posteriorly and
posteroventrally, and the coronoid anteriorly and
anteroventrally (Fig. 3B). The ovate foramen inter-
mandibularis caudalis is horizontally oriented and
delimited by the angular posteriorly and the sple-
nial anteriorly.

Basioccipital bone. In occipital view (Fig. 2D),
the basioccipital bone is wider and hexagonal in

Fig. 2. Skull of C. latirostris (MACN V 1420): A, dorsal; B, lateral; C, palatal; D, occipital views. Scale bar equals 5 cm. bo,
basioccipital; bsf, basisphenoid; ch, choanae; cf, carotid foramen; cq, cranioquadrate canal; eam, external auditory meatus; ect,
ectopterigoid; exo, exoccipital; fa, foramen aërum; fr, frontal; if, incisive foramen; it, infratemporal fenestra; j, jugal; la, lacrimal;
mx, maxilla; na, nasal; pa, parietal; pal, palatine; pf, prefrontal; pmx, premaxilla; po, postorbital; pt, pterigoid; ptf, postemporal fe-
nestra; q, quadrate; qj, quadratojugal, rc, rostral curvatures; rcr, rostral crest; sq, squamosal; so, supraoccipital; sof, suborbital fe-
nestra; f IX, f X, f XI, f XII, 9–128 cranial nerve foramens.

4 P. BONA AND J.B. DESOJO

Journal of Morphology



shape. It contacts the basisphenoid ventrally and
the exoccipitals laterally and dorsally. Together
with the basisphenoid, it delimits the single
medial opening and the paired lateral openings of
the Eustachian tubes ventrally. It forms the occipi-
tal condyle and the medioventral margin of the fo-
ramen magnum dorsally and extends anteriorly
forming the posterior floor of the braincase.

Exoccipital bone. In occipital view, each
exoccipital extends horizontally forming a short
paroccipital projection (Fig. 2D) and contacts the
squamosal dorsolaterally, the supraoccipital dorso-
medially, the quadrate ventrolaterally, and the
basioccipital ventromedially. In lateral view, each
exoccipital contacts the quadrate anterodorsally
and the basisphenoid anteroventrally. The exocci-
pitals also contact each other on the midline delim-
iting the ventrolateral, lateral, and dorsal margins
of the foramen magnum. The following foramina
open lateral to the foramen magnum: 1) Openings
for cranial nerves IX, X, XI, and XII. In C. latirost-
ris these are three horizontally aligned openings.
From medial to lateral, they correspond to the
opening for the XII2 branch which innervates
part of the neck muscles, a middle opening for the
XII1 branch which innervates the hyoglossus,
sternohyoideus, and sternothyroideus muscles
(see below), and the most lateral opening for
nerves IX, X, and XI. This last foramen is the
largest, and in all specimens of this species it

presents an internal bony septum that separates
the opening for the IX nerve (medial) from the
opening for the nerves X and XI (lateral). 2) Ca-
rotid foramen. This is most ventral in position,
located near the lateral margin of the exoccipital.
The internal carotid arteries pass through this fo-
ramen. 3) Cranioquadrate canal. This canal
extends between the paroccipital process and the
quadrate (Fig. 2D) from the middle ear cavity to
the occipital surface, where it opens on the medio-
ventral margin of the paroccipital process. It cor-
responds to the passage for the hyomandibular
branch of the facial nerve (VII; mainly the VII3
branch that innervates the M. depressor mandi-
bulae and another branch that innervates the
chorda tympani), the orbitotemporal artery, and
the lateral cephalic vein (Iordansky, 1973; tem-
poroorbital artery and vein sensu Sedlmayr,
2002).

Supraoccipital bone. The supraoccipital has a
triangular outline in occipital view (Fig. 2D). It
contacts the squamosal laterally and the exoccipi-
tal ventrally, together delimiting the post-temporal
fenestrae. These fenestrae provide the passage for
vessels that stem from the orbitotemporal artery
and vein (Sedlmayr, 2002). As in other Caimani-
nae, the supraoccipital bone extends on the poste-
rior surface of the skull table and in dorsal view
it contacts the parietal anterolaterally and the
squamosal posterolaterally. The dorsal surface is

Fig. 3. Lower jaw of C. latirostris (MACN V 1420): A, lateral; B, medial; C, dorsal views. Scale bar equals 5 cm. al, alveolous
(48, 58, 68); an, angular; ar, articular; cor, coronoid; de, dentary; emf, external mandibular fenestra; fa, foramen aërum; fic, foramen
intermandibularis caudalis; fim, foramen intermandibularis medius; fio, foramen intermandibularis oralis; imf, internal mandibular
fenestra; mg, meckelian groove; rp, retroarticular process; sa, surangular; sp, splenial.

OSTEOLOGY AND CRANIAL MUSCULATURE OF C. latirostris 5

Journal of Morphology



slightly concave with a poorly pronounced me-
dian crest. This crest is more pronounced in
adult specimens; this ontogenetic variation was
also observed in C. yacare.

Basisphenoid. The basisphenoid forms the an-
terior floor of the braincase and extends anteriorly
into the interorbital space forming the sphenoidal
rostrum. The basisphenoid is exposed in occipital
view, reaching the basioccipital bone dorsally and
pterygoid ventrolaterally. In posterolateral view, it
contacts the quadrate anterodorsally, the pterygoid
anteroventrally, the exoccipital bone posterodor-
sally, and the basioccipital bone posteroventrally.

