The origin of dinosaurs in light of recent discoveries from Brazil

Abstract The origin of dinosaurs represents one of the most intriguing evolutionary events of the Mesozoic. Although dinosaurs ultimately came to dominate terrestrial ecosystems worldwide, their earliest evolutionary history unfolded within complex Triassic ecosystems dominated by synapsids and crocodile-line archosaurs. In this context, South America, particularly southern Brazil, preserves a critical fossil record documenting the emergence of dinosauromorphs and the initial radiation of Dinosauria. This contribution reviews recent discoveries of Triassic dinosauromorphs from the Santa Maria Supersequence of Rio Grande do Sul, Brazil, and discusses their implications for understanding early avemetatarsalian evolution, dinosaur origins, and the initial diversification of Dinosauria. The Brazilian record documents a nearly continuous presence of avemetatarsalians from the Middle (Ladinian) to Late Triassic (Norian), encompassing lagerpetids, silesaurids, herrerasaurids, theropods, and sauropodomorphs. These fossils provide key insights into major evolutionary transitions, including the rise and extinction of herrerasaurids as the earliest apex predatory dinosaurs, and the transformation of early sauropodomorphs from small-bodied carnivores into larger, herbivorous forms. Exceptional preservation in several Brazilian specimens, including articulated skulls and nearly complete skeletons, has substantially advanced our understanding of the anatomy, morphological disparity, and paleoecology during the early evolutionary history of dinosaurs. Despite remaining uncertainties in stratigraphic dating and phylogenetic relationships, the Triassic fossil record of southern Brazil stands as one of the most informative worldwide regarding the initial evolution of dinosauromorphs. Continued discoveries and refined stratigraphic frameworks promise to further clarify the tempo, mode, and ecological context of dinosaur origins.