has a prominent lateral crest. The radius and ulna are completely fused.
A bony prepollex is present in both sexes. The metacarpals are about
equal in length. The phalangeal formula is 2-2-3-3; the terminal
phalanges are claw-shaped.
_Pelvic Girdle._--The ilia are long, slender, and slightly curved. A
thin ridge projects laterally from the dorsal edge of the posterior
one-half of each ilium. The ilial prominence is large and knoblike when
viewed from above. The anterior edge of the ilial prominence is at the
level of the anterior edge of the acetabular border. The dorsal
acetabular expansion is small. The pubis is slender, and the ischium is
elevated and robust.
_Leg and Foot._--The slightly curved femur has a distinct crest
proximally on the posterior surface. The nearly straight tibio-fibula is
slightly longer than the femur. The tibial and fibial elements are
completely fused but have a distinct cleft between them. A small foramen
exists at the mid-length of the tibio-fibula. The fibulare (calcaneum)
is much more robust than the tibiale (astragalus). The prehallux is
large and flat. The metatarsals of the third, fourth, and fifth digits
are equal in length; the metatarsal of the second is somewhat shorter,
and that of the first is much shorter. The phalangeal formula is
2-2-3-4-3; the terminal phalanges are claw-shaped.
_Developmental Cranial Morphology of Smilisca baudini_
The following description of development of the skull of _Smilisca
baudini_ is based on the examination of 12 cleared and stained
specimens. In table 3 the cranial bones are listed in the left hand
column in the approximate order of their appearance in the young frogs.
Across the top of the table selected specimens designated by
developmental stage or snout-vent length are listed. It should be noted
that although each individual, from left to right, has an increasing
number of ossified bones, the correlation with increasing size is
imperfect; the precise ages of the individuals are unknown.
The first bones to appear are the septomaxillaries, frontoparietals,
part of the exoccipital, and the parasphenoid in developmental stage 40.
The frontoparietals are represented by two slender ossifications
dorsomedial to the orbits; the septomaxillaries are present as small
ossifications anterior to the nasal capsules (Pl. 1A). The parasphenoid
is present as a faint median ossification, and the exoccipital shows
some ossification.
Table 3.--The Order of Occurrence of Cranial Ossifications in the
Skull of Smilisca baudini. Where Numbers Are Divided by a Slash
Mark, the Left and Right Symbols Correspond to the Left and
Right Sides of the Skull, Respectively.
=====================+=====+=====+=====+=====+=====+=====+====
Bone |Stage|Stage|12.6 |13.9 |32.0 |27.0 |20.1
| 40 | 44 | mm. | mm. | mm. | mm. | mm.
---------------------+-----+-----+-----+-----+-----+-----+----
Frontoparietal | X | X | X | X | X | X | X
Parasphenoid | X | X | X | X | X | X | X
Septomaxillaries | X | X | X | X | X | X | X
Exoccipitals | X | X | X | X | X | X | X
Squamosals | -- | X | X | X | X | X | X
Premaxillaries | -- | X | X | X | X | X | X
Maxillaries | -- | X | X | X | X | X | X
Nasals | -- | -- | X | X | X | X | X
Pterygoids | -- | -- | X | X | X | X | X
Vomers | -- | -- | -- | X | X | X | X
Palatines | -- | -- | -- | X | X | X | X
Quadratojugals | -- | -- | -- | X | X | X | X
Ethmoid | -- | -- | -- | -- | X | X | X
Columellas | -- | -- | -- | -- | X | X | X
Supraorbital Flanges | -- | -- | -- | -- | -- | X | X
Prooetics | -- | -- | -- | -- | -- | -- | X
Vomerine Teeth | -- | -- | 1/1 | 4/3 | 5/5 | 3/3 | 5/4
Maxillary Teeth | -- | 0/7 | 3/5 | 6/5 |30/31|30/26|37/36
Premaxillary Teeth | -- | 2/4 | 3/3 | 5/5 | 7/6 | 8/6 | 8/7
---------------------+-----+-----+-----+-----+-----+-----+----
The dentigerous bones are among the most rapidly developed, although not
the first to appear. They are present in developmental stage 44 before
metamorphosis is completed. The maxillaries bear a few teeth anteriorly
and are ossified posteriorly to a point one-third of the distance from
the anterior to the posterior edge of the orbit. Ossification lengthens
the posterior termini of the maxillaries to the posterior edge of the
orbit. In front of the anterior margin of the orbit, bone is
proliferated dorsal to the main axes of the maxillaries and forms
moderate dorsal maxillary flanges. The premaxillaries appear
simultaneously with the maxillaries. Initially they are widely separated
medially from each other, and laterally from the developing maxillaries;
each bears two or three teeth, large dorsally blunt alary processes, and
small palatine processes. The median and lateral edges of the prenasal
processes lengthen heterochronously, causing the median edges to be
longest and to lie slightly dorsal to the level of the septomaxillaries.
