The creepy new snake ancestor -- called Tetrapodophis amplectus -- is described in a paper published Thursday in Science.
"Snakes, they occupy a unique spot in the human imagination," study author Nicholas Longrich of the University of Bath, in Britain, said. "They come up as villains everywhere, from Harry Potter to the Bible. We dislike them so much because they're such great predators -- they ate a lot of our ancestors."
But how they came to be so fierce is a matter of some debate: Some paleontologists think that snakes evolved from marine creatures, but it is quite accepted now that snakes evolved from lizards, losing their limbs along the way. Scientists point to very primitive snake fossils that didn't live in the sea, indicating that the first snakes evolved from land lizards before some descendants chose to go for a swim.
This newly described species has a long, snake-like body and a flexible spine that hints at serious constriction capabilities. According to Longrich and his colleagues, it looks like an animal that might have burrowed under the ground, suggesting that it evolved from subterranean lizards that spent all their time beneath the Earth.
And unlike previously discovered ancient snakes, which had two limbs at most, this one seems to have retained all four. That's surprising, because many paleontologists have theorized that the lengthening of the body made limbs -- now useless -- disappear.
But Tetrapodophis amplectus may have used its limbs even as its body stretched out -- just not for walking.
"They would have moved in a serpentine fashion, like snakes today," Longrich said, "But the limbs aren’t just a scaled down, reduced, nonfunctional lizard limb, like you find in many ancient snakes. They’re very highly specialized."
Longrich described the long, slim fingers extending from each of the limb, which are all similar in length and have a slight curve to them.
"They could have used these limbs like grappling hooks to grab onto their prey," he said.
Indeed, the animal was preying on something not long before it died. Its stomach contains another vertebrate.
University of Florida's Martin Cohn, who wasn't involved in the study, told Nature Magazine that the combination of a complete set of limbs and a long, snake-like body could make the specimen "one of the most important fossils ever found."
But some paleontologists aren't sure that the fossil is a snake at all. Michael Caldwell of the University of Alberta told National Geographic's Ed Yong that he'd have to see the specimen in person to be convinced. “I think the specimen is important, but I do not know what it is,” Caldwell told Yong. Because the skull of the snake isn't very well preserved, many of the "snake-like" characteristics that Longrich and his colleagues have spotted may be subject to debate.
If it is indeed an early snake, the fossil could solve one more mystery as well: The geographical origin of serpents.
"You see a handful of very old, primative snakes in North America, and many more in South America and Africa," Longrich explained. He believes this new, unprecedentedly primitive snake came from South America (though this is also up for debate, since the fossil came from a private collection). In that case, he argues, the first snakes and their ancestors surely came from Gondwana -- the ancient super-continent that broke apart to form South America and Africa some 180 million years ago.
"Gondwana is really weird, everything there was very different," Longrich said. "Most of the things that originated there didn't make it, evolutionarily. But it looks like snakes might be the one big holdover from this weird ancient landmass."