The mystery of when and why snakes lost their limbs is closer to being solved following the discovery of the world's oldest snake fossils.
Four species have been found dating to between 140 and 167 million years ago - 70 million years older than the previous oldest specimen. One of the species reached about four feet in length and would have eaten dinosaurs for dinner.
Published in the journal Nature Communications, the findings provide new evidence about the origins of snakes.
Lead author Michael Caldwell, from the University of Alberta said their findings show snake evolution is far more complicated than previously thought – at present there is a huge knowledge gap from between 140 and 100 million years ago, where there are no snake fossils.
The appearance of snakes 100 million years ago was not an explosive radiation of the reptiles. Instead, the new species show they were evolving towards elongated, limb-reduced bodies millions of years earlier.
The four species came from ancient Europe and North America.
Caldwell told IBTimes UK that the newly discovered species had snake-like heads, no venom or fangs, back legs, possibly front legs and far shorter bodies with elongated necks.
The smallest snake, Eophis underwoodi, lived 167 million years ago and was about 10 inches long. He said it probably ate small minnows, insects and tadpoles.
Parviraptor estesi originated 144 million years ago and lived around freshwater snails. At this time, there were turtles, dinosaurs, mammals, fish and crocodiles.
Dating to 155 million years ago, Diablophis gilmorei was also very small and was found in rocks in Colorado. The name means devil snake after the local creek where it was found.
From the same era was Portugalophis lignites, the largest of the snake fossils found. This species reached up to four feet in length and had a large head. It was likely to have eaten larger prey, including small mammals, dinosaurs and lizards.
Explaining why he thinks snakes lost their legs, Caldwell said you see limb loss across nature, but why it occurs remains a mystery. "It happened as a genetic and developmental event, a plasticity in the group, that didn't cause their extinction, they succeeded, and then succeeded around the adaptation turning it to their advantage," he said.
"Today there are 3,500-ish species of limbless living snakes. I would hazard a guess that there are thus 3,500ish reasons for why limblessness works well."