After the maxillaries and premaxillaries develop, the vomers appear as
small horizontal ossifications anterior to the parasphenoid.
Ossification begins in the lateral flanges, then in the prevomerine
processes, and lastly in the posterior dentigerous parts of the bones;
the prevomerine processes are the last parts of the vomers to ossify
completely.
Initially the frontoparietals are present as thin rods of ossification
dorsomedial to the orbits; the frontoparietals extend from the anterior
to the posterior end of the orbit by developmental stage 44. The
anterior ends of the bones remain thin and pointed; ossification
progresses medially from the midpoint of the length of the orbit and
posteriorly to the level of the exoccipital; a median center of
ossification joins the frontoparietals posteriorly, thereby forming the
posterior border of the frontoparietal fontanelle. The supraorbital
flanges of the frontoparietals do not appear until all other cranial
bones are ossified, or nearly so. The most rapid ossification begins
laterally at the posterior edge of the orbit and decreases anteriorly
over the posterior half of the orbit. This differential rate of
proliferation of bone results in the pattern of development of the
supraorbital flanges shown in figure 7. The nasals appear as
thin slivers of bone half way between the anterior ends of the
frontoparietals and the end of the snout. As ossification proceeds the
nasals assume a triangular shape in dorsal view. The anterior ends are
pointed; the lateral margins are parallel to the maxillaries. The
posteromedial points do not reach the lateral margins of the ethmoid,
and the maxillary processes extend about three-fourths the distance from
the bodies of the nasals to the maxillaries. Following the union of the
frontoparietals posteriorly, the nasals widen anteriorly and are
narrower at the midpoints of their long axes than anteriorly or
posteriorly. With further ossification the maxillary processes extend to
the maxillaries and form complete bony anterior margins to the orbits;
the mid-parts of the nasals widen (Pl. 1B).
[Illustration: FIG. 7. Developmental sequence of the frontoparietal
fontanelle and associated bony elements in _Smilisca baudird_:
(A) KU 60026, x5; (B) KU 85438, x4; (C) KU 26328, x3;
(D) KU 68184, x2.3.]
The parasphenoid is the first of the palatal bones to appear. At
metamorphosis the bone is well developed; the anterior tip is situated
just in front of the anterior edge of the orbit, and posteriorly the
lateral processes extend laterally beyond the ossified parts of the
auditory region. The pterygoids do not appear until metamorphosis, when
ossification is evident in only the mid-parts of the posterolateral
arms. Ossification follows in the mid-parts of the anterolateral arms
and occurs last in the pterygoid pedicles. The palatines do not appear
until all three arms of the pterygoids are at least partly ossified.
Ossification proceeds rapidly from the maxillaries medially to the
unossified ethmoid, which is the last of the cranial bones to appear.
Initially it is extremely shallow; dorsally it is widely separated from
the nasals, and ventrally the posterior margin meets the anterior point
of the parasphenoid. In dorsal view, ossification proceeds anteriorly
between the nasals and posteriorly, ventral to the frontoparietals;
ventrally, ossification proceeds posteriorly dorsal to the parasphenoid.
The ventral arms of the squamosal and the supraoccipital region of the
exoccipital are the first occipital bones to appear. Ossification
follows in the regions of the semicircular canals and occipital
condyles. The dorsal end of the ventral arm of the squamosal and the
posterior arm of the squamosal ossify as a unit at the same time the
quadratojugal appears. Shortly thereafter the anterior arm of the
squamosal ossifies, the distal part of the columella appears, and the
anterior and lateral parts of the auditory region ossify.
The angular and dentary of the lower jaw appear concurrently with the
dentigerous bones. Initially, the angular is short and broad; the
articular surface is absent, and the anterior end is slightly overlapped
by the dentary. The mentomecklians do not ossify until approximately
the same time that the quadratojugal appears in the upper jaw.
_Comparative Osteology_
The genus _Smilisca_ is characterized by the following combination of
cranial osteological characters: (1) A large amount of bone is involved
in the skull and a minimal amount of cartilage and/or secondarily
ossified cartilage; co-ossification is absent. (2) The skulls are
uniformly broad with angular lateral margins, and truncate anteriorly.
