Snakes evolved from burrowing ancestor, new data suggest

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The mother of all snakes got its start underground.

X-ray images of snake and lizard skulls suggest that modern snakes’ ancestors burrowed rather than swam, scientists report November 27 in Science Advances.

The study is the latest to suggest that snakes evolved from land lizards that lost their limbs while adapting to a slithery, subterranean lifestyle (SN: 8/22/15, p. 10). Another theory posits that today’s snakes descended from marine reptiles — with a svelte body and lack of legs serving as adaptations to move through a watery home.

Paleontologists Hongyu Yi of the University of Edinburgh and Mark Norell of the American Museum of Natural History in New York City used X-ray scans to build 3-D virtual models of the inner ears of 44 fossil and modern reptile species.

Snakes use the inner ear, a tiny structure within the skull, for balance and hearing. The inner ears of snakes living in different environments have telltale shapes, the researchers found. Burrowers’ inner ears appear more inflated than those of other reptiles — like a balloon wrapped with a piece of cord. Such a structure has been linked with low-frequency hearing, and would have helped underground snakes detect the rumbling vibrations of predators or prey.

Dinilysia patagonica, a Late Cretaceous relative of modern snakes that lived roughly 90 million years ago, also had the balloon-shaped inner ear cavity of a burrower, Yi and Norell report. And an analysis of the snake family tree suggests that modern snakes’ early ancestors did too.