The oldest therocephalians (Therapsida, Eutheriodontia) and the early diversification of Therapsida

The oldest records of mammal-like therapsids in Laurasia are from the Ocher Complex of Russia and the Xidagou Formation of China, whereas in Gondwana they are restricted to the Eodicynodon Assemblage Zone, Beaufort Group of the South African Karoo. This fauna, which is relatively depauperate when compared with younger assemblage zones from the Karoo, shows an amazing diversity of therapsids including: dinocephalians (already represented by the carnivorous anteosaurids and the herbivorous tapinocephalids), anomodonts (including dicynodonts), gorgonopsians, and therocephalians. The last group is represented by two specimens in this assemblage zone. This paper presents a full description of these therocephalians, which are assigned to the scylacosaurid species Glanosuchus macrops and Ictidosaurus angusticeps. We also discuss diversity trends of therocephalians and explore some hypotheses implicated by the diverse oldest record of therapsids, represented by five of the six major lineages of the group.