Reinterpretation of a larval dissorophoid amphibian from the Lower Permian of Texas

Abstract

Restudy of the only indisputable larval temnospondyl from the Lower Permian (Arroyo Formation: Clear Fork Group) of North America has revealed the presence of a narial flange, which supports its assignment to the superfamily Dissorophoidea. Two families of dissorophoids, the Trematopsidae and Dissorophidae, are recognized in the Pennsylvanian and Permian of North America. Contrary to the initial description, the elongated external naris of the larva differs significantly from that of trematopsids, and it is reinterpreted as a homoplastic character. No definitive characters of trematopsids can be found in the larva, and it is, therefore, excluded from this family. In the absence of a diagnosis of the Dissorophidae, it is not possible to assign this extremely immature specimen to that family. The unique configuration of the external naris excludes the larva from any known genus of dissorophid, but only on the assumption that an adult would have a similarly shaped external naris. Future studies of the Dissorophidae using modern systematic techniques could resolve the taxonomic position of the larva. At present, the only supportable conclusion is that the larva is a dissorophoid.