(3) An internasal septum and quadratojugals are present. (4) A
well-developed squamosal minimally extends one-fourth the distance from
the dorsal end of the quadrate to the maxillary, and maximally is
separated from the maxillary by a suture. (5) The ethmoid is large; the
distance between the anterior end of the ethmoid and the anterior edge
of the premaxillary varies between 15 and 20 per cent of the total
length of the skull.
On the basis of cranial osteology two species-groups can be recognized
within the genus _Smilisca_. The _sordida_ group, comprising _S.
sordida_ and _puma_, is characterized by a broad skull in which the
lateral margins of the maxillaries are relatively straight anterior to
the orbit. The moderate-sized nasals are rounded anteriorly, and bear
relatively short, sometimes blunt, maxillary processes. The long axes of
the nasals are not parallel to the maxillaries. The ethmoid is
proportionately small in the _sordida_ group. The bony part of the
ethmoid terminates near the anterior edge of the orbits and does not
extend anteriorly between the nasals; the entire anterior margin of the
ethmoid is separated from the nasals by cartilage. The squamosals are
generally small. They are narrow in dorsal view, and minimally extend
one-fourth the distance from the dorsal end of the quadrate to the
maxillary, and maximally, two-thirds the distance. The tegmen tympani
are relatively small (Fig. 8).
[Illustration: FIG. 8. Dorsal views of the skulls of the species of
_Smilisca_: (A) _S. baudini_ (KU 68184); (B) _S. puma_ (KU 68636);
(C) _S. phaeota_ (KU 41090); (D) _S. sila_ (KU 80625); (E) _S.
cyanosticta_ (KU 55938), and (F) _S. sordida_ (KU 36765). x1.5.]
In contrast to the tendency for reduction of cranial parts in the
_sordida_ group, the _baudini_ group, constituted by _S. cyanosticta_,
_phaeota_, and _baudini_, is characterized by more ossification of the
cranial elements. The skull is broad; the lateral margins are less
angular and are gently curved, rather than straight as in the _sordida_
group. The nasals tend to be larger with the long axes parallel to the
maxillary. Anteriorly the nasals are pointed, and posteriorly they bear
long, delicate palatine processes extending to the maxillary. The
ethmoid is fully ossified, extends anteriorly between the nasals, and
laterally is separated by a suture from the nasals if the latter are
fully ossified. The squamosals are large, and wide in dorsal view. They
minimally extend one-fourth the distance from the dorsal end of the
quadrate to the maxillary, and maximally are sutured to the maxillary.
The tegmen tympani are massive.
_Smilisca sila_ is intermediate between the two species-groups
described. The skull is broad; the lateral margins are gently curved,
and have a pronounced angularity just anterior to the palatines which
results in a broad, truncate snout. The nasals are moderate in size;
because of the anterior angularity of the lateral margins, the long axes
of the nasals lie parallel to the maxillary. The nasals are only
slightly pointed anteriorly, and posteriorly they bear short, blunt
palatine processes and medial processes in contact with the lateral
corners of the ethmoid. The ethmoid is fully ossified, but does not
extend anteriorly between the nasals. The squamosals are moderate in
size and extend one-fourth the distance from the dorsal end of the
quadrate to the maxillary. The tegmen tympani are relatively large, but
proportionately short.
The cranial characters utilized in the analysis of species groups
(general shape, nature of the nasals, ethmoid, squamosals, and tegmen
tympani), together with other characters, such as the relative height
and shape of the prenasal processes, the extent of the internasal
septum, and the nature of the vomers, frontoparietals, maxillaries and
pterygoids are useful in distinguishing the various species (Table 4,
Fig. 8), as well as in establishing relationships within the
species-groups.
Within the _sordida_ group, _S. sordida_ and _S. puma_ can be
distinguished by the following characters: The bony part of the ethmoid
terminates posterior to the anterior edge of the orbit and is thus
widely separated from the nasals by cartilage in _S. puma_. In _S.
sordida_ the bony part of the ethmoid always terminates at a level equal
to, or slightly in front of the anterior edge of the orbit; therefore,
less cartilage exists between the ethmoid and nasals in _S. sordida_
than in _S. puma_. The width of the premaxillary comprises about 30 per
cent of the width of the skull in _S. sordida_ and 20 per cent in _S.
puma_. The proportion of the length of the skull anterior to the bony
part of the ethmoid in _S. sordida_ is approximately 21 per cent, as
compared with about 29 per cent in _S. puma_. The prenasal processes are
convex in _S. sordida_ and straight in _S. puma_.
