Abstract

A new genus and species of biarmosuchian therapsid, Herpetoskylax hopsoni, is described on the basis of a well preserved skull and lower jaws from the rocks of the Cistecephalus Assemblage Zone (Upper Permian) of the Beaufort West District of South Africa. Autapomorphies of Herpetoskylax include the lack of a distinct fossa on the posterior surface of the squamosal, the degree to which the zygomatic arch appears elevated in lateral view, and the large size of the quadratojugal foramen and post-temporal fenestrae.
We review recent work on biarmosuchian systematics and taxonomy. Rubidgina angusticeps is found to be based on an undiagnostic holotype and declared a nomen dubium. A specimen previously referred to Rubidgina is instead referable to Herpetoskylax. We re-evaluate previously proposed biarmosuchian synapomorphies and provide a revised cladistic analysis of the group. Our analysis includes 13 ingroup taxa (four dinocephalians, two anomodonts, seven biarmosuchians) and 56 characters of the skull, lower jaw, and dentition. A strict consensus of nine minimum length trees suggests that Dinocephalia, Anomodontia, and Biarmosuchia (minus Biarmosuchus) are monophyletic taxa. Relationships among these clades are incompletely resolved, but in most trees biarmosuchians form a clade that is the sister taxon to Anomodontia, with Dinocephalia positioned as the most primitive therapsid clade. Within Biarmosuchia, Hipposaurus and (variably) Biarmosuchus represent the two most primitive forms. Herpetoskylax, along with Lycaenodon and Ictidorhinus, is positioned between these two taxa and the derived biarmosuchian subclade, Burnetiamorpha.