A new science report solves the puzzle of how snakes lost their legs.
A 90 million-year old fossil of a snake skull is telling scientists why snakes lost limbs. Comparisons between CT scans of the fossil and today's snakes indicate that snakes lost their legs when their ancestors to started to live and hunt in burrows and not as previously thought to live in the sea.
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Dr Hongyu Yi, of the University of Edinburgh's School of GeoSciences, who led the research, said: "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. The inner ears of fossils can reveal a remarkable amount of information, and are very useful when the exterior of fossils are too damaged or fragile to examine."
Scientists at the University of Edinburgh used CT scans to examine the bony inner ear of Dinilysia patagonica, a 2-meter long ancient reptile closely linked to modern snakes. These bony canals and cavities, like those in the ears of modern burrowing snakes, controlled its hearing and balance.
They built 3D virtual models to compare the inner ears of the fossils with those of modern lizards and snakes. Researchers found a distinctive structure within the inner ear of animals that actively burrow, which may help them detect prey and predators. This shape was not present in modern snakes that live in water or above ground.
The findings confirm that Dinilysia patagonica as the largest burrowing snake ever known. They also offer clues about a hypothetical ancestral species from which all modern snakes descended, which was likely a burrower.
Mark Norell, of the American Museum of Natural History, who took part in the study, said: "This discovery would not have been possible a decade ago - CT scanning has revolutionized how we can study ancient animals. We hope similar studies can shed light on the evolution of more species, including lizards, crocodiles and turtles."
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The study titled "The burrowing origin of modern snakes" is published in Science Advances.