Snakes crawled among Jurassic dinosaurs, new timeline says

Just call it the Jura-sssss-ic Period. Newly identified fossils suggest that snakes slithered through much of the golden age of the dinosaurs, a finding that pushes back the fossil record for snakes by 70 million years.

Ancient skulls with features similar to modern snakes tipped paleontologists off to the new timeline, they report January 27 in Nature Communications.

The fossils also indicate that snakes evolved their flexible skulls before they stretched out and lost their legs, the authors say.

“One of the major ideas about the evolution of snakes is that the long body evolved first because it allows constriction, an ancient predation strategy. The highly mobile skull came later,” says Krister Smith, a paleontologist at the Senckenberg museum in Frankfurt am Main, Germany. “The authors challenge this and present a new head-first hypothesis.”

Before the new finds, the earliest known snakes lived about 100 million years ago, during the Cretaceous Period.

Michael Caldwell, a paleontologist at the University of Alberta in Canada, identified the first of the new fossils while perusing a collection of lizards from the earlier Jurassic Period in England. Among the remains were a few bones that were in fact very old snakes, he said.

Wondering if other ancient snakes had been mislabeled or overlooked, he and his team spent the next 10 years sifting through museum fossil collections. Ultimately, they found four new species of snake from what are now England, Portugal and Colorado. The fossils dated from 143 million to 167 million years old, from the mid-Jurassic to early Cretaceous periods.

While alive, the newly identified snakes probably had four limbs and shorter bodies than their living relatives, Caldwell says. “These things had specialized features of snake skulls 167 million years ago. That probably indicates that … the snake innovation was about the skull and feeding ecology, not becoming long and legless.”

The skulls of the fossils share a number of features with later snake fossils and living snakes. These include teeth that curve backward and that sit in sockets, as opposed to sitting in a single shallow groove like lizards’ teeth. The fossils also sport bones in the roof of the mouth that can shift, allowing the jaws to spread apart for bulky meals. And the fossils lack bony protrusions that hold the upper jaw in place in lizards (and in other four-limbed animals, including humans).  

“Snakes have very mobile skulls,” says Caldwell. The skulls from the ancient snakes aren’t as flexible as those seen in some living snakes, but do resemble the more fixed and rigid skulls of today’s boas and pythons.

Most of the bones were skulls, so the researchers cannot be certain what the rest of the snakes’ bodies looked like. But snake fossils from about 70 million years later still have hind limbs, leading the researchers to conclude that the essential “snakeness” of the skull was already in place before the animals lost their legs.

“With only bits of skeleton to work with, it’s easy to make a mistake,” says Nicholas Longrich, a paleontologist at the University of Bath in England. “But I think [Caldwell] and his team make a good case for these fossils being related to snakes. These fossils are the best candidates we’ve seen yet for early snake relatives.”