Archosaur fossils are forcing scientists to rethink evolution of dinosaurs

Scientists have identified one of the earliest known dinosaur relatives — and it doesn’t look anything like they expected.

Researchers had thought that the oldest dinosaur cousins would look rather like small, two-legged dinosaurs themselves. Instead, Teleocrater rhadinus actually stretched 7 to 10 feet long, boasted a long neck and tail, and walked on all fours.

The findings, described in the journal Nature, could force paleontologists to redraw their understanding of dinosaurs’ origins, as well as the nature of the reptiles that came before them.

“This just goes to show that there’s a lot more out there that we just didn’t know, especially the early history of the larger group that dinosaurs belonged to: Archosauria,” said lead author Sterling Nesbitt, a vertebrate paleontologist at Virginia Tech in Blacksburg.

Dinosaurs are part of a larger group known as the archosaurs — a lineage of reptiles that split into a “bird-line” branch that includes pterosaurs, dinosaurs and birds, and a “crocodilian” branch whose living members today include crocodiles and alligators.

Paleontologists have long tried to predict what those early bird-line reptiles looked like, soon after the split with the crocodilian branch. But they haven’t been able to do so because of the large gaps in the fossil record of the period before dinosaurs emerged in the mid-to-late Triassic Period, roughly 230 million years ago. They have wondered: Which dinosaur traits are unique to dinosaurs, and which are shared with archosaurs? Without a wide range of older archosaur fossils, it was difficult to say for sure.

Still, many figured that the line of animals that gave rise to the flying reptiles known as pterosaurs, and later the dinosaurs, which themselves gave rise to birds (the only surviving member of the bird-line branch), might have originally come from a chicken-size, twolegged, dinosaur-like archosaur.

The Teleocrater fossils described by Nesbitt and his colleagues may be proving that idea wrong. This species isn’t exactly new to science: Paleontologist F. Rex Parrington first found fossils in Tanzania in 1933, and English paleontologist Alan J. Charig (a posthumous co-author of this paper) characterized the bones roughly two decades later. But the first specimen was missing crucial bones that would have allowed Charig to tell whether this was a bird-branch or crocodile-branch species of archosaur.