A team of paleontologists, led by Dr Dave Martill from the University of Portsmouth, UK, has found a unique four-legged specimen in the Crato Formation of Brazil.

The snake, named Tetrapodophis amplectus, lived during the Early Cretaceous, around 110 million years ago.

At the time, South America was united with Africa as part of a supercontinent known as Gondwana. The presence of the oldest definitive snake fossil on the ancient supercontinent suggests that snakes may originally have evolved there, and only became widespread much more recently.

The specimen is a juvenile and very small, measuring just 8 inches (20 cm) from head to toe, although it may have grown much larger. It lacks the long, laterally compressed tail typically found in aquatic animals, suggesting that snakes did not evolve from marine ancestors.

But the most remarkable thing about this snake is the presence of two sets of legs.

The front legs are very small, about 0.4 inches (1 cm) long, but have little elbows and wrists and hands that are just five millimeters 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.

“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,” said Dr Martill, first author of a paper published in the journal Science.

“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.”

Tetrapodophis amplectus would have lived on the bank of a salt lake, surrounded by succulent plants.

The snake would probably have lived on a diet of small amphibians and lizards, trying to avoid the dinosaurs and pterosaurs that lived there.

“Tetrapodophis amplectus is a perfect little snake, except it has these little arms and legs, and they have these strange long fingers and toes,” added co-author Dr Nick Longrich from the University of Bath, UK.

“The hands and feet are very specialized 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.”

Interestingly, the snake also has the remains of its last meal in its guts, including some fragments of bone.

The prey was probably a salamander, showing that snakes were carnivorous much earlier in evolutionary history than previously believed.

“The preservation of the little snake is absolutely exquisite. The skeleton is fully articulated. Details of the bones are clearly visible and impressions of soft tissues such as scales and the trachea are preserved,” said Germany paleontologist Dr Helmut Tischlinger, co-author on the study.

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David M. Martill et al. 2015. A four-legged snake from the Early Cretaceous of Gondwana. Science, vol. 349, no. 6246, pp. 416-419; doi: 10.1126/science.aaa9208