A fossil lost for 20 years just rewrote the map of dinosaur ancestry

Twenty years ago, a fossil named Silescelida acristata was lost, only to be rediscovered and rewrite our understanding of dinosaur ancestry. This small, four-legged animal lived around 240 million years ago during the Middle Triassic Period in Brazil's Rio Grande do Sul state. The discovery sheds light on the evolution of archosauriforms, a group of reptiles that gave rise to dinosaurs, crocodiles, and birds.

The fossil, found in rocks part of the UNESCO Quarta Colônia Geopark, preserved parts of the limbs, offering insights into the animal's locomotion and evolutionary relationships. Its semi-erect legs, lower on the body, allowed for more efficient movement, a trait that would later be crucial for the success of archosaurs. Phylogenetic analyses suggest that Silescelida acristata may be related to the Euparkeriidae, a rare group of archosauriforms primarily found in Africa, Asia, and Europe.

The presence of this related fossil in South America suggests these reptiles were more widely distributed during the Triassic than previously thought. The rediscovery of Silescelida acristata also highlights the importance of South America in the study of the origin and diversification of major terrestrial vertebrate groups. This find broadens our understanding of the complex and diverse evolutionary history of archosauriforms, indicating a broader role for South America in their early diversification.