Laterosphenoid. Each laterosphenoid forms
the anterolateral wall of the braincase and
extends dorsally forming the anteroventral area
of the medial wall of the supratemporal fossa.
In lateral view, it contacts the quadrate, ptery-
goid and prootic bone posteriorly, the pterygoid
ventrally, the basisphenoid anteroventrally, and
the frontal and postorbital dorsolaterally. To-
gether with the prootic bone it delimits the an-
terior part of the trigeminal opening (Fig.
4A,B). Laterally it presents a laterosphenoid
bridge, which in C. latirostris is a descending
process of the laterosphenoid that ventrally
forms a suture with the pterygoid, delimiting a
passage for the ophthalmic trigeminal branch
(V1; Fig. 4A). It also provides an attachment
surface for the M. pseudotemporalis profundus
(sensu Holliday and Witmer, 2007; Walker,
1990). The constitution and morphology of this
bridge is variable in crocodiles (Brochu, 1999:
64; figure 52) and even in Caiman (e.g., C. latir-
ostris, C. yacare). In C. latirostris, it is wide and
broadly sutured to the pterygoid (see below). As
in other Caiman species, the laterosphenoid
also forms a broad caudal bridge for the passage
of the supraorbital nerve (Holliday and Witmer,
2009) that articulates with the quadrate.

Prootic bone. As in other living crocodylians,
the prootic bone is not broadly exposed on the lat-
eral braincase wall and forms the posterior margin
of the trigeminal foramen.

Squamosal bone. Together with the postorbi-
tal, the squamosal delimits the supratemporal
fenestra ventrally. It contacts the postorbital and
parietal dorsally, supraoccipital and exoccipital
posteroventrally, and postorbital and quadrate an-
teroventrally. In occipital view, a subhorizontal
ridge is present that divides the surface of the
squamosal into two equivalent areas, the dorsal-
most portion of which is part of the attachment
site of the M. depressor mandibulae (Fig. 2D). In
lateral view, the squamosal forms the roof of the
tympanic cavity.

Parietal bone. Both parietal bones are fused at
the midline and form the anteromedial margin of
the supratemporal fenestra and the medial wall
of the supratemporal fossa. The parietal bone

contacts the frontal bone anteriorly, the postorbital
and squamosal bones laterally, and the supraocci-
pital bone posteriorly. Together with the supraocci-
pital, the parietal forms a shallow depression with
two smooth lateral ridges (Fig. 2A). These ridges
extend from the medial edge of the supratemporal
fenestra to the posterior margin of the skull table.

Postorbital bone. As in other crocodiles, this
bone forms the anterior part of the supratemporal
bridge at the anterolateral sector of the skull table
and also the anterolateral wall and margin of the
supratemporal fossa and fenestra, respectively. It
delimits the orbit posteriorly, by means of a de-
scending process that is sutured to the ascending
process of the jugal bone. Its contacts are with the
jugal ventrally, the squamosal and quadrate poste-
riorly, the laterosphenoid medially, and the frontal
anteriorly.

Frontal bone. Both frontal bones are fused at
the midline forming a single bone that delimits
part of the orbit medially and projects anteriorly
between the prefrontal bones. This projection
reaches the nasal bones in some specimens. It also
presents an interorbital isthmus and a concave
dorsal surface that together with the prefrontal
determines the medial orbital crest. The ventral
surface has a medial groove for the articulation of
the interorbital septum. The frontal contacts the
parietal dorsally and the postorbital posteriorly
(Fig. 2A).

Prefrontal bone. Each prefrontal bone is
located anteromedial to the orbit forming the ante-
rior part of the medial margin (crest) of the orbit.
The prefrontal contacts the frontal medially, the
nasal anteriorly, and the lacrimal laterally. It has
a ventromedial descending process, perpendicular
to the sagittal plane for the orbitonasal cartilagi-
nous septum. Ventrally, this process contacts pri-
marily with the palatine and the pterygoid.

Lacrimal bone. The lacrimal bone forms the
anterior margin of the orbit. The anterior margin
of the lacrimal (lacrimal–maxilla suture) possesses
a medial projection (Fig. 2A) that extends anteri-
orly between the nasal and maxilla. The lacrimal
gland is enclosed within the lacrimal bone and is
oriented longitudinally parallel to the sagittal
plane and opens posteriorly on the anterior margin
of the orbit. In dorsal view, the lacrimal contacts
the prefrontal and nasal medially, the jugal later-
ally, and the maxilla anteriorly.

Nasal bone. Each nasal is an elongate bone
that extends anteroposteriorly in the medial sector
of the snout reaching the external narial fenestrae
in some specimens (Fig. 2A). The nasal is a narrow
bone with lateral margins tapering anteriorly; in
some specimens these lateral margins extend into
the narial space and form a ‘‘heart-like’’ outline
for the narial opening. Both nasals form the roof of
the nasopalatine duct and posteriorly overlap the
frontals.

6 P. BONA AND J.B. DESOJO

Journal of Morphology



Vomer. Both vomers are slender and meet at
the midline forming the sulcus for the internasal
cartilaginous septum. The vomer extends posteri-
orly near the descending process of the prefrontal

bone. In ventral view, the vomers are covered by
the secondary palate.

Quadrate. The quadrate extends posterolater-
ally in the posterior portion of the skull and it is

Fig. 4. Detail of osteological cranial characters. A and B, Lateral view of the ventral surface of the quadrate: A, C. latirostris;
B, C. yacare. C and D, Dorsal view of the premaxilla: C, C. latirostris; D, C. yacare. E and F, Dorsal view of the retroarticular pro-
cess: E, C. latirostris; F, C. yacare. angc, anterior notch of the glenoid cavity; clsb, caudal laterosphenoid bridge; en, external nares;
fa, foramen aërum; fcno, supraorbital foramen; fV, trigeminal foramen; gc, glenoid cavity, if, incisive foramen; llsb, lateral lateros-
phenoid bridge; p1, piercing of the first lower teeth; rp, retroarticular process; stf, supratemporal fossa.

