A 90-million-year-old snake skull discovered in Argentina shed light on how snakes lost their legs. The widespread belief is that these animals shredded their legs to swim better when they inhabited aquatic settings. The newly unearthed fossil suggested that legs may have been a disadvantage in the animals' evolution whose ancestors pursued preys in very narrow warrens.

The researchers examined the snake fossil's inner ear using Computed Tomography (CT). They found that the Dinilysia patagonica, the modern snake's two-meter long ancient cousin, had a unique structure located in their bony canals and cavities which could help in prey and predator detection. This structure is also found in modern day nestling lizards and snakes but missing in snakes who live above ground or in the water. Snakes use their inner ear for balancing and hearing, which aid them in prey and predator detection.

The research concluded that the Dinilysia patagonica is the biggest burrowing snake to date and that the species' burrowing lifestyle preceded modern snakes. The researchers also hypothesized that modern-day crown snakes originated from the burrowing snakes such as the Dinilysia patagonica.

"How snakes lost their legs has been a mystery to scientists but it seems this happened when their ancestors became adept at burrowing," said Dr. Hongyu Yi, the study's lead scientist from the School of GeoSciences at the University of Edinburgh. Yi added that fossils' inner ears are useful sources of information, particularly when the fossils' exteriors are too delicate or broken.

American Museum of Natural History's Mark Norell added that a decade ago, the discovery of the inner ear's structure wouldn't have been possible. The use of CT scanning has modernized and improved how scientists study the fossils of ancient animals. A CT scan is a type of X-ray that creates three dimensional images of skeletal structures and organs in vivid detail.

 Norell, who was part of the study, shared the hope that similar studies on ancient animals could fill in the evolution puzzle of other species such as turtles, crocodiles and lizards.

The researched was published in the Science Advances journal on Nov. 27.