On the stratigraphic range of the dicynodont taxon Emydops (Therapsida: Anomodontia) in the Karoo Basin, South Africa

Angielczyk, Kenneth D.
Fröbisch, Jörg
Smith, Roger M. H.
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The dicynodont specimen SAM-PK-708 has been referred to the genera Pristerodon and Emydops by various authors, and was used to argue that the first appearance of Emydops was in the Tapinocephalus Assemblage Zone in the Karoo Basin of South Africa. However, the specimen never has been described in detail, and most discussions of its taxonomic affinities were based on limited data. Here we redescribe the specimen and compare it to several small dicynodont taxa from the Tapinocephalus and Pristerognathus assemblage zones. Although the specimen is poorly preserved, it possesses a unique combination of features that allows it to be assigned confidently to Emydops. The locality data associated with SAM-PK-708 are vague, but they allow the provenance of the specimen to be narrowed down to a relatively limited area southwest of the town of Beaufort West. Strata from the upper Tapinocephalus Assemblage Zone and the Pristerognathus Assemblage Zone crop out in this area, but we cannot state with certainty from which of these biostratigraphic divisions the specimen was collected. Nevertheless, SAM-PK-708 is an important datum because it demonstrates that the stratigraphic range of Emydops must be extended below its widely-accepted first appearance in the Tropidostoma Assemblage Zone. This range extension is significant because it implies that the divergence between the emydopid and dicynodontid lineages must have occurred no later than Pristerognathus Assemblage Zone times, and that most of the major lineages of Permian dicynodonts had emerged by a relatively early point in the history of the group.