OSTEOLOGY AND CRANIAL MUSCULATURE OF C. latirostris 7

Journal of Morphology



sutured to surrounding bones, with the exception
of the otic sinovial articulation (see Holliday and
Witmer, 2008). The quadrate contacts the exoccipi-
tal and squamosal dorsally, the postorbital and
quadratojugal anterolaterally, and the laterosphe-
noid, prootic, pterygoid, basisphenoid, and exocci-
pital ventromedially. Posteroventrally, the quad-
rate forms the mandibular condyle. In occipital
view, a foramen aërum is present (see Brochu,
1999: 36, figures 24C and D). In lateral view, the
quadrate has a medial concave zone that repre-
sents the lateral floor of the middle ear cavity and
whose semicircular lateral margin supports the
tympanic membrane. Medially, the quadrate forms
the ventral, dorsal, and anterior margins of the
external auditory meatus, which is heart shaped.
In ventral view, two crests are present, A and B
sensu Iordansky (1964), for the attachment of the
M. adductor mandibulae externus and M. adduc-
tor mandibulae posterior. Crest A runs parallel to
the quadrate–quadratojugal suture and the medial
margin of the upper temporal fossa, while crest B
is vertically oriented posterior to the foramen for
nerve V and extends along the pterygoid. In C. lat-
irostris these crests are not prominent and crest B
tapers ventrally toward the posteroventral border
of the quadrate. The ventral surface of the quad-
rate projects anterodorsally to form the ventral
portion of the posterior wall of the supratemporal
fenestra. A small foramen is present in this area,
dorsal to crest A, for the passage of the supraorbi-
tal nerve (sensu Holliday and Witmer, 2009; Fig.
4A,B) and probably the middle cerebral vein.

Quadratojugal bone. The quadratojugal bone
forms the posterior margin of the infratemporal fe-
nestra, reaching its dorsal corner. In lateral view,
the quadratojugal forms the infratemporal arch to-
gether with the jugal and contacts the jugal ante-
riorly, the postorbital dorsally, and the quadrate
posteriorly.

Jugal bone. The jugal bone is an elongated
bone that delimits the ventral border of the orbit
and the infratemporal fenestra. In dorsal view, the
jugal contacts the lacrimal medially, the maxilla
anteriorly, and the quadratojugal posteriorly. Its
lateral margin is straight, but in lateral view, its
ventral margin is concave and projects dorsally via
an ascending process, which together with the post-
orbital delimits the orbit (Fig. 2A,B). As in other
crocodiles, its dorsal margin descends abruptly in
the postorbital region. In ventral view, the jugal is
positioned lateral to the maxilla, taking the form of
an anterior process that projects at least to the
level of the last two alveoli. In this view, the jugal
contacts the maxilla and ectopterygoid medially.

Maxilla. The maxilla contacts the jugal, prefron-
tal, and lacrimal posteriorly, the nasal laterally,
and the premaxilla posteriorly. Its dorsal surface
bears a crest that extends toward the anterior mar-
gin of the orbit. This crest extends anterolaterally

but does not reach the lateral border of the maxilla.
In its anterior part and in lateral view, the ventral
margin of this bone is convex with two slight cur-
vatures. The maxilla possesses 12 or 13 alveoli. In
palatal view, the maxilla contacts the premaxilla
anteriorly, the jugal posterolaterally, the ectopter-
ygoid posteriorly, and the palatine posterome-
dially. Together with the premaxilla and palatine,
the maxilla forms the anterior floor of the nasopa-
latine duct. The openings of the postvestibular
recess, anteromedially, and the caviconchal recess,
posterolaterally (Witmer, 1995), are present on
the medial surface of the maxilla.

Premaxilla. The premaxilla forms the antero-
lateral margin of the snout, contacting the maxilla
posteriorly. The premaxilla projects dorsomedially
and delimits the external naris forming a postero-
lateral ridge. In some specimens the premaxillae
contact each other dorsomedially, excluding the
nasals from the posterior margins of the external
nares. In palatal view, the premaxilla delimits the
incisive foramen, which in C. latirostris is heart or
teardrop shaped. The anterior ventral surface of
each premaxilla has a cavity that receives the first
mandibular tooth. In some specimens of C. lati-
rostris, this tooth pierces the palatal surface of
premaxilla (but never its dorsal anterior surface,
as in C. yacare or C. crocodylus; Fig. 4C,D).

Palatine bone. In palatal view, the palatine
bones contact one another at the midline and
delimit the suborbital fenestra medially. Anterior
to the fenestra, the palatines expand mediolater-
ally and possess a rounded outline that is wider
anteriorly.

Pterygoid. The pterygoids meet each other
along the midline both dorsally and ventrally,
forming the medial wall and roof of the middle
part, and all of the posterior part, of the nasopala-
tine duct. As in other Caimaninae, the secondary
choanae occupy the posterior third of the antero-
posterior length of the pterygoids and are bounded
by them. Internally, the wide ‘‘heart-shaped’’ choa-
nae are divided by a median bony septum formed
by pterygoids. This bony septum projects anteri-
orly, occupying almost the entire posterior half of
the palate. Posteriorly, the pterygoids project dor-
sally, reaching the lateral wall of the braincase
and forming a suture with the laterosphenoid
bridge, and in occipital view they contact the basi-
sphenoid. The suture between pterygoids and basi-
sphenoid is nearer to the medial opening of the
Eustachian tubes than in C. yacare.

Ectopterygoid. As in other crocodiles, the
ectopterygoid delimits the suborbital fenestra post-
erolaterally and contacts the maxilla anterolater-
ally, the jugal posterolaterally, the pterygoids
medially, and the descending process of the postor-
bital posteromedially.

Articular bone. The articular bone forms
the posterior margin of the internal mandibular fe-

8 P. BONA AND J.B. DESOJO

Journal of Morphology



nestra, most of the articular fossa, and the medi-
ally directed retroarticular process. This process is
trapezoidal in outline, with its posteromedial sur-
face rounded and its medial surface bearing a
small notch anterior to the glenoid cavity. The
mandibular foramen aërum is situated lateral to
this notch (Figs. 3C and 4E,F) and displaced from
the medial border of the retroarticular process.
The dorsal surface of this process is slightly con-
cave without the posterior protuberance present in
C. yacare. The glenoid cavity is bounded posteri-
orly, anteriorly, and medially by the articular. It is
subrectangular in shape, with the anterior and
posterior margins concave and the medial and the
lateral margins convex. The articular contacts the
surangular laterally and the angular posteroven-
trally.