The marked ontogenetic variation in _S. sordida_ is considered in more
detail in the account of that species, but it is pertinent to the
present discussion to note that with respect to some features of the
skull some young breeding specimens of _S. sordida_ are intermediate in
appearance between large females of _S. sordida_ and adults of _S.
puma_. In some breeding males (usually the smaller individuals) of _S.
sordida_ the bony part of the ethmoid terminates at the anterior edge of
the orbit and is widely separated from the nasals by cartilage. In small
individuals _S. sordida_, especially in males, and in adults of _S.
puma_ the tegmen tympani are relatively short, whereas in adult females
of _S. sordida_ these elements are long and slender. In the smaller
specimens of _S. sordida_ and in _S. puma_ the squamosal is small; it
extends only about one-fourth of the distance to the maxillary in the
smaller _S. sordida_ and about one-half the distance in _S. puma_. The
more massive squamosal in large adult females of _S. sordida_ extends at
least two-thirds of the distance to the maxillary.
Table 4.--Comparative Cranial Osteology of Smilisca.
===============+==============================+=======================
Character | _S. baudini_ | _S. cyanosticta_
---------------+------------------------------+-----------------------
| |
Alary Processes| Four times as high as | Three times as high
| lateral wing of premaxillary;| as lateral wing of
| anteriorly | premaxillary;
| convex. | anteriorly
| | convex.
| |
Nasals | Long, wide anteriorly, | Long, widest
| narrowing posteriorly; | posteriorly;
| attached to ethmoid. | attached to
| | ethmoid.
| |
| |
| |
Ethmoid | Long; entirely ossified; | Long, entirely
| smooth margins. | ossified;
| | smooth margins.
| |
Frontoparietal | Small, ovid fontanelle | Large fontanelle, two
| present or absent; | and one-half times as
| long, pointed postorbital | long as wide; narrow
| processes curving | supraorbital flanges
| along posterior | with irregular margins.
| border of orbit. |
| |
Squamosal | Large: anterior arm | Large; anterior arm
| in contact with maxillary. | in contact with
| | maxillary.
---------------+------------------------------+------------------------
TABLE 4 (Continued)
===============+=============================+=========================
Character | _S. phaeota_ | _S. puma_
---------------+-----------------------------+-------------------------
| |
Alary Processes| Two and one-half | Two times as high as
| times as high as lateral | lateral wing of
| wing of premaxillary; | premaxillary;
| anteriorly convex. | straight.
| |
| |
Nasals | Long, widest anteriorly | Short, narrow, not
| and posteriorly, | attached to ethmoid.
| bearing posteromedial |
| process; not attached |
| to ethmoid. |
| |
| |
Ethmoid | Long, entirely ossified; | Short, about two-thirds
| smooth margins. | ossified; irregular
| | margins.
| |
Frontoparietal | Fontanelle absent; | Keyhole-shaped fontanelle;
| large supraorbital | smooth margins;
| flanges having | flanges absent.
| straight edges and extending|
| posterolaterally. |
| |
| |
Squamosal | Large; anterior arm | Small; anterior arm
| extending 1/2-2/3 way | extending 1/2 way to
| to maxillary. | maxillary.
---------------+-----------------------------+--------------------------
TABLE 4 (Continued)
===============+===========================+============================
Character | _S. sila_ | _S. sordida_
---------------+---------------------------+----------------------------
| |
Alary Processes| One and one-half | Two and one-half
| times as high as lateral | times as high as lateral
| wing of premaxillary; | wing of premaxillary;
| straight. | slightly convex
| | anteriorly.
| |
Nasals | Short, wide, bearing | Moderately long narrowest
| small posteromedial | anteriorly and
| processes; not attached | posteriorly; not attached
| to ethmoid. | to ethmoid.
| |
| |
| |
Ethmoid | Moderately long; entirely | Short; one-half to entirely
| ossified; smooth | ossified; irregular
| margins. | margins.
| |
Frontoparietal | Large, ovoid fontanelle; | Large, elongate fontanelle;
| smooth margins; | smooth margins;
| flanges absent. | flanges absent.
| |
| |
| |
| |
Squamosal | Moderately large; anterior| Moderately small; anterior
| arm extending | arm extending
| 1/4 way to maxillary. | 1/4-2/3 way to maxillary.
---------------+---------------------------+----------------------------
Within the _baudini_ group, the skull of _S. cyanosticta_ is the most
generalized of the three species; the cranial characters are
intermediate between _S. phaeota_ and _S. baudini_. The lateral margins
of the skull in _S. cyanosticta_ are gently curved, and have an
angularity anterior to the palatine-maxillary suture; the anterior
margins are less angular in _S. phaeota_, which has a broader snout.
