New archosauromorph remains provide data on the age of a unique Late Triassic assemblage from southern Brazil

Abstract

The Santa Maria Supersequence, an important stratigraphic unit in the Paraná Basin, yielded a diverse range of Triassic tetrapod assemblages, providing valuable insights into the evolutionary history of southwestern Pangea. This study focuses on the Candelária Sequence of the Santa Maria Supersequence, which includes the Hyperodapedon Assemblage Zone (AZ) and the Riograndia AZ. The Hyperodapedon AZ is characterized by the presence of Hyperodapedon rhynchosaurs alongside a diverse array of other taxa, including dinosaurs, pseudosuchians, and cynodonts. In contrast, the Riograndia AZ preserves mostly small cynodonts, lepidosauromorphs, and sauropodomorph dinosaurs. Whereas biostratigraphic correlations between several localities of the Candelária Sequence have been firmly established, certain sites, like the Niemeyer complex in the Agudo municipality of southern Brazil, present challenges because of their unusual assemblage composition, which result in ambiguous depositional ages. Despite yielding thousands of fossil specimens, the Niemeyer complex lacks index fossils typical of the known Brazilian AZs, making reliable correlation with other sites challenging. This study presents and describes new archosauromorph specimens discovered at the upper portion of the Niemeyer complex. The new materials include a rhynchosaur, a saurischian dinosaur, and a possible silesaurid, which represent the first record of these groups for the site. A phylogenetic analysis of the rhynchosaur material provides insights into its taxonomic affinities, offering valuable data for biostratigraphic comparisons. The new data reinforces an age (early Norian?) that is younger than that of the typical outcrops assigned to the Hyperodapedon AZ. Furthermore, these new specimens contribute to the unique assemblage of the Niemeyer complex, shedding light on its significance within the context of the Santa Maria Supersequence and the broader landscape of southern Brazil during the Triassic Period.