Rare snake fossil sheds light on early reptile evolution

TORONTO, June 21 (UPI) -- Why did snakes evolve long, limbless bodies? It is a question biologists have been trying to answer for decades.

In a quest for clarity on the subject, researchers at the University of Toronto have turned their attention to a rare Brazilian fossil, the tiny remains of a snake-like species that lived 110 million years ago.

Tetrapdophis amplectus is considered the first and oldest snake. Its discovery and identification by a team of British scientists was only announced just last year. Unlike modern snakes, it boasts legs. Four small, paddle-like legs protrude from its hind quarter.

Finding the proper place for Tetrapdophis amplectus on the evolutionary timeline is key to understanding why the species' successors ditched the legs altogether. And that's what a Canadian-Australian research team has done.

Previously, scientists suggested the first snakes were worm-like burrowers. The latest investigation of Tetrapdophis amplectus, detailed in the journal Cretaceous Research, suggests the earliest snakes were most closely related to aquatic lizards. Long, limbless bodies enabled eel-like swimming.

Researchers determined that the body shape of Tetrapdophis amplectus, its long tail and tiny legs, is unlike those of burrowing snakes and lizards. Its weak, less-ossified bones recall those of ancient aquatic lizards.

"This exquisite tiny fossil is very slender, with limbs that are certainly not suited for burrowing," Robert Reisz, a biologist at the University of Toronto, said in a news release. "Instead, it shares features with aquatic lizards from the Late Cretaceous. Tetrapodophis may be closely related to snakes and resembles a snake, but probably is not a snake proper."

"The radical new ideas about the aquatic habits of Tetrapodophis add to the debate, and helps cement this tiny reptile as one of the most important and controversial fossils of our times," Reisz concluded.