Widespread distribution of large silesaurids evidenced by a new record from the Middle Triassic of southwest Gondwana

Silesaurids are Triassic dinosauromorphs with debated phylogenetic affinities, recently recovered as a paraphyletic assemblage along the stem leading to ornithischian dinosaurs. Despite their uncertain relationships, silesaurids provide key insights into early dinosaur evolution. Most specimens are fragmentary and small, limiting understanding of their body size and ecological roles. Here, I describe an almost complete femur from the Middle Triassic of southern Brazil, representing the largest silesaurid known from South America and one of the largest worldwide, with an estimated femoral length of 227-269 mm. The new specimen demonstrates that silesaurids attained large body sizes in southwestern Gondwana, suggesting they functioned as primary to secondary herbivorous or omnivorous consumers within Middle Triassic terrestrial ecosystems. Comparison with coeval taxa indicates that these large forms were unlikely prey for most contemporaneous predators once fully grown. The discovery also highlights the widespread geographic distribution and temporal persistence of large silesaurids across Pangea, despite faunal turnovers and environmental events such as the Carnian Pluvial Episode.