Fossil discovered in Brazil sheds light on the origin of dinosaurs
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 Friday (May 30) 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).
Silessaurids are considered dinosauromorphs, a broader group that includes dinosaurs and other lineages, but specialists still question whether they are dinosaurs or just a sister group of these more famous reptiles.
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 dinosaurs, more precisely 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 (UFRJ) and lead author of the study, “the discovery fills a critical time gap and s 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 director of the National Museum and co-author of the study, Alexandre Kellner, said that “the entire range of dinosaurs we’re familiar with is divided into two major lineages, the saurischians and the ornithischians, groups that have been recognized by science for more than a century and a half. However, how these lineages originated is still an enigma.”
Silesaurs include small, usually quadrupedal, omnivorous or herbivorous animals that lived in the late Triassic and have left fossil records in various regions of ancient Pangea, including present-day South America.
“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.
In addition to UFSM and the National Museum, scientists from UFRGS, the Federal University of Pampa (Unimpa), and the Argentine Museum of Natural Sciences took part in the study, with from the Rio de Janeiro State Research Foundation (Faperj) and the INCT-Paleovert project.
