The cranial osteology and hyolaryngeal apparatus of Rhinophrynus dorsalis (Anura: Rhinophrynidae) with comparisons to recent pipid frogs

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Abstract
The cranial osteology (including the hyolaryngeal apparatus) of Rhinophrynus dorsalis (Anura: Rhinophrynidae) is described from whole skeletons and serial cross sections. Some unique features of the extensively ossified skull include the enlarged and protracted olfactory region, for which the nasals form part of the septum nasi; the relatively short maxillaries and broad premaxillaries, and the immense quadratojugal; the extreme forward position of the quadrate; the lack of a firm articulation of the pterygoid and quadrate with the neurocranium and crista parotica; the quadrate lacking the distinct processes typical of other frogs; a single foramen for Nn. II–VII; a large, distinct operculum; and a bipartite hyale. Rhinophrynus shares other unusual cranial characteristics with the other pipoid frogs, Xenopus, Pipa, Hemipipa, and Hymenochirus. Among these features are the presence of a single frontoparietal in the adult, and the absence of parasphenoid alae, palatines, and mentomeckelian bones. Rhinophrynus differs from the pipids in the lack of a columella and a palatine process on the premaxilla, and in the possession of a quadratojugal, parahyoid bone, paired prevomers, olfactory eminence, massive quadrate that lacks distinguishable processes, a modified squamosal, and a bipartite hyale. Although the cranium of Rhinophrynus is distinctive, the evolutionary significance of its unusual features will remain obscure until comparable data are gathered from other closely related groups, the Discoglossoidea and the Pelobatoidea.