Angular bone. In lateral view, the angular con-
tacts the surangular posterodorsally and the dent
anterodorsally, forming most of the ventral mar-
gin of the external mandibular fenestra and
part of the retroarticular process. In lateral
view, the posterior border of the lower jaw forms
an 1208 angle, approximately, so the mandible is
higher posteriorly. In lingual (medial) view, the
angular contacts the splenial anteriorly, the
coronoid anterodorsally, and the articular post-
erodorsally, forming part of the ventral margin
of the internal mandibular fenestra and delimit-
ing the foramen intermandibularis caudalis pos-
teriorly (Fig. 3B).

Surangular bone. As in other caimans, the
surangular bone projects posteriorly by means of a
process that almost reaches the posterior border of
the retroarticular process and forms the lateral
margin of the glenoid cavity (Fig. 3A,C). In lat-
eral view (Fig. 3A), the surangular bone contacts
the dentary bone anteroventrally, and the angu-
lar posteroventrally, forming the posterodorsal
margin of the external mandibular fenestra. The
suture between surangular bone and dentary
bone reaches the fenestra anterior to its postero-
dorsal corner, a general condition for alligator-
oids (Brochu, 1999). Medially, the surangular
contacts the splenial bone and the coronoid.

Dentary bone. As stated above, in C. latirostris
the length of the symphysis shows intraspecific
variation, extending to the level of the fifth, fifth–
sixth alveoli (Fig. 3C). The number of mandibular
teeth varies between 17 and 19. In lateral view,
the dentary bone contacts the surangular bone
dorsally and the angular bone ventrally. The dor-
sal margin of the dentary bone is wavy showing
two stout flexures, one positioned anteriorly, from
the first to fourth alveoli, and the second one pos-
teriorly from the fifth to the tenth alveoli. These
curvatures are also slightly developed in dorsal
view (Fig. 3C). In lateral view, the dentary bone
delimits the dorsal and anterior margins of the
external mandibular fenestra, a condition differ-

ent from that in C. jacare. Posteriorly, the den-
tary projects gradually in a dorsal direction and
contacts the splenial bone in medial view.

Splenial bone. As in all Caimaninae, the sple-
nial of alligatorids is excluded from the mandibu-
lar symphysis and projects dorsally to the Mecke-
lian groove (Brochu, 1999: 43, figure 31; adapted
from Clark, 1994: 66, 91, character 77). The sple-
nial extends along the medial surface of the man-
dible forming the medial wall of the Meckelian
canal. As in other caimanines, the splenial bears a
small foramen intermandibularis oralis (Fig. 3B;
see below) and contacts the coronoid posterodor-
sally and angular posteroventrally, delimiting to-
gether with the latter, the foramen intermandibu-
laris caudalis. Laterally, it contacts the dentary
bone, forming the medial border of the twelfth or
thirteenth alveoli.

Coronoid. The coronoid is a ventrally elongated
and crescent-shaped bone that delimits the Mecke-
lian fossa anteriorly and anteroventrally. Together
with a portion of the surangular bone, the postero-
dorsal surface of the coronoid serves as an attach-
ment area for the transiliens cartilage (Fig. 3B).
The coronoid contacts the splenial anteriorly and
the angular ventrally. As in Melanosuchus Gray
and other Caiman species, the foramen interman-
dibularis oralis medius is present in adult speci-
mens of C. latirostris.

Cranial Musculature
Trigeminal muscles. These muscles comprise

the adductor chamber, the main component of the
cranial musculature that takes up most of the tem-
poral fossae and the ventral sector of the orbit.
This musculature is traversed by several cranial
nerves and the muscular fibres are interdigitated,
making it difficult to establish the limits of each
muscle.

MAME. The MAME occupies the anterolateral
portion of the infratemporal fossa. (Fig. 5A) It is
attached to the ventral surface of the quadrate
and quadratojugal bone, passes ventrolaterally to
the jugal bar and inserts mainly on the dorsal
margin of the surangular bone and transiliens car-
tilage (Schumacher, 1973), from the coronoid crest
to the anterior sector of the glenoid cavity. Part of
the attachment area on the ventral surface of the
quadrate is formed by the quadrate aponeurosis
(Iordansky, 2000), which is also attached to crests
A and B (Iordansky, 1964) and vertically oriented.
In C. latirostris, the MAME is divided into three
superficial, medial, and deep main parts (Ior-
dansky, 1964; Van Drongelen and Dullemeijer,
1982). Iordansky (2000) considered this muscle to
be formed by two muscular packages in crocodiles,
the M. adductor mandibulae externus superficialis
(5 superficialis 1 medialis sensu Iordansky, 1964
and Van Drongelen and Dullemeijer, 1982), and

OSTEOLOGY AND CRANIAL MUSCULATURE OF C. latirostris 9

Journal of Morphology



profundus. The deepest pars originates at the
ventral margin of the parietal and squamosal
bones, runs vertically and inserts into the coronar
aponeurosis (see Iordanky, 2000; table 1) and post-
erodorsally to the transiliens cartilage. In lateral
view, this pars is anterior to the medial pars. The
latter is represented by a muscular mass situated
dorsomedially to the superficial pars. Its fibers
extend from the ventral surface of the quadrate
lateral to crest A, running parallel and obliquely
oriented in a dorsomedial–ventrolateral direction.
In its posterior part, the separation between
MAME and MAMP is not clear because their fibers
are interdigitated. The medial pars attaches medi-
ally to the pars superficialis and anteriorly to the
mandible by the coronar aponeurosis (see Iordan-
sky, 2000; figure 1). In lateral view, the superficial
pars is exposed as a muscular mass lateral to the
medial pars; it is attached to the descending pro-
cess of the quadratojugal–quadrate and contacts
the postorbital (sensu Van Drongelen and Dulle-

meijer, 1982). Its fibers are dorsomedially–ventro-
laterally oriented and insert mainly on the dorsal
border of the surangular.

