A Synopsis of Neotropical Hylid Frogs, Genus Osteocephalus

by Linda Trueb; William Edward Duellman

Fig. 5.	Palmar views of hands of males of Osteocephalus:
	a. O. buckleyi, KU 109506; b. O. leprieurii, KU 126627; c. O. pearsoni, MCZ 15565; d. O. taurinus, KU 126653; e. O. verrucigerus, KU 123177. ×4.

Fig. 6.	Skulls of two species of Osteocephalus:
	a and b. O. leprieurii, KU 125961; c and d. O. pearsoni, UMMZ 67465. ×3.

The genus is characterized by well-developed dermal roofing bones and an unusually large exposure of the sphenethmoid dorsally ([Fig. 6]). The conformation of the sphenethmoid exposed dorsally is determined by the marginal positions of the adjacent, overlapping elements—the nasals and frontoparietals. Medially the nasals overlap the lateral margins of the sphenethmoid. Anteromedially, the nasals converge in leprieurii and taurinus, are narrowly separated in buckleyi and pearsoni, or are more widely separated in verrucigerus. In all species the nasals terminate at the anterodorsal corner of the orbit. The frontoparietals of buckleyi, leprieurii, and taurinus have an anterolateral extension, which marginally overlaps the dorsolateral edge of the sphenethmoid and articulates with the posterodorsal corner of the nasal in buckleyi and taurinus; the bones are narrowly separated in leprieurii. The frontoparietals of pearsoni and verrucigerus have more extensive median ossification and less extensive anterolateral ossification. Thus, in those species the posteromedian portion of the sphenethmoid is obscured, and the lateral margins are partly exposed. The frontoparietal fontanelle is completely covered in all species, except buckleyi and leprieurii, in which an irregular, median separation of the frontoparietals exposes a small portion of the fontanelle. The posterolateral margins of the frontoparietals lie medial to the epiotic eminences.

Dermal ornamentation, involving the nasals, frontoparietals, and sphenethmoid, occurs in taurinus and, to a limited extent, in pearsoni. In the latter species marginal portions of the frontoparietals, the dorsal surfaces of the nasals, and the posteromedial part of the exposed sphenethmoid are slightly exostosed, resulting in an open, reticulate pattern of dermal sculpturing of exceedingly low relief ([Fig. 6c]). Osteocephalus taurinus is characterized by casquing, co-ossification, and a rather intricate pattern of dermal sculpturing, which was described in detail and illustrated by Trueb (1970a).

The squamosals of all species are moderately large structures having otic plates that overlie the lateral portion of the cristae paroticae. The posterior rami are short; the zygomatic rami of all species, except taurinus, extend slightly more than one-half of the distance to the maxillary. In taurinus the zygomatic ramus extends nearly to, or articulates with, the maxillary.

The maxillary arches are complete and relatively robust. The alary processes of the premaxillaries are vertically oriented in leprieurii, pearsoni, and taurinus and very slightly inclined posteriorly in buckleyi and verrucigerus. The maxillaries are uniformly characterized by the absence of postorbital processes and by the presence of preorbital processes that articulate with the maxillary processes of the nasals. The partes facialae of the maxillaries are moderately developed in all species, except taurinus, in which the pars fascialis tends to articulate with the lateral margin of the nasal in well-ossified individuals. The partes palatinae are poorly developed in all species, except buckleyi, in which the pars palatina of the premaxillary is moderately robust.

The pterygoids are uniformly tri-radiate structures. The anterior rami terminate at about the mid-level of the orbit, and the medial rami articulate firmly with the anterolateral corner of the otic capsule. The palatines are well-developed elements bearing ventral ridges; the ridges are somewhat irregular in buckleyi, taurinus, and verrucigerus but smooth in leprieurii and pearsoni. The parasphenoids are large elements characterized by acuminate cultriform processes and posterolaterally inclined alary processes. The basal areas of the cultriform processes bear small odontoid protuberances in buckleyi, taurinus, and verrucigerus, whereas they are smooth in leprieurii and pearsoni. The prevomers are remarkably uniform, moderately well-developed structures. In each species the anterior ramus lies adjacent to the premaxillary, and the lateral wings form the anterior, medial, and posteromedial margins of the internal nares. The dentigerous processes are characteristically large and angular and bear numerous teeth. The sphenethmoid and otoccipitals are well ossified; a dermal sphenethmoid is present only in taurinus.