Fossil snake helped clarify the process of limb loss by its relatives

The skull of a modern snake, with the contour of the inner ear.

Evolution is a complex process, with a large number of intermediate links. It is rather difficult to determine how the process of evolution went in one way or another. For example, why did snakes lose their limbs? For what reason? For a long time it was believed that the reason is the transition of snakes to life in water.

An analysis of fossils, the remains of a fossilized snake that lived 90 million years ago, can change this view. As it turned out, snakes could begin to lose limbs when their ancestors switched to a new way of life - they began to live and hunt in burrows, which their descendants are doing now.

To analyze the remains of an ancient snake, scientists used tomography. More precisely, the skull of a snake was scanned, namely, the inner ear of Dinilysia patagonica, an animal close to modern snakes. The inner ear of snakes is responsible for hearing (which is logical) and for maintaining balance.

Scientists have created 3D models of the inner ear of fossil snakes, as well as models of the inner ear of modern snakes and lizards. As it turned out, the structure of this organ in animals that live and hunt in burrows differs significantly from the structure of the inner ear of animals that do not use burrows, or spend a minimum of time in them. In modern snakes living in water or on the surface of the earth, the inner ear is different from the "earth" snakes.

Discovered differences help specialists fill gaps in the evolution of snakes. It also turned out that Dinilysia patagonica is the largest snake that dug burrows and lived in them. An analysis of the structure of the snake’s skull helped scientists get clues as to what it looked like and what the common ancestor of all modern snakes did. Probably, this species also lived in holes.

Research results have already been published in Science Advances.

“The process of snakes losing limbs for a long time remained a mystery to scientists, but now it all boils down to the fact that the ancestors of snakes began to lose limbs as soon as they started digging holes and life in them. The inner ear of an ancient snake can provide a significant amount of information, ”says Hongyu Yi, a spokesman for the research team at the University of Edinburgh's Earth Sciences School.

Another specialist, Mark Norell, notes that making such a discovery 10 years ago was impossible. Only now, tomography has reached the required level of development.