MAMP. Together with MAME, this muscle occu-
pies the dorsal and posterior portion of the infra-
temporal fossa (Fig. 5A,B). Proximally the MAMP
is positioned lateral to the V3 trigeminal nerve
branch. This muscle originates on the ventral sur-
face of the quadrate by the quadrate aponeurosis
(sensu Iordanzky, 2000; ‘‘tendons A and B’’ of Ior-
dansky, 1964 or ‘‘aponeuroses II and IV’’ sensu Van
Drongelen and Dullemeijer, 1982: 347) and
attaches to the medial border of the articular by
means of the subarticular aponeurosis, to the
medial margin of the angular by the angular apo-
neurosis, and to the medial area of the surangular
and caudal portion of the transiliens cartilage, by
the coronar aponeurosis (Iordansky, 2000; figure
1). The MAMP is also attached to the Meckel’s car-
tilage and occupies the Meckelian fossa, covering
the external mandibular fenestra; at this level it is

Fig. 5. Cranial muscles in Caiman. A–C, Lateral view of trigeminal muscles in C. latirostris; D and E, lateral view of M. depres-
sor mandibulae and M. pterygoideus ventralis. D, C. latirostris and E, C. yacare. MAME, M. adductor mandibulae externus;
MAMIi, M. intramandibularis; MAMP, M. adductor mandibulae posterior; MAMIPst, M. pseudotemporalis; MAMIPtd, M. pterygoi-
deus dorsalis; MAMIPtv, M. pterygoideus ventralis; MDM, M. depressor mandibulae; tc, transiliens cartilage.

10 P. BONA AND J.B. DESOJO

Journal of Morphology



attached by an aponeurosis-like fibrous connective
tissue. Its fibers are mostly ventrolaterally ori-
ented but slightly slanted posteriorly.

MAMI. The M. pseudotemporalis is attached to
the laterosphenoid. Its fibers run dorsoventrally
and are placed medial to the V2 and anteriorly to
the V3 trigeminal branches (Fig. 5A–C). The proxi-
mal portion of this muscle (near to the origin) is
anteromedial to the deep pars and anterior to the
medial pars of MAME and attached to the dorsal
surface of the transiliens cartilage. As in other
crocodiles, in C. latirostris we recognized two por-
tions. The first is slender and anterolaterally posi-
tioned, attached to the laterodorsal surface of the
laterosphenoid and inserted onto the dorsal surface
of the transiliens cartilage. The second was deeper,
positioned medial to the V3 branch of the trigemi-
nal nerve, and attached to the laterosphenoid
bridge and inserted on the coronar aponeurosis
sensu Iordansky (2000). Holliday and Witmer
(2007) identified these two pars as M. pseudotem-
poralis superficialis (which comprises the M. intra-
mandibularis) and M. pseudotemporalis profundus.

M. intramandibularis. This muscle is attached
to the fan-shaped intramandibular aponeurosis
(Iordansky, 2000; figure 1) that projects anteroven-
trally into the Meckelian canal from the ventral
surface of the transiliens cartilage (Fig. 5A–C). Its
fan-shaped fibers are anteroventrally oriented and
insert on the medial surface of the dentary bone,
splenial bone, angular bone, and Meckelian carti-
lage. This cartilage is a hyaline longitudinal bar
that extends along the ventral border of the man-
dible at the level of the mandibular symphysis.
Holliday and Witmer (2007) considered M. intra-
mandibularis as a mandibular portion of the M.
pseudotemporalis superficialis.

M. pterygoideus dorsalis. This muscle is attached
to the medial and anterior margin of the suborbital
fenestra at the palatine and to the maxilla and pre-
frontal bones and the orbitonasal and interorbital
cartilages (Fig. 5A–C). Its fibers run mainly in an
anteroposterior direction, occupying the suborbital
fossa and inserting anterolaterally and posterome-
dially to the mandibular tendon, dorsal to the deep-
est pars of MAMI pseudotemporalis.

M. pterygoideus ventralis. This muscle is situ-
ated in the ventral and posterior parts of the infra-
temporal fossa and the posterior and posteroven-
tral parts of the mandible (Figs. 5A,B,D,E, and
6A). It attaches to the posteriodorsal surface of the
pterygoid and the pterygoidal aponeurosis (sensu
Iordansky, 2000). This aponeurosis is formed by
three sheets, two vertical (lateral and medial)
sheets connected by one horizontal (ventral) sheet.
The ventral horizontal sheet is attached to the pos-
terior margin of the pterygoid, the medial sheet is
dorsally attached to a medial sheet of the quadrate
aponeurosis and ventrally to the ventral sheet.
The lateral sheet is anteriorly attached to the lat-

eral margin of the pterygoid and the lateroposte-
rior margin of the ectopterygoid and extends poste-
riorly and continuously to the ventral sheet. The
fibers of the M. pterygoideus ventralis extend as
several fan-shaped sheets and insert at the mandi-
ble by the angular and retroarticular aponeurosis
onto the posterior and medial border of the retro-
articular process.

M. intermandibularis. This muscle is attached
to the anterior half of each splenial bone, occupy-
ing the anterior intermandibular space on the dor-
sal part of the medial surfaces of the splenial
bone. Anteriorly, its fibers run transversally from
hemimandible to hemimandible; posteriorly, the
fibers insert in a medial raphe.

