A second burnetiamorph therapsid from the Permian Teekloof Formation of South Africa and its associated fauna

ABSTRACT

A new burnetiamorph therapsid, Lophorhinus willodenensis, gen. et sp. nov., is described on the basis of a partial skull from the Permian Teekloof Formation (Beaufort Group) of the Beaufort West District, Western Cape Province, South Africa. Although similar to the coeval burnetiamorph Lobalopex, Lophorhinus is autapomorphic in its possession of a semicircular median nasal crest formed by unfused nasals, doubled lacrimal foramina, an ossified sphenethmoid, and a mesiodistally compressed first premaxillary tooth. New morphological data provided by Lophorhinus permit the recognition of several character states that have been difficult to evaluate in other burnetiamorph taxa, including a (1) short dorsal process of the premaxilla, (2) contribution of the frontal to the upper orbital margin, and (3) lack of a significant contribution of the prefrontal to the supraorbital boss. An updated cladistic analysis of twelve biarmosuchians suggests that Lophorhinus is the sister taxon to Lobalopex + Burnetiidae. However, the precise relationships among Lemurosaurus, Lobalopex, and Lophorhinus are unresolved in the strict consensus of 25 primary trees. The discovery of Lophorhinus in the Tropidostoma Assemblage Zone (AZ) demonstrates that multiple burnetiamorph taxa co-existed in southern Gondwana during Middle and Late Permian times. Systematic collecting from the Tropidostoma AZ suggests that carnivorous burnetiamorphs, gorgonopsians, and therocephalians are exceedingly rare components of the tetrapod fauna, with herbivorous dicynodonts dominating the fossil record (121/126 specimens collected). Field collections of tetrapods from the Tropidostoma AZ are most similar in their composition to those described from the stratigraphically higher Dicynodon AZ, implying relatively stable tetrapod community structure in southern Pangea for the final 10 million years of the Permian.