AbstractNew specimens of the oldest gorgonopsian taxon Eriphostoma microdon from the Pristerognathus Assemblage Zone (AZ) of South Africa significantly improve our understanding of the anatomy of this taxon. The new specimens consist of nearly complete skulls and lower jaws and allow for a more complete diagnosis of Eriphostoma than was possible based on the poorly preserved holotype. In addition to the characteristic palatal dentition and delta‐shaped palatine bosses previously recognized for Eriphostoma, this taxon can be diagnosed by the presence of three close‐packed upper postcanines occupying an indented margin of the maxilla, a large, tetragonal‐to‐rounded preparietal bone, and large, paired interorbital depressions expanding outwards in front of the pineal boss. The revised diagnosis permits Eoarctops vanderbyli, Galesuchus gracilis, and Scylacognathus parvus to be synonymized with Eriphostoma microdon, as previously suspected. Among gorgonopsians, Eriphostoma is most similar to Aelurosaurus and Gorgonops, although these similarities are likely plesiomorphic for Gorgonopsia. Eriphostoma ranges from the Tapinocephalus AZ (where it is the only valid gorgonopsian known from the Karoo Basin) through the Pristerognathus AZ (where it co‐occurs with Gorgonops).