Taxonomic revision of the late Permian dicynodont genus <i>Endothiodon</i> (Therapsida, Anomodontia)

Abstract

The dicynodont genus Endothiodon, known for its unusual anatomy and possession of multiple tooth rows in some specimens, has a complex taxonomic history. We conducted a comprehensive review of 150 Endothiodon specimens from South Africa, Mozambique, Tanzania, Malawi, Zambia, Brazil and India to clarify taxonomy, diagnose species and understand relationships. Additionally, we analysed the biostratigraphic distribution of South African Endothiodon specimens, confined to the Endothiodon Assemblage Zone (AZ). Using 24 specimens, including four outgroup taxa, we created a character matrix with 22 new characters. Phylogenetic analysis revealed three clades: a basal clade representing the species Endothiodon mahalanobisi and two clades formed by the species Endothiodon tolani and Endothiodon bathystoma. Endothiodon bathystoma is diagnosed by a large pineal boss, E. tolani by an enlarged caniniform and a thin collar of bone around the pineal foramen, and E. mahalanobisi by an unornamented pineal foramen. 'Endothiodon uniseries' subsumes within E. bathystoma, suggesting that tooth row count must be used with caution as a character. Endothiodon mahalanobisi is exclusive to India, whereas all three of the valid Endothiodon species co-occur in Mozambique, whilst South African specimens exclusively represent E. bathystoma. Assuming contemporaneous deposition, a longitudinal gradient of Endothiodon diversity is evident, with East African basins harbouring the greatest diversity. This taxonomic revision clarifies the species diversity, intrageneric relationships and geographical distribution of Endothiodon. Our findings contribute to understanding the evolutionary history of these unique dicynodonts and emphasize the importance of considering both anatomical characteristics and geographical patterns in taxonomic investigations.