Although snakes are descended from limbed squamates ('lizards'), all known snakes lack well developed legs and their nearest lizard relatives have yet to be identified1–4. Here we provide compelling evidence that the Cretaceous squamate Pachyrhachis problematicus, previously interpreted as a varanoid lizard5–7, is actually a primitive snake with a well developed pelvis and hindlimbs. Pachyrhachis is the sister-taxon of all other snakes. The skull exhibits most derived features of modern snakes, and the body is slender and elongated. But unlike other snakes, Pachyrhachis retains a well developed sacrum, pelvis and hindlimb (femur, tibia, fibula, tarsals). Pachyrhachis was marine, and provides additional support for mosasauroid–snake affinities.
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Caldwell, M., Lee, M. A snake with legs from the marine Cretaceous of the Middle East. Nature 386, 705–709 (1997). https://doi.org/10.1038/386705a0
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