A reptile that lived before the dinosaurs appeared has been discovered in Brazil

The discovery was made possible by a fossil fragment that had been thought to be lost for over 20 years. It still bore its museum accession number, which made it possible to determine exactly where the remaining bones had been found.

The ancient reptile was not a direct ancestor of dinosaurs or crocodiles. However, it belonged to one of the early branches of the archosauriforms — a large group from which the archosaurs later emerged, including dinosaurs, birds and crocodiles.

Details

The fossils were discovered near the municipality of Dona Francisca in the Brazilian state of Rio Grande do Sul. They come from Middle Triassic rocks within the Quarta Colônia Geopark, which is part of the UNESCO Global Geoparks Network.

Only part of the skeleton has been preserved. The palaeontologists had at their disposal the left scapula, part of the right side of the pelvis and an almost complete left femur, approximately 17 centimetres long. All the elements were found together and matched each other in size, so the researchers concluded that they belonged to a single animal.

According to the reconstruction, Silescelida acristata was a relatively small and slender reptile that moved on four legs. In size, it may have been comparable to a small alligator. The animal probably hunted smaller prey, although this conclusion is based on comparisons with related species: the skull and teeth of the new reptile have not been preserved.

The femur proved to be particularly significant. Its structure indicates that the animal’s legs were not positioned strictly at the sides of the body, as in many early reptiles, but were partially directed downwards. This semi-erect limb posture may have made locomotion more efficient.

The authors compared the bones with those of other Triassic reptiles and included the new species in a large database containing 287 animal groups and 919 anatomical characters. Several analyses consistently placed *Silescelida acristata* amongst the early eucrocopods — archosaur-like reptiles whose structure was similar to the general body plan of archosaurs.

The exact position of the species on the evolutionary tree remains a matter of debate. In some analyses, it was placed within the family Euparkeriidae, whilst in others it was placed alongside it. The researchers therefore refer to the animal only as a possible member of this family.

A fossil lost for 20 years

The story of its discovery has spanned decades. A section of the femur, on which the specimen’s museum number was inscribed, was accidentally lost. Without it, palaeontologists were unable to confirm the location and circumstances of the find, making it impossible to fully describe the animal.

The fragment was rediscovered whilst examining the collection at the Pontifical Catholic University of Rio Grande do Sul. Following this, the scientists were able to piece the fossil back together, establish its origin and describe a new genus and species.

This story is reflected in the animal’s name. The word Silescelida is derived from the Latin word meaning ‘silence’ and the Greek word for ‘hind leg’. The specific epithet ‘acristata’ translates as ‘without a crest’ and refers to the absence of a characteristic bony protrusion on the thigh.

Why this is important

The new species lived during a period when terrestrial ecosystems were still recovering from the Permian mass extinction, which occurred around 252 million years ago. This was the largest catastrophe of its kind in Earth’s history: it freed up numerous ecological niches and altered the subsequent evolution of animals.

During the Triassic, archosaur-like creatures rapidly diversified and developed new body forms. Later, one branch of the archosaurs gave rise to crocodiles, whilst another led to pterosaurs, dinosaurs and modern birds.

Silescelida acristata helps us to glimpse an earlier stage in this history, when reptiles closely related to archosaurs still differed in their diverse body structures and modes of locomotion. The discovery also suggests that such animals were more widespread than the known fossil record had previously indicated.

However, it is too early to draw definitive conclusions. The skeleton consists of only a few bones, and the position of the new species varies depending on the analytical approach. Therefore, the discovery refines our understanding of the evolution of archosauriforms, but does not reveal a specific common ancestor of dinosaurs and crocodiles.

Background

Presumed members of the family Euparkeriidae were previously known mainly from finds in Africa, Asia and Europe. The new species is the first early eucrocopod discovered in Triassic deposits in Brazil, and the first possible member of the Euparkeriidae in South America.

Rio Grande do Sul is considered one of the most important regions for the study of the Triassic period. The local strata contain the remains of early dinosaurs, their relatives and predatory reptiles that inhabited the Earth before the dawn of the Age of Dinosaurs.

Source

The study was conducted by Maurício S. Garcia, Gabriela M. Serqueira, Francesco Battista and their colleagues. The paper ,‘A new eucrocopodan archosauriform from the Middle Triassic of southern Brazil and the phylogeny of Euparkeriidae’, was published in the journal Scientific Reports in 2026.