===============+=======================+========================+
Character | _H. microcephala_ | _H. robertmertensi_ |
---------------+-----------------------+------------------------+
Frontoparietal | Minimally ossified | Ossification extensive |
| with large fontanelle | anteriorly with narrow |
| extending from | medial separation; |
| sphenethmoid to | fontanelle largest in |
| occipital ridge. | parietal region. |
| | |
| | |
Nasals | Moderately long and | Moderate in size; |
| slender; arcuate in | slightly wider |
| dorsal view. | anteriorly than |
| | posteriorly in dorsal |
| | view. |
| | |
Sphenethmoid | Extremely short in | Moderately short in |
| dorsal view. | dorsal view. |
| | |
| | |
| | |
Columella | Distal and greatly | Distal and slightly |
| expanded. | expanded or not. |
---------------+-----------------------+------------------------+
Table 4. (Continued)
===============+========================+========================
Character | _H. phlebodes_ | _H. sartori_
---------------+------------------------+------------------------
Frontoparietal | Ossification extensive | Ossification moderately
| anteriorly with narrow | extensive anteriorly;
| medial separation; | medial separation of
| fontanelle largest in | about uniform width
| parietal region. | throughout length of
| | fontanelle.
| |
Nasals | Moderate in size; | Long and broad;
| slightly wider | arcuate in dorsal
| anteriorly than | view.
| posteriorly in dorsal |
| view. |
| |
Sphenethmoid | Moderately short in | Moderately short in
| dorsal view. | dorsal view; ossified
| | anteriorly between
| | nasals.
| |
Columella | Distal and not | Distal and not
| expanded. | expanded.
---------------+------------------------+------------------------
[Illustration: Fig. 5. Dorsal views of the skulls of (a) _Hyla m.
microcephala_ (KU 68293) and (b) _H. sartori_ (UMMZ S-2677).
Both x 12.]
[Illustration: Fig. 6. Dorsal views of skulls of (a) _Hyla phlebodes_
(KU 68303) and (b) _H. robertmertensi_ (KU 59917). Both x 12.]
Despite the great reduction in the ossification of the cranial
elements, certain apparently consistent differences exist between the
species seem to be consistent. The most notable differences are:
1) amount of ossification of the frontoparietals and consequent shape
and size of the frontoparietal fontanelle, 2) shape of the nasals,
3) shape and extent of the sphenethmoid, and 4) shape of the columella
(Table 4, Figs. 5-6). On the basis of these characters, _Hyla
microcephala_ can be set apart from the other species and characterized
as having a poorly ossified frontoparietal and correspondingly large
frontoparietal fontanelle; long, slender, arcuate nasals; extremely
short sphenethmoid; and expanded distal end of the columella. The other
species in the group (_phlebodes_, _robertmertensi_, and _sartori_)
have more ossification of the frontoparietals, broader nasals, only a
moderately short sphenethmoid, and an unexpanded distal end of the
columella. Among these three species, the skulls of _phlebodes_ and
_robertmertensi_ are most nearly alike, whereas the skull of _sartori_
differs by having a differently shaped frontoparietal fontanelle,
broader nasals, and an ossified anterior extension of the sphenethmoid
between the nasals (compare Fig. 5b with Fig. 6 a-b).
Although all skulls examined belong to breeding adults, the extent of
the ossification of the frontoparietals and the resulting shape of the
frontoparietal fontanelle might be correlated with the age of the frog.
Nevertheless, in the 24 skulls of _Hyla microcephala_ examined, the
frontoparietals are less extensively ossified than in the skulls of the
other species. The trivial differences among the other three species
certainly are suggestive of close relationship, but on the basis of
present knowledge of the evolutionary trends in hylid cranial
osteology, the differences offer little evidence for determining
phylogenetic lineage.