'It's got legs!': 4-legged snake is a fossil find

The slab of stone in an obscure museum was labeled “unknown fossil vertebrate.” But when British paleontologist David Martill saw it, he knew at once that it was something extraordinary.

“I thought, ‘Blimey! That’s a snake!’ … Then I looked more closely and said, ‘Bloody hell! It’s got back legs!’” says Martill, of Britain’s University of Portsmouth. When he noticed the fossil also had front legs, “I realized we’d actually got the missing link between lizards and snakes.”

Martill and his colleagues say the fossil, dating back 110 to 125 million years, is the first snake ever discovered with four legs. It may or may not have been the granddaddy of all living snakes, but the creature that gave rise to today’s boas, rattlers and copperheads could’ve looked like this new specimen, the researchers say. The newly identified fossil also illuminates how early snakes survived the ferocious eat-or-be-eaten world of the Early Cretaceous.

One clue comes from the remains of a small animal – perhaps a salamander or frog – in the animal’s gut. The fossil snake also had a hinged jaw that allowed it to open wide and curved teeth for digging into big prey. All that suggests snakes were hunting critters other than insects from the very beginning.

Primitive-looking snakes of today subsist on insects, but the fossil shows “snakes really early on, 100 million years ago, were already eating meat,” says study co-author Nicholas Longrich of Britain’s University of Bath. “They were basically carnivores … from the get-go.”

The new specimen, as befits a proper snake, has a long, slender neck and back. The fossil coils and writhes on its slab, which the researchers take as a sign that it was able to squeeze its meals into submission. Thus its scientific name: Tetrapodophis amplectus, or “four-footed snake that embraces.”

“Huggy the Snake,”Longrich jokes, “because he hugged his prey.”

Huggy’s tiny limbs are equipped with weirdly long “fingers” and toes, reminiscent of the appendages of sloths or bats. Rather than using them to walk, it probably slithered over the ground in traditional snake fashion. Perhaps the appendages helped the snake grasp prey or clasp a mate. What the animal doesn’t have, Longrich says, are any swimming aids, which argues against the idea that snakes evolved from marine creatures.

One of the proponents of the ocean-origins hypothesis says that to his eye, Huggy isn’t even a snake. The specimen lacks “key features” of the vertebrae that would identify it as a snake, Michael Caldwell of the University of Alberta says via email.

But University of Arizona evolutionary biologist John Wiens, who like Caldwell is not affiliated with Team Huggy, says the new fossil is probably a snake, and a “very interesting” in-between animal at that. Study co-author Longrich points out that the fossil had more than 150 vertebrae in its back and neck and a layer of large, flat scales on its belly. Those traits are “uniquely snake-like,” he says.

The fossil, which was collected in Brazil at an unknown date, certainly struck Martill as a snake when he spotted it at Germany’s Burgermeister-Muller-Museum. At only 7 or 8 inches long, it’s no rival to the species Martill usually studies, but he doesn’t mind.

“I tend to work on pterodactyls and dinosaurs,” he says. “But I don’t mind pocket-size animals when they’re as exciting as this one.”