How snakes got legless

High powered X-ray reveals 95 million year old snake leg. Image: A.Houssaye

A new study has confirmed a missing link in snakes’ legless evolution.

It is difficult to determine whether snakes evolved from terrestrial lizards or from ocean dwelling reptiles. With only three snake specimens showing preserved leg bones having been discovered, the fossil record evidence is scant.

A new study conducted by Alexandra Houssaye from the Museum National d’Histoire Naturelle in Paris has sought to have a better look at the fossilised snake legs to see what they could tell us. With the help of the European Synchrotron Radiation Facility in Grenoble, France, Houssaye X-rayed a 95 million year old snake fossil to reveal its hidden leg. The specimen was a species called Eupodophis descouensi (one of the very few legged snake species).

The fossil shows only one short leg and it was thought that the other leg way hidden within the rock. Using the coherent synchrotron X-ray beam, which shows 1000 times more detail than a hospital CT scanner, Houssaye was able to get a 3D image of the fossil, revealing the second leg, which was bent at the knee.

The leg bones are small and have anklebones, but no foot or toe bones. This suggests that the species grew slowly, or for a shorter period of time, inhibiting the leg bones from developing. The leg bones are also similar to that of modern terrestrial lizards, which suggests that snakes evolved from lizards.

“The revelation of the inner structure of Eupodophis hind limbs enables us to investigate the process of limb regression on snake evolution,” said Houssaye in a statement.

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