(File photo)

WASHINGTON, Nov. 27 -- Researchers analyzing a 90-million-year-old fossil skull of an extinct reptile from Argentina said Friday they may have solved an evolutionary puzzle about how snakes lost their legs.

Their results, published in the U.S. journal Science Advances, showed that snakes lost their limbs when their ancestors evolved to live and hunt in burrows, which many snakes still do today.

Some scientists have previously argued that limblessness in snakes was due to an adaptation for swimming in the ocean, although the prevailing hypothesis about snake evolution is that they were ancestrally terrestrial burrowers.

In the new study, scientists used CT scans to examine the bony inner ear of Dinilysia patagonica, a two-meter long reptile closely linked to modern snakes.

Then, they built 3D virtual models to compare the inner ears of the fossils with those of modern lizards and snakes and determined that the extinct snake's ear appears to be that typical of terrestrial burrowing animals.

Dinilysia patagonica possesses a large, spherical vestibule in its inner ear which enhances sensitivity to low-frequency vibrations, they said.

This vestibule was similar in size to that found in modern snakes known to perceive low-frequency ground vibrations and similar to those found in burrowing species that use low-frequency ground vibrations to detect prey.

"How snakes lost their legs has long been a mystery to scientists, but it seems that this happened when their ancestors became adept at burrowing," study author Hongyu Yi of the University of Edinburgh's School of GeoSciences said in a statement.

The findings may help scientists fill gaps in the story of snake evolution, and confirm Dinilysia patagonica as the largest burrowing snake ever known, they added.