Facial muscles.
M. constrictor colli. This muscle is divided into

two portions, one superficial and the other deep
(Figs. 5D,E, 6A,B). The superficial portion is repre-
sented by a pars oralis and a pars aboralis. The
pars oralis is attached to an aponeurosis of M.
pterygoideus ventralis, and its fibers run transver-
sally to the sagittal plane behind the M. interman-
dibularis and insert onto a medial tendinous
raphe. The deep portion, M. constrictor colli pro-
fundus (5 M. interhyoideus of Iordansky, 2000)
attaches laterally to the first two cervical verte-
brae (sensu Schumacher, 1973) and inserts on the
posteroventral tendinous zone of the hyoids. Its
horizontal fibers are perpendicular to the sagittal
plane and surround the trachea.

MDM. In occipital view, the MDM is ventrally in
contact with the superficial neck musculature (Fig.
5D). It attaches to the posterodorsal margin of the
supraoccipital and squamosal and to the postero-
dorsal surface of the quadrate. The fibers of the
MDM insert on the dorsal surface of the retroartic-
ular process. In lateral view, it is rectangular
shaped with the fibers obliquely oriented at an
angle of approximately 458.

Glossopharyngeal muscles
M. branchiomandibularis visceralis. This muscle

is attached laterally to the hyoids via an aponeuro-
sis lateral to the M. hyoglossus, in the insertion
zone of the M. hyoglossus on the hyoids (Fig.
6A,B). The fibers of M. branchiomandibularis vis-
ceralis run anteriorly and slightly obliquely and
insert on the anteroventral surface of the angular,
covering in part the lingual foramen.

Hypoglossal muscles.
M. branchiomandibularis spinalis. This muscle

is attached to the basal end of the Cornu bran-
chiale I of the hyoid apparatus (Schumacher, 1973:
185; figure 54). In C. latirostris, the fibers of this
muscle run parallel and insert anteriorly on the
medial and dorsal surface of the splenial (Fig.
6A,B).

M. hyoglossus. In C. latirostris, this muscle is
formed by a pars medialis and a pars lateralis.
The latter pars is attached to the dorsolateral and

OSTEOLOGY AND CRANIAL MUSCULATURE OF C. latirostris 11

Journal of Morphology



posterior parts of the posterior corner of the hyoid
(considered as the Cornu branchiale II of other
sauropsids; see Schumacher, 1973), surrounding it.
Its short fibers insert on a connective raphe at the
base of the tongue. The better developed pars
medialis is attached to an aponeurosis on the ven-
tral border of the posterior corner of the hyoid. Its
fibers run obliquely (medially) and are anteriorly
interdigitated forming the tongue (Fig. 6B).

M. genioglossus. This muscle is attached to the
mandibular symphysis and, like M. hyoglossus,
comprises both a pars medialis and a pars latera-
lis. The narrow pars medialis extends posteriorly
toward the anterior border of the hyoid, where it
inserts by means of a tendon. The pars lateralis
extends posterolaterally and surrounds the M. hyo-
glossus (Fig. 6A,B).

Hypobranchial longitudinal muscles.
M. coracohyoideus. The fibers of this muscle are

arranged in two longitudinal bundles lateral to the
M. episternobranchiotendineus and M. episterno-
branchialis, at both sides of the trachea (Fig. 6A).
The fibers of M. coracohyoideus are attached to
the coracoid, extend alongside the trachea and
insert mainly on the posterior process of the hyoid
or Cornu Branchial II (Fig. 6A,B).

M. episternobranchiotendineus. This muscle is
attached to the sternum and extends anteriorly to
the medial surface and posterodorsal margin of the

splenial bone. Its longitudinal fibers are positioned
lateral to M. episternobranchialis, and together
with the latter cover the ventral surface of the tra-
chea. In its anterior sector the fibers of the M.
episternobranchiotendineus are laterally oriented
(Fig. 6A,B).

M. episternobranchialis. This muscle is attached
to the sternum and extends anteriorly as two bun-
dles of longitudinal fibers medial to the M. epister-
nobranchiotendineus. M. episternobranchialis (Fig.
6A,B) inserts on the ventrolateral area of the
hyoid body medially to the cornu branchialis I.

Skull Measurements

As a result of the allometric analysis, we
obtained a high positive correlation between skull
traits and the overall skull size (Table 3). In both
Caiman species the snout length increases with
positive allometry through ontogeny (Fig. 7A; Ta-
ble 3). The elongation of the snout occurs in the
same way in both species from small-sized to big-
sized specimens, so both species are practically
indistinguishable from each other by their snout
relative length in each ontogenetic state. Contrary
to C. yacare, in C. latirostris, the interorbital space
increases isometrically while increasing the skull
length, so the relative position of the orbits in the
midline would be determined in young specimens

Fig. 6. Ventral view of cranial muscles in C. latirostris. A, superficial dissection; B, deeper dissection. h, hyoid; MAMIPtv, M.
pterygoideus ventralis; Mbs, M. branchiomandibularis spinalis; Mbv, M. branchiomandibularis visceralis; MCH, M. coracohyoideus;
MCp, M. constrictor colli profundus; MEB, M. episternobranchiotendineus; MEBT, M. episternobranchiotendineus; Mgl, M. genio-
glossuslateralis; Mgm, M. genioglossus medialis; MH, M. hyoglossus; t, trachea.

12 P. BONA AND J.B. DESOJO

Journal of Morphology



and remains invariable in relation to the anterior–
posterior growth of skull during ontogeny (Fig. 7B;
Table 3). C. latirostris is the widest snouted Cai-
man. This condition in the posterior sector of the
snout (anteorbital width) is probably established
early in ontogeny and differs from that of C.
yacare from the first ontogenetic states (Fig. 7C).
Nevertheless while in C. yacare the anterior snout
width increases isometrically with the skull length
(probably establishing the final snout shape in
young specimens), in C latirostris this growth
shows positive allometry. This positive allometric
relationship with the anterior snout width and the
skull length could be determining a change of the
snout shape during ontogeny and the final charac-

teristic broad-snouted shape of this species would
be establishing late in ontogeny (Fig. 7D). These
hypotheses would be tested in future morphomet-
ric analysis in a bigger sample of specimens of
these two Caiman species.

