Osteology and skeletal development of Pyxicephalus adspersus (Anura: Ranidae: Raninae)

Despite the abundance and diversity of neobatrachians, relatively few descriptions exist of their ontogenesis and skeletal development. Herein, the adult and larval skeleton and the ontogenesis of the skeleton of the African frog, Pyxicephalus adspersus (Ranidae: Raninae), are described on the basis of cleared and double-stained, dry, and alcohol-preserved specimens. In P. adspersus, the first elements that ossify are the neural arches of the pre- and postsacral vertebrae (Gosner Stage 35), followed by the parasphenoid, frontoparietals, and exoccipitals (beginning at Stage 36). Major modifications of the chondrocranium begin at approximately Stage 40. The skull of the adult P. adspersus is exostosed and hyperossified, with many of the dermal bones of the cranium fused and highly ornamented. The osteology of the adult P. adspersus is compared to the skeletal morphologies of Conraua alleni (Raninae), which represents an African ranine for which osteological descriptions exist, and Ceratophrys cornuta (Leptodactylidae), which represents a hyperossified anuran with convergent morphology and behavior. The larval morphology and development of P. adspersus is compared to those of Rana pipiens and R. temporaria, which have been described in relative detail. The sequence of ossification of elements is compared with those of R. pipiens and R. temporaria. This study includes a discussion of the morphology of the elements forming the orbit, as well as a survey of the distribution of several characters related to dentary tusks of other Asian and African ranids. J. Morphol. 240:49-75, 1999. © 1999 Wiley-Liss, Inc.