A 90 million year old skull has unlocked the secret to an evolutionary mystery: how snakes lost their legs.
Until geoscientist Hongyu Yi, from the University of Edinburgh, scanned the fossilised remains of the inner ear of the two meter long snake descendent, the Dinilysia patagonica, it was widely believed that snakes lost their legs so they could live in the sea.
Instead, the results of Yi’s work indicate that it is likely to be the opposite. Snakes lost their legs when their ancestors evolved to live and hunt in burrows, the newly published research shows.
Yi, along with researchers from the American Museum of Natural History, built 3D models to compare the inner ears of the fossils with those of modern snakes and reptiles.
The CT scans produced by the researchers allowed them to build a picture of the animal’s skull, where they found a structure inside the ear of the animals which is similar to those of modern snakes that burrow.
“We wouldn’t have known that just looking at the outside structure of the skull,” the Edinburgh-based researcher told WIRED.
“That’s surprising but it fits the hypothesis that snakes actually started off as burrowers. So they were at least adapted to that lifestyle, or perhaps hunting underground, they will be able to locate and run away from predators and to detect their prey underground.
Archaeologists have discovered several species of fossilised snakes that have limbs, and earlier this year a four-legged snake ancestor was found. The find of the animal hinted that snakes evolved on land, rather than at sea or in water.
The latest research paper, published in Science Advances and described as “the first quantitive analysis of the fossil” by Yi, says the Dinilysia patagonica share a “large spherical vestibule, large foramen ovale, and slender semicircular canals” all in the inner ear with modern burrowing creatures.
Yi said: “I set out and I had this idea of looking at the organs relating to their function, because we had the CT technique now available.
“So I thought it would be worth reconstructing some organs for fossil snakes and see from the fossil itself what kind of environment they were adapted to.”
Form the reconstructions it was possible for the researchers to conclude that snakes evolved to lose their legs when their ancestors became adept at burrowing
The ability to scan the fossils, using a CT scanning method based on x-rays, also gives the researchers the potential to look inside the ancient fossils: “It’s very important for fossils as we can’t crack them open,” Yi said.
“We would scan them rotating in 360 degrees getting thousands of images of each items.”
From the images a model of the internal structures of the head could be built. The technique also offers the potential to also look at how other animals have evolved, based on their fossils and comparing them to modern day creatures.
“This discovery would not have been possible a decade ago — CT scanning has revolutionised how we can study ancient animals,” Mark Norell, of the American Museum of Natural History, who took part in the study said in a press release about the discovery.
“We hope similar studies can shed light on the evolution of more species, including lizards, crocodiles and turtles.”