Posteriorly in _S. baudini_ the margins are slightly curved
medially, and the greatest width of the skull is between the
quadratojugal-maxillary sutures on either side of the skull. The
frontoparietals of _S. cyanosticta_ bear slightly irregular lateral
margins and a large fontanelle. There is a tendency for obliteration of
the fontanelle with increasing age in both _S. baudini_ and _S.
cyanosticta_; the lateral margins of the frontoparietals bear large
supraorbital flanges in both of these species. In _S. phaeota_ the
flanges are most prominent; they extend posterolaterally with straight
margins along two-thirds of the length of the orbit and terminate in
rather blunt points. The broad interorbital flanges result in a
relatively broad external interorbital distance. In _S. baudini_ the
flanges are curved posterolaterally around the orbit and terminate in
sharp, thin points. The tegmen tympani of all three species are massive.
In _S. cyanosticta_ the prooetics slope posteriorly, whereas they slope
anteriorly in _S. baudini_ and _S. phaeota_.
The skulls of _S. cyanosticta_ and _S. baudini_ are alike in certain
respects. The squamosals of both species are large and connected to the
maxillary by a bony connection; the squamosals of _S. phaeota_ are
large, but extend only two-thirds of the distance from the dorsal end of
the quadrate to the maxillary. In _S. baudini_ and _S. cyanosticta_ the
nasals are separated throughout their lengths from the ethmoid, whereas
the nasals of _S. phaeota_ are separated from the ethmoid by cartilage.
The latter separation is due to an incomplete ossification of the nasals
in _S. phaeota_. The bony part of each nasal is constricted in the
middle of the long axis of the bone, and the nasals are widest
anteriorly; posteriorly each nasal bears a medial process, which is
narrowly separated from the lateral edge of the ethmoid.
Table 5.--Variation in the Number of Teeth in the Species of
Smilisca. (All Are Males; N = Number of Jaws, or Twice the Number
of Individuals; Means Are Given in Parentheses After the Observed
Ranges.)
=================+====+==============+==============+===========
Species | N | Maxillary | Premaxillary | Vomerine
-----------------+----+--------------+--------------+-----------
_S. baudini_ | 20 | 49-65 (56.0) | 9-16 (13.6) | 5-9 (7.2)
_S. cyanosticta_ | 8 | 50-64 (57.9) | 10-12 (10.8) | 4-11 (7.1)
_S. phaeota_ | 20 | 50-68 (58.1) | 10-15 (12.1) | 5-9 (7.3)
_S. puma_ | 6 | 60-67 (63.6) | 11-13 (12.0) | 4-7 (5.3)
_S. sila_ | 8 | 48-60 (52.9) | 10-14 (11.3) | 5-7 (5.7)
_S. sordida_ | 12 | 39-55 (44.2) | 7-11 (9.3) | 4-6 (5.2)
-----------------+----+--------------+--------------+-----------
The teeth of all species of _Smilisca_ are spatulate and bifid. The
numbers of maxillary, premaxillary, and vomerine teeth are summarized in
Table 5. Smaller and presumably younger specimens of all species of
_Smilisca_ have fewer teeth than do larger specimens of the same
species. This correlation between size and number of teeth does not
exist as an interspecific trend within the genus; for example, the
smallest species in the genus, _S. puma_, has the highest number of
maxillary teeth. In small specimens of a given species wide gaps are
present between the maxillary teeth posteriorly; in large specimens the
gaps are filled by teeth, beginning anteriorly and progressing
posteriorly, until the maxillary dentition is continuous.
Musculature
No extensive study of the muscular system was undertaken, but certain
muscles know to be of taxonomic importance were studied.
_Jaw Musculature._--Starrett (1960) pointed out the unique jaw
musculature in _Smilisca_. In this genus M. depressor mandibulae
consists of two parts, one arising from the dorsal fascia and one from
the posterior arm of the squamosal. Two muscles arise from the anterior
arm of the squamosal and insert on the lateral face of the mandible. Of
these muscles, M. adductor mandibulae posterior subexternus lies medial
to the mandibular branch of the trigeminal nerve; the other, M. adductor
mandibulae externus superficialis, lies lateral to the same nerve (Fig.
9). In most other hylids the latter muscle is absent. No significant
variation in the position of the muscles was noted in the various
species of _Smilisca_, though M. adductor mandibulae originate somewhat
more anteriorly in _S. baudini_ and _S. cyanosticta_ than in the other
members of the genus, all of which have a shorter anterior arm of the
squamosal that does not reach the maxillary. The two separate parts of
M. depressor mandibulae are not so widely separated in members of the
_sordida_ group as in the _baudini_ group.