Around 250 million years ago, our planet experienced what is probably the greatest extinction event for life forms, dubbed the Great Dying. Over 95 percent of marine species and 70 percent of terrestrial vertebrate lineages are estimated to have disappeared during this period, which marks the end of the Paleozoic era and the beginning of the Mesozoic.
It is believed that dinosaurs emerged and diversified a few million years after the extreme event.
A fossil discovered decades ago in Santa Cruz do Sul, in the Brazilian state of Rio Grande do Sul, and kept since then in the collection of the Federal University of Rio Grande do Sul (UFRGS), sheds new light on this moment in the evolution of dinosaurs.
The description of the fossil – which is thought to belong to a new species called Itaguyra occulta – was written by Brazilian and Argentinian paleontologists, based on two fossilized bones that were part of the animal’s pelvic girdle – an ilium and an ischium.
The study was published in Scientific Reports, one of Nature’s journals.
The scientists looked at the morphology of the bones and found that the creature was a member of the silesaurid group (of 
the reptile clade) and not a cynodont (the clade to which mammals belong).
The study shows that the fossil dates back some 237 million years – a period that has been little documented for silesaurs – and indicates that this group of animals had a continuous presence in the territory of present-day South America in the Triassic.
Based on the study’s conclusions, the scientists maintain that silesaurs are di-nosaurs, more precisely members of the ornithischian lineage, and not just their close relatives.
According to Voltaire Paes Neto, a researcher at Brazil’s National Museum of the Federal University of Rio de Janeiro and lead author of the study, “the discovery fills a critical time gap and supports the idea that silesaurs are not only close to dinosaurs, but may be the first representatives of ornithischians.”
“If this is confirmed, the Itaguyra occulta will become one of the oldest dinosaurs in the world,” the paleontologist pointed out.
“The continued presence of silesaurs in Brazil reinforces the role of the south of the country as a key territory for understanding the origin and diversification of dinosaurs,” said paleontologist Flávio A. Pretto, a researcher at the Federal University of Santa Maria (UFSM) and co-author of the study.
The new species is named after the origin of the find. “Itaguyra” combines the Tupi words “ita” (“stone”) and “guyra” (“bird”). “Occulta” refers to the fact that the remains were hidden among other materials for decades.
Source: Agência Brasil