Old fossil findings in the Upper Triassic rocks of southern Brazil improve diversity of traversodontid cynodonts (Therapsida, Cynodontia)

In this contribution we describe a new genus and species of gomphodontosuchine cynodont from the Late Triassic Hyperodapedon Assemblage Zone (AZ) of the Santa Maria Supersequence of southern Brazil, based on material collected 20 years ago. The new taxon, Santagnathus mariensis gen. et sp. nov., is based on numerous cranial and postcranial remains, which altogether provide data on several parts of the skeleton. Santagnathus mariensis is closely related to Siriusgnathus niemeyerorum and Exaeretodon spp. and expands the knowledge about gomphodontosuchine cynodonts. Morphologically, the new species has a skull bauplan particularly similar to S. niemeyerorum and E. riograndensis, differing from them by a unique combination of traits such as three upper incisors, the absence of a descending process in the jugal, a more posterior position of the postorbital bar and a preorbital region larger than the temporal one. The new traversodontid was found associated with the rhynchosaur Hyperodapedon sp., corroborating the assignment of the cynodont fossils to the Hyperodapedon AZ. We also provide comments on the status of the Argentine traversodontid cynodont Proexaeretodon vincei, typically considered a junior synonym of Exaeretodon argentinus, and here accepted as a valid taxon.

Automated summary

In this paper, a new genus and species of gomphodontosuchine cynodont from the Late Triassic Hyperodapedon Assemblage Zone of southern Brazil is described. The new taxon, Santagnathus mariensis, is closely related to Siriusgnathus niemeyerorum and Exaeretodon spp. It expands our knowledge about gomphodontosuchine cynodonts and exhibits a skull bauplan similar to S. niemeyerorum and E. riograndensis, but with unique traits. The new species was found associated with the rhynchosaur Hyperodapedon sp., confirming its attribution to the Hyperodapedon Assemblage Zone.