DISCUSSION

The focus of this study was the anatomical anal-
ysis of the cranial osteology and myology of C. lati-
rostris. Compared with other extant caimans, C.
latirostris shows morphological differences at skull
level that are discussed below. Generally, the
cranial morphology of C. latirostris is an overall
triangular outline in dorsal view, with the lateral

TABLE 3. Results of the regression analysis of skull variables measured in relation to total skull as independent variable

Species Dependent variables b CI log a r2 P Allometry

C. yacare Snout length 1.10 1.07–1.13 20.45 0.99 <0.05 1
C. latirostris Snout length 1.14 1.08–1.19 20.55 0.99 <0.05 1
C. yacare Anterior snout width 1 0.91–1.09 20.53 0.96 <0.05 No
C. latirostris Anterior snout width 1.16 1–1.32 20.80 0.96 <0.05 1
C. yacare Posterior snout width 1 0.95–1.06 20.35 0.98 <0.05 No
C. latirostris Posterior snout width 1.07 0.93–1.22 20.41 0.96 <0.05 No
C. yacare Interorbital width 1.18 1.04–1.32 21.46 0.95 <0.05 1
C. latirostris Interorbital width 1.08 0.94–1.22 21.19 0.97 <0.05 No

Fig. 7. Graphs of allometric equations calculated for different skull variables measured on 37 Cai-
man species differing in skull size.A, snout length;B, interorbital minimumwidth;C, posterior snout
width;D, anterior snout width. The data are presented in logarithmic scale. Solid line: estimated allo-
metric equation; white squares: C. latirostris specimens; black squares: C. yacare specimens.

OSTEOLOGY AND CRANIAL MUSCULATURE OF C. latirostris 13

Journal of Morphology



margins converging in the snout region. Unlike
the condition in C. yacare and C. crocodylus, the
lateral curvature of the premaxilla–maxilla is
slightly marked in lateral view and absent in dor-
sal view. The rostral crests of C. latirostris are
well defined, and the medial flange of the orbits
extends as a continuous crest on the prefrontal,
the lacrimal, and the maxilla. This pattern is simi-
lar to the one in Melanosuchus niger (Spix), and
the presence of very prominent rostral crests may
be a shared character supporting the sister group
relationship between C. latirostris and M. niger
(Norell, 1988; Poe, 1997; Brochu, 1999). In C.
yacare and C. crocodylus, the medial crest of the
orbits is not prominent and extends anteriorly by
a short crest through the prefrontal and lacrimal
only. The occlusal pattern is the same in all alliga-
torids, with the dentary teeth occluding lingual to
the maxillary toothrow. Nevertheless, some slight
variation exists among the species of caimans, and
in C. latirostris the first dentary teeth occlude pos-
terior to the first tooth of the premaxilla such that
never pierce the dorsal surface of this bone. In all
specimens in which these teeth reach the upper
jaw when the mouth is closed, the corresponding
perforations are seen though the narial openings
in the floor of the nasal cavity (Fig. 4C). In C.
yacare and C. crocodylus, the first tooth occludes
anteriorly, and when these teeth pierce the pre-
maxilla, the perforations are anterior to the narial
opening, on the dorsal surface of the bone (Fig.
4D). In many specimens of these species, the pos-
terior surface of the first lower tooth perforates
the anterior wall of the nasal cavity but never the
floor of the latter. Another difference between C.
latirostris and C. yacare is that the subtemporal
fossa is less wider in C. latirostris, such that in
occipital view the pterygoid–basisphenoid suture is
near the basisphenoid–basioccipital suture. The
higher position of the subtemporal fossa in C.
yacare is related to the larger size of the M. ptery-
goideus dorsalis in this species. Similarly, and in
contrast to C. yacare, in C. latirostris the lateral
bridge of the laterosphenoid is complete in all
studied specimens, and it is formed by a descend-
ing process of the laterosphenoid that is widely
sutured to the pterygoid ventrally (Holliday and
Witmer, 2009). Although the conformation and
morphology of this bridge is variable in crocodiles
(Brochu, 1999: 64; figure 52), in Caiman, this vari-
ation could be related to the anteroposterior exten-
sion of the ventral end of the laterosphenoid lat-
eral process, which in C. yacare is narrow and not
sutured to the pterygoid. By contrast, in C. latir-
ostris the caudal bridge of the laterosphenoid is
broadly sutured than the quadrate. The presence
of this bridge is an ancestral condition of Alligator-
idae that is present in all Caimaninae extant taxa.
Posterolaterally to this bridge, on the ventral sur-
face of the quadrate, two crests (A and B, Iordan-

sky, 1964) correspond to the insertion of several
portions of the adductor muscles (MAME and
MAMP). Although these crests occur in all croco-
diles, their relative size shows intraspecific varia-
tion in caimans. Anteriorly, crest A surrounds the
posteroventral margin of the internal supratempo-
ral fenestra. In C. latirostris, this crest is ventral
to the foramen for the passage of the supraorbital
nerve (sensu Holliday and Witmer, 2009) and prob-
ably the middle cerebral vein (Fig. 4A,B). In C.
yacare, the relative position of this crest shows
intraspecific variation, but it always located dorsal
to or at the same level as this foramen, and never
ventral to it as in C. latirostris (Fig. 4). Interspe-
cific variation of mandibular bones was recorded in
several structures of Caiman. In dorsal view, the
glenoid cavity of C. latirostris possesses only a
slight notch on the anterior margin (Fig. 3C), dif-
fering from the condition present in C. yacare, in
which this anterior notch is pronounced, so that
the glenoid cavity has a biconvex outline. In addi-
tion, the extension of the dentary bone along the
ventral margin of the external mandibular fenes-
tra also shows interspecific variation. In C. latir-
ostris, the dentary bone is not extended as in C.
yacare, forming a small anterior part of the ven-
tral border of this fenestra, or even being excluded
from this margin in some specimens.

