Four-legged snake fossil 'may unravel slithering mystery'
The first known fossil of a four-legged snake has been discovered by scientists who believe it may help unravel the mystery of how serpents lost their legs.
Dr Dave Martill, from the University of Portsmouth, said the fossil, which he found in a collection in a German museum, showed that snakes evolved from burrowing lizards and not from marine lizards.
The fossil, from Brazil, dates from the Cretaceous period and is 110 million years old, which the scientists say makes it the oldest definitive snake.
Dr Martill said: "It is generally accepted that snakes evolved from lizards at some point in the distant past. What scientists don't know yet is when they evolved, why they evolved, and what type of lizard they evolved from.
"This fossil answers some very important questions, for example it now seems clear to us that snakes evolved from burrowing lizards, not from marine lizards."
Dr Martill discovered the fossil as part of a routine field trip with students to Museum Solnhofen, Germany, which has a prestigious fossil collection.
He said: "The fossil was part of a larger exhibition of fossils from the Cretaceous period. It was clear that no-one had appreciated its importance, but when I saw it I knew it was an incredibly significant specimen."
Dr Martill worked with expert German palaeontologist Helmut Tischlinger, who prepared and photographed the specimen, and Dr Nick Longrich from the University of Bath's Milner Centre for Evolution, who studied the evolutionary relationships of the snake.
Dr Longrich, who had previously worked on snake origins, said: "A four-legged snake seemed fantastic and as an evolutionary biologist, just too good to be true, it was especially interesting that it was put on display in a museum where anyone could see it."
The snake, named Tetrapodophis amplectus by the team, is a juvenile and very small, measuring just 20 cm from head to toe, although it may have grown much larger. The head is the size of an adult fingernail, and the smallest tail bone is only a quarter of a millimetre long.
The front legs are very small, about 1cm long, but have little elbows and wrists and hands that are just 5 mm in length. The back legs are slightly longer and the feet are larger than the hands and could have been used to grasp its prey.
Dr Longrich said: "It is a perfect little snake, except it has these little arms and legs, and they have these strange long fingers and toes.
"The hands and feet are very specialised for grasping. So when snakes stopped walking and started slithering, the legs didn't just become useless little vestiges - they started using them for something else. We're not entirely sure what that would be, but they may have been used for grasping prey, or perhaps mates."
The snake also has the remains of its last meal in its guts, including some fragments of bone, which the team believes was probably a salamander, showing that snakes were carnivorous much earlier in evolutionary history than previously believed.
Tetrapodophis has been categorised as a snake, rather than a lizard, by the team because it has a lengthened body and not a tail, the snake-like teeth and hints on the fossil of a row of belly scales.
Tetrapodophis would have lived on the bank of a salt lake, in an arid scrub environment, surrounded by succulent plants and would probably have lived on a diet of small amphibians and lizards.
At the time, South America was united with Africa as part of a supercontinent known as Gondwana and the presence of the fossil suggests that snakes may originally have evolved on the ancient supercontinent, and only became widespread more recently.