Snake Ancestors Had Four Legs: Ancient Fossil Reveals Evolution of Snakes

First Posted: Jul 24, 2015 09:00 AM EDT

Scientists have made an unusual discovery. They've uncovered a snake fossil that had four legs, which may tell them a bit more about how snakes made the transition from lizards to serpents.

The new fossil is actually the first-known fossil of a four-legged snake. Dating back to the Cretaceous period about 110 million years ago, it's the oldest definitive snake yet found.

"It is generally accepted that snakes evolved from lizards at some point in the distant past," said Dave Martill, one of the researchers, in a news release. "What scientists don't know yet is when they evolved, why they evolved, and what type of lizard they evolved from. This fossil answers some very important questions, for example it now seems clear to us that snakes evolved from burrowing lizards, not from marine lizards."

The fossil was actually found in a museum. It was part of a larger exhibition of fossils from the Cretaceous period, and only when Martell studied it more closely did he realize what an important specimen it was.

"A four-legged snake seemed fantastic and as an evolutionary biologist, just too good to be true," said Nick Longrich, one of the researchers. "It was especially interesting that it was put on display in a museum where anyone could see it."

The snake has now been named Tetrapodophis amplectus, and is a juvenile of its species. Although it measures just 20 cm from head to toe, it may have grown much larger. The head is the size of an adult fingernail, and it possesses two sets of legs.

"It is a perfect little snake, except it has three little arms and legs, and they have these strange long fingers and toes," said Longrich. "The hands and feet are very specialized for grasping. So when snakes stopped walking and started slithering, the legs didn't just become useless little vestiges-they started using them for something else. We're not entirely sure what that would be, but they may have been used for grasping prey, or perhaps mates."

The findings are published in the journal Science.