The first known fossil of a four-legged snake has been discovered by a scientist on a routine field trip to a museum. It is hoped the find will help unravel the mystery of how serpents lost their legs. Dave Martill, from the University of Portsmouth, found the fossil in a collection in a German museum. It shows snakes evolved from burrowing lizards and not from marine lizards, Dr Martill said. The fossil from Brazil dates from the Cretaceous period and is 110 million years old, making 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 made the discovery on a trip with students to Museum Solnhofen, 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 fossil. Nick Longrich from the University of Bath’s Milner Centre for Evolution studied the evolutionary relationships of the specimen. Dr Longrich 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 was named Tetrapodophis amplectus by the team. It is a juvenile and very small, measuring 20cm (7.8in) from head to toe, although it could have grown much larger. Its 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 also very small, about 1cm long, with little elbows and wrists and hands 5mm 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 has the remains of its last meal in its stomach, including fragments of bone, which the scientists believe was probably a salamander. This shows snakes were carnivorous much earlier in evolutionary history than previously thought. Tetrapodophis has been categorised as a snake, rather than a lizard, because it has a lengthened body and not a tail, snake-like teeth and hints on the fossil of a row of belly scales. It would have lived on the bank of a salt lake, in an arid scrub environment, surrounded by plants and would probably have survived on a diet of small amphibians and lizards.
South America was united with Africa at the time as part of the Gondwana supercontinent.
The presence of the fossil suggests snakes may have originally evolved on the ancient supercontinent, and only became widespread more recently.