A new species of<i>Emydops</i>(Synapsida, Anomodontia) and a discussion of dental variability and pathology in dicynodonts

ABSTRACT An enigmatic dicynodont specimen from Tweefontein in Graaff-Reinet, South Africa, represents a new species of the Middle to Late Permian genus Emydops, E. oweni. Taxonomic revision of the genus reveals that, of the thirteen previously described species, only E. arctatus is valid. The holotype of E. oweni, SAM-PK-3721 is unusual in that it bears two tusks on each side of the skull, a symmetrically developed double-tusked condition being a very rare if not unique case in the dicynodont fossil record. The possible pathological causes for this occurrence are discussed and the production of the supernumerary teeth by mutation is considered to be the most likely explanation. Phylogenetic analysis supports the sister-taxon relationship of the two species of Emydops and their position at the base of Emydopidae. Emydops oweni shares a number of derived characters with E. arctatus, including its small size, wide temporal region, prominent lateral dentary shelf, embayment on the medial surface of the palatal rim, and squared-off profile of occiput. In addition to its aberrant dentition, SAM-PK-3721 can be distinguished from the type species by a number of autapomorphies, including the absence of the small maxillary foramen lateral to the postcaniniform keel, the presence of a distinct ventrolaterally projecting pterygoid flange, and the diagnostic shape of the lateral dentary shelf. The identification of two additional tuskless specimens referable to the new species excludes the possibility that the autapomorphic characters are associated with the double-tusked condition, allowing us to conclude that E. oweni has both tusked and tuskless morphs.