New tetrapod remains help constrain the age of a peculiar assemblage, including early dinosaurs and pterosaur precursors, from the Upper Triassic of southern Brazil

The <i>Hyperodapedon</i> Assemblage Zone (AZ) is a key global marker of the Carnian stage in the Late Triassic. In the Candelária Sequence of Brazil (Rio Grande do Sul), it splits into the lower <i>Hyperodapedon</i> Acme Zone and the upper <i>Exaeretodon</i> Sub-AZ. Here we report new tetrapods from the previously overlooked lower exposures of the Niemeyer Complex (Agudo municipality). Intensive fieldwork yielded dozens of new specimens, including multiple hyperodapedontine rhynchosaur elements, as well as a partial skeleton referable to “<i>Hyperodapedon</i>” <i>sanjuanensis</i> via anatomical comparison and phylogenetic analysis, a lagerpetid, an early-diverging sauropodomorph, and a cynodont. This discovery provides evidence for the first definitive record of the <i>Hyperodapedon</i> Acme Zone in Agudo, with its fauna closely matching other late Carnian sites of southern Brazil, such as Buriol and Cerro da Alemoa, as well as correlative assemblages across southern Pangea. In contrast, the upper Niemeyer fauna is considered to be younger (latest Carnian–earliest Norian transition or early Norian) in age. Distinct lithologies, contrasting fossil assemblages, and the presence of index taxa support recognizing the lower and upper Niemeyer exposures as separate biozones. Our findings refine intercontinental correlations of Triassic tetrapods, enhance understanding of hyperodapedontine postcranial anatomy, and constrain the age of the lower beds of the Niemeyer Complex to the late Carnian.