The earliest known snakes slithered around dinosaurs and likely ate the behemoth's eggs and young during the heart of the Middle Jurassic when dinosaurs were becoming the dominant predators on land.
Four newly discovered ancient snake fossils date the reptiles to between 140 and 167 million years ago, according to a new study, published in the journal Nature Communications. The earliest date is nearly 70 million years older than the previous record of ancient snake fossils.
Lead author Michael Caldwell explained to Discovery News that it is "very likely that snakes ate young dinosaurs or preyed upon their eggs."
"A very good example comes from the Late Cretaceous of India where a well preserved snake was found in a sauropod dinosaur nest with embryos of the dinosaur still in the egg," added Caldwell, who is the president of the Canadian Society of Vertebrate Paleontology and is chair of the University of Alberta's Department of Biological Sciences.
The oldest known snake, Eophis underwoodi, was unearthed in Southern England. It was small, although it could have been a juvenile when it died, and lived in a swamp or marsh environment 167 million years ago.
The second oldest is Diablophis gilmorei, which lived in a river or swamp area in what is now Colorado 155 million years ago. The largest snake of the quartet, Portugalophis lignites, is the same age, but lived in an ancient swamp in what is now Portugal. The youngest snake, Parviraptor estesi, dates to 140 million years ago and hailed from a lake region full of snails and algae in Western Europe.
"All of these snakes were living in or near water sources, at least close enough that when they died, their remains were preserved in rocks deposited in water," Caldwell said.
He added that, in addition to dinosaurs, the ancient snakes coexisted with pterodactyls, early mammals, crocodiles, lizards, amphibians, many kinds of fishes, and numerous other types of animals. Caldwell thinks that snakes preyed upon many of these species, and vice versa.
The prior fossil record suggested that snakes suddenly emerged and went through an explosive radiation around 100 million years ago. Now it's known that the process happened gradually, with snakes evolving their characteristic limbless, slithery bodies over a lengthy period of time.
The consensus is that snakes evolved from an as-of-yet unknown lizard ancestor, losing their forelimbs, shoulder girdles and breastbones along the way. It is even possible that the earliest snakes still retained short bodies and large legs from their lizard ancestors. Caldwell said that Eophis and its ancestors must have evolved as snakes much earlier than the Middle Jurassic, so even older, more primitive snakes are theorized to have existed.
There is also a chicken and egg question: Which came first, the snake's loss of limbs or its characteristic skull? Caldwell says it is possible that the skull emerged first.
He explained that, compared to the skulls of non-snake lizards, "the snake skull is more mobile as a result of reduced sutures and bony contacts, and ‘gets out of the way,' so to speak, when a snake eats large prey."
"As it appears that this feature evolved early on in snake evolution," he continued, "it looks as though some of the success of the snake feeding strategy is tightly linked to the early evolution of the skull within the group."
Jean-Claude Rage of the Museum National d'Histoire Natural, Paris, told Discovery News that the new study is "convincing." He continued, "One of the most unexpected issues is that, during the early evolution of the group, the achievement of the snake skull preceded that of the elongate, legless snake body." Rage expects additional ancient snake fossils to be found.
Michael Lee, an associate professor and snake expert at The University of Adelaide, said that the fossils Caldwell and his team studied "are the oldest fossil snakes by a very long margin -- 70 million years. This is a vast amount of time, longer than the Cenozoic, which is the age of mammals."
"What did snakes do during this 70 million year interval?" Lee asked. "We can only guess, until new fossils are unearthed."