Although the anatomy of jaw muscles of living
crocodiles follow the same general ‘‘Bauplan’’ (Ior-
dansky, 2000), and alligatorids seem to have a sim-
ilar pattern of cranial musculature, this study
revealed some differences with respect to previ-
ously published descriptions of caiman myology
(Iordansky, 1964, 2000; Schumacher, 1973, 1985;
Van Drongelen and Dullemeijer, 1982; Cleuren
and De Vree, 1992, 2000; Holliday and Witmer,
2007). The anterior and posterior portions of the
pars profunda of the MAME of C. crocodylus
described by Van Drongelen and Dullemeijer
(1982) was not observed in C. latirostris. Further-
more, in the latter species, this pars is attached to
the parietal and squamosal, and not only to the
parietal as in other crocodiles. In C. crocodylus,
the superficial pars of MAME (sensu Iordansky,
2000) is attached to the quadrate (lateral to crest
A), quadratojugal, and postorbital bones, but in C.
latirostris this muscle did not reach the postorbi-
tal. The M. pterygoideus dorsalis in C. latirostris
did not reach the pterygoid and lacrimal (Holliday
and Witmer, 2007), and contrary to the case of C.
crocodilus (Van Drongelen and Dullemeijer, 1982),
the M. pterygoideus ventralis attaches to the pos-
terodorsal surface of the pterygoid and the ptery-
goid aponeurosis, without contacting the dorsal
and ventral surface of the pterygoid margin. In C.
latirostris, the M. intermandibularis is attached to
the anterior half of the splenial and posteriorly
inserts by a medial raphe that serves as attach-
ment zone for M. constrictor colli. An additional

14 P. BONA AND J.B. DESOJO

Journal of Morphology



difference observed in C latirostris and C. yacare,
with respect to the available information published
for other crocodiles (e.g., Iordansky, 2000), is that
the M. depressor mandibulae attaches to the pos-
terodorsal margin of the supraoccipital, squamosal,
and the posterodorsal surface of quadrate. In lat-
eral view in C. latirostris, this muscle is subrec-
tangular and its fibers are obliquely oriented at an
angle <458, differing from C. yacare in which this
muscle is subtriangular and has oblique fibers ori-
ented at an angle �458 (Fig. 5D,E). The cranial
musculature of C. latirostris also differs from that
of other alligatorids in the following characteris-
tics: 1) presence of a medial notch in the anterior
margin of M. constrictor colli profundus; 2) the
attachment area of M. depressor mandibulae does
not include the parietals, as in Alligatorinae; and
3) the attachment area for M. branchiomandibula-
ris visceralis is positioned more anteriorly than in
Alligator.

These cranial muscles have been previously
described mainly for A. mississippiensis, and the
paucity of information about this musculature in
caimans makes it difficult to analyze its morpholog-
ical variability. The variability of cranial morphol-
ogy in caimans needs to be reanalyzed within the
phylogenetic context of the Caimaninae, first
increasing the number of specimens and taxa and
then analyzing the implications of this variation in
a morphofunctional context. Furthermore, although
the variation of cranial morphology observed here
allows the recognition of potentially diagnostic
(mainly osteological) characters, these hypotheses
of homology should be phylogenetically tested to
clarify their role in the evolutionary history of mod-
ern caimans.

As stated above, C. latirostris is the most
extreme broad-snouted form among the Caiman
species. This cranial shape is unique among extant
Caimaninae (Fig. 1), and probably a reversal to
the condition present in basal Globidonta alligator-
oids (sensu Brochu, 1999). The rostral elongation
of the skull of most of the extant Caimaninae spe-
cies, not present in C. latirostris, increases the dis-
tance between the snout tip and the articular con-
dyle. This general morphology could give a greater
and faster movement for a given aperture angle of
the mouth (Monteiro et al., 1997). This is probably
an important feature related with the sideways
movements of the head during underwater ‘‘fish
catching.’’ Furthermore, the major height of the
subtemporal fossa in C. yacare is related to the
larger size of the M. pterygoideus in this species,
and could be related with an increased capacity to
keep the prey in the mouth during feeding. The
broad and short skull of C. latirostris could be ad-
vantageous for durophagy, a type of diet proposed
for this species (Diefenbach, 1979, 1987). Monteiro
et al. (1997) pointed out that an increase of the
distance between the origin and insertion of the

M. depressor mandibulae observed in posthatching
Caiman specimens allows a greater extent of con-
traction and more control over the mandibular
joint. However, the different angle of the fibers’
orientation of the M. depressor mandibulae
between C latirostris and C. yacare (Fig. 5D,E)
could correspond to a lower force needed to open
the mouth in C. latirostris and thus with less
aquatic habits and type of diet for this species. C.
latirostris is often found in slow-moving water in
dense forest, although a wider variety of habitat
types can be used when its range does not overlap
with that of C. yacare. Nevertheless, these appreci-
ations should be evaluated in a morphofunctional
context, which is beyond the scope of the present
analysis.

ACKNOWLEDGMENTS

The authors are grateful to the curators of the
Herpetological Collections, JD Williams (Museo de
La Plata) and J Faivovich (Museo Argentino de
Ciencias Naturales ‘‘Bernardino Rivadavia’’) for
allowing us to study the specimens under their
care. Thank also to the staff of ‘‘El Cachape’’
(Chaco province) and ‘‘Proyecto Yacaré’’ (Santa Fe
province) of Argentina who provided the C. yacare
and C. latirostris specimens for dissections. The
authors are grateful with R Battler and I Olivares
for their comments and suggestions that improved
this manuscript, M Tomeo and P Motta for the
drawings and the design of the figures. This study
was financed by the Agencia Nacional de Promo-
ción Cientı́fica y Tecnológica, PICT N8473 directed
by JB Desojo.

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