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

Long before dinosaurs ruled the continents and modern crocodiles first appeared, their ancestors were already going through a decisive phase in their evolutionary history. It was in this ancient world, shortly after the greatest mass extinction in Earth’s history that a new species of fossil reptile discovered in the interior of Brazil’s Rio Grande do Sul state.

Named Silescelida acristata, the species lived about 240 million years ago, during the Middle Triassic Period. The fossil was found in Dona Francisca, in central Rio Grande do Sul, in rocks that are part of the UNESCO Quarta Colônia Geopark.

The discovery helps fill an important gap in our understanding of the evolution of archosauriformes, a group of reptiles that gave rise to the archosaurs. Archosaurs, in turn, are the lineage that encompasses two of the best-known groups of terrestrial vertebrates: crocodiles and dinosaurs, including birds.

The study was conducted by researchers from the Quarta Colônia Center for Paleontological Research at the Federal University of Santa Maria, CAPPA/UFSM, in collaboration with researchers from the Federal University of Rio Grande do Sul (UFRGS) and the Pontifical Catholic University of Rio Grande do Sul (PUCRS), and was published in the scientific journal Scientific Reports.

A small animal in a world under reconstruction

When Silescelida acristata lived, terrestrial ecosystems were still recovering from the Permian–Triassic extinction event, which occurred about 252 million years ago. This event wiped out much of the life on the planet and paved the way for the diversification of new groups of animals.

It was against this backdrop of ecological recovery that different lineages of reptiles began to take on new roles in terrestrial environments. Among them were the archosauriforms, which underwent extensive diversification during the Triassic. Silescelida acristata was a relatively small, slender animal........

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