New proterochampsid remains from the Middle Triassic of Brazil enhance the group's diversity during its origins

Proterochampsidae is a clade of archosauriform reptiles that lived during the Triassic Period, with notable fossil records in South America. Among these, Ladinian deposits in Brazil have yielded the oldest proterochampsids worldwide, offering insights into the origins of the group. However, their record from this interval remains scarce, with only two species previously described: Pinheirochampsa rodriguesi and Retymaijychampsa beckerorum. Here, I report the first proterochampsid specimen from the Posto site (Pinheiros-Chiniquá Sequence; Dinodontosaurus Assemblage Zone) in Dona Francisca, Rio Grande do Sul. The new specimen, CAPPA/UFSM 0459, comprises the anterior tip of a rostrum, identified as a proterochampsid based on its dorsoventrally flattened premaxilla with a dorsally facing external naris and anterior narial fossa. Despite its fragmentary nature, CAPPA/UFSM 0459 represents the first non-archosaur archosauriform identified at the Posto site, suggesting a small carnivorous member of this local fauna. Comparisons indicate it is unlikely to belong to any previously described species. This finding highlights the diversity and ecological significance of early proterochampsids within Middle Triassic ecosystems dominated by therapsids, pseudosuchians, and early dinosauromorphs.