How snakes got legless

Analysis of a reptile fossil has helped a team of scientists solve the evolutionary mystery of how snakes lost their legs.

The 90 million-year-old skull is giving researchers vital clues about how snakes evolved. Comparisons between CT scans of the fossil and modern reptiles indicate that snakes lost their legs when their ancestors evolved to live and hunt in burrows, which many snakes still do today.

The findings show snakes did not lose their limbs in order to live in the sea, as was previously suggested.

Scientists used CT scans to examine the bony inner ear of Dinilysia patagonica, a 2-metre long reptile closely linked to modern snakes. These bony canals and cavities, like those in the ears of modern burrowing snakes, controlled its hearing and balance.

The findings help scientists fill gaps in the story of snake evolution, and confirm Dinilysia patagonica as the largest burrowing snake ever known. They also offer clues about a hypothetical ancestral species from which all modern snakes descended, which was likely a burrower.

Dr Hongyu Yi, of the University of Edinburgh's School of GeoSciences, who led the research, said that the inner ears of fossils can reveal a remarkable amount of information, and are very useful when the exterior of fossils are too damaged or fragile to examine.

The study, published in Science Advances, was supported by the Royal Society.