Named Silescelida acristata — roughly "silent leg, without a crest" — the small reptile lived about 240 million years ago in the Middle Triassic, a world still recovering from the Permian–Triassic extinction that wiped out much of life 252 million years ago.
The fossil was found in Dona Francisca, in central Rio Grande do Sul, in rocks belonging to the UNESCO Quarta Colônia Geopark. Researchers from the Quarta Colônia Center for Paleontological Research at the Federal University of Santa Maria (CAPPA/UFSM), together with colleagues from UFRGS and PUCRS, described the species in the journal Scientific Reports.
About the size of a small alligator, Silescelida acristata was a slender, four-legged predator that likely fed on smaller animals. Its most telling feature is its femur: the legs were held in a more semi-erect position than those of earlier reptiles, reducing drag and enabling more efficient locomotion — an anatomical experiment that would prove fundamental to the later success of archosaurs, the lineage that gave rise to crocodiles, dinosaurs and birds.
Phylogenetic analyses link the new species to the Euparkeriidae, a rare and poorly understood group of archosauriforms previously known mainly from Africa, Asia and Europe. Its presence in South America significantly expands the known distribution of these reptiles and reinforces the continent's role in the early diversification of dinosaurs and crocodiles.
The discovery also has an unusual backstory: part of the fossil — the fragment carrying essential provenance information — was lost for more than two decades, rediscovered only in 2022 during a technical visit to the scientific collection at PUCRS. "Silence" in the name refers to the forgotten fragment; "leg" to the limb bones that made identification possible, and acristata ("without a crest") to the missing trochanter that sets the animal apart from nearly all close relatives.
