A Rare Triassic Fossil Found in Brazil Could Shed Light on the Origin of Dinosaurs

In Paraíso do Sul in southern Brazil, scientists discovered a fossil of a dog-sized reptile dating back to 237 million years ago. The creature, a newly described species named Gondwanax paraisensis, could shed light on the origin of the oldest dinosaurs, though paleontologists still have questions about its spot on the evolutionary tree.

The animal had four legs and was 39 inches in length, with a long tail, according to a paper published this fall in the journal Gondwana Research. It belongs to an extinct group of reptiles called silesaurids. These lived during the Triassic period and are typically not considered true dinosaurs. Instead, they’re usually viewed as close relatives. The new fossil found in Brazil, however, could change that.

“The most important part of this finding is its age,” says Rodrigo Temp Müller, sole author of the study and a paleontologist at the Federal University of Santa Maria in Brazil, to Reuters’ Sergio Queiroz and Diego Vara. “Because it’s so old, it gives us clues as to how dinosaurs came to be.”

Paleontologists debate where silesaurids fall in dinosaur evolution: Were they true dinosaurs? Or extremely close precursors? Some paleontologists have asserted silesaurids are a sister group to dinosaurs—descendants of the same common ancestor, but separate.

Others argue that silesaurids were grouped together because they contained some of the anatomical features of later ornithischians—herbivorous dinosaurs including Stegosaurus and Triceratops that had a pelvic structure similar to that of birds. Some researchers suggest silesaurids are a sister group of the ornithischians, while others hypothesize certain silesaurids might have evolved into ornithischians, according to the paper.

Understanding silesaurids could shed light on which physical traits made dinosaurs so successful. But because these fossils are often missing crucial anatomical pieces, it’s hard to pin down their lineage.

“The problem is that we have a lot of material of early silesaurids, but the forms that are probably most related to ornithischians are rare,” Müller tells the New York Times’ Asher Elbein.

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The newly examined fossil was initially found in 2014 by physician Pedro Lucas Porcela Aurélio in a rock layer that dates to between 201 million and 252 million years ago—during the Triassic. He donated the fossil to a university in 2021, allowing paleontologists to get a close look at it, according to Reuters. The fossil represents one of the oldest silesaurids ever found.

“Being the first human to touch something from 237 million years ago is extraordinary,” Aurélio tells the publication. “It’s an indescribable feeling.”

When Aurélio gave Müller the fossil, it was covered in thick rock, and only the vertebrae were visible. But these bones revealed a curious trait about Gondwanax: The creature had three vertebrae in its hips, unlike other early relatives of dinosaurs, which had just two. This made Gondwanax seem more dinosaur-like, suggesting it might have been a true dinosaur, representing a rare example of a Triassic ornithischian, or a direct ancestor of that group, per the New York Times.

If that hypothesis is confirmed, the discovery would add as many as seven to ten million years to the history of ornithischians, Steve Brusatte, a paleontologist at the University of Edinburgh who was not involved in the study, tells the New York Times. And it would also rewrite the origin of dinosaurs, making them more common much earlier in the fossil record than previously thought.

But the scientists still need more fossil evidence to be able to state this as fact. “I wish I could say that this new silesaurid fossil solves the riddle once and for all,” says Brusatte to the New York Times, “but for me, it is still an open question.”

Alexa Robles-Gil | | READ MORE

Alexa Robles-Gil is a bilingual science journalist based in New York City. Her work has appeared in the Guardian, Undark, Inside Climate News and more.