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 | S. phaeota | S. puma | S. sila | S. sordida |
| Alary Processes | Four times as high as lateral wing of premaxillary; anteriorly convex. | Three times as high as lateral wing of premaxillary; anteriorly convex. | Two and one-half times as high as lateral wing of premaxillary; anteriorly convex. | Two times as high as lateral wing of premaxillary; straight. | One and one-half times as high as lateral wing of premaxillary; straight. | Two and one-half times as high as lateral wing of premaxillary; slightly convex anteriorly. |
| Nasals | Long, wide anteriorly, narrowing posteriorly; attached to ethmoid. | Long, widest posteriorly; attached to ethmoid. | Long, widest anteriorly and posteriorly, bearing posteromedial process; not attached to ethmoid. | Short, narrow, not attached to ethmoid. | Short, wide, bearing small posteromedial processes; not attached to ethmoid. | Moderately long narrowest anteriorly and posteriorly; not attached to ethmoid. |
| Ethmoid | Long; entirely ossified; smooth margins. | Long, entirely ossified; smooth margins. | Long, entirely ossified; smooth margins. | Short, about two-thirds ossified; irregular margins. | Moderately long; entirely ossified; smooth margins | Short; one-half to entirely ossified; irregular margins. |
| Frontoparietal | Small, ovid fontanelle present or absent; long, pointed postorbital processes curving along posterior border of orbit. | Large fontanelle, two and one-half times as long as wide; narrow supraorbital flanges with irregular margins. | Fontanelle absent; large supraorbital flanges having straight edges and extending posterolaterally. | Keyhole-shaped fontanelle; smooth margins; flanges absent. | Large, ovoid fontanelle; smooth margins; flanges absent. | Large, elongate fontanelle; smooth margins; flanges absent. |
| Squamosal | Large: anterior arm in contact with maxillary. | Large; anterior arm in contact with maxillary. | Large; anterior arm extending 1/2-2/3 way to maxillary. | Small; anterior arm extending 1/2 way to maxillary. | Moderately large; anteriorarm extending 1/4 way to maxillary. | Moderately small; anterior arm extending 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 proötics 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) | ||