The fossil, found in the Crato Formation in northeastern Brazil, is of the newly discovered species Tetrapodophis amplectus. It lived during the Early Cretaceous 146 to 100 million years ago.
While the animal has many classic snake features, such as a short snout, long braincase, elongated body, scales, fanged teeth and a flexible jaw to swallow large prey, its four legs are a dramatic departure.
Scientists believe the limbs were not used for locomotion, however, and were instead used for grasping.
The authors of a study, reported in Science, base their assumption on the shorter exterior digits and lengthened second digit of the reptile’s limbs.
Nevertheless, the fossil shows the typical vertebrae structure seen in modern-day snakes that allows for the extreme flexibility required to constrict prey.
But it lacks the long, laterally compressed tail typically found in aquatic animals, further suggesting that snakes did not evolve from marine ancestors.
Dr Dave Martill, from the University of Portsmouth, found the fossil in a German museum collection.
“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,” he told reporters.
Bill Condie is a science journalist based in Adelaide, Australia.
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