Mandibular anatomy of a new specimen of a prozostrodontian cynodont (Eucynodontia: Probainognathia) from the Upper Triassic of Brazil.

Prozostrodontia is a clade of probainognathian cynodonts that exhibit several morphological innovations later inherited by mammals. The earliest representatives of this group have been found in the Upper Triassic deposits of southern Brazil. In this study, we report the discovery of a probainognathian cynodont from the Buriol site (São João do Polêsine, Rio Grande do Sul, Brazil), Hyperodapedon Assemblage Zone (Late Triassic). This site is well-known for its record of archosauromorphs. The specimen consists of a right dentary preserving one incisor, one canine, and seven postcanine teeth. Its morphology suggests a close relationship with early prozostrodonts, particularly Prozostrodon brasiliensis. Key traits supporting this affinity include the non-fused symphysis, a thin groove for the dental lamina, and distal postcanine with a central cusp slightly distally oriented and showing a lingual cingulum. Unusually, the incisor displays serrations on its mesial and distal margins and the canine on its distal margin, a rare feature among probainognathians. However, the fragmentary nature of the specimen and the limited comparative data preclude a more specific taxonomic assignment. Nevertheless, it contributes to our understanding of the morphological diversity within Carnian probainognathians. It also expands the known fauna of the Buriol site, which now includes cynodonts alongside rhynchosaurs, aetosaurs, early dinosaurs, and lagerpetids.