LIFE × EVOLUTION

How Snakes Lost Their Legs

~128 to 95 million years ago

Phanerozoic · Mesozoic · Cretaceous

Snakes did not shed their limbs in one move. A whole early branch kept a pelvis and working hind legs while the body was already long and the skull was already losing bones, one by one, in the sequence that ends in the loose jaw that lets a snake swallow prey wider than its own head. Where they started is the open question: limbed snakes from the Cretaceous seas of the Middle East argued for a swimming ancestor, and a Patagonian snake with a sacrum and functional hind legs argues for a land ancestor instead, burrowing or ground living.

Why it matters

Vertebrates have lost their limbs dozens of times over, and it almost never yields more than a handful of species in a single habitat. Snakes are the exception: four thousand species, and predators that swallow animals larger than themselves. What no other limbless lineage has is a skull that comes apart.

Dating & uncertaintyDisputed

Where snakes came from is still debated. The limbed snakes of the marine Cretaceous of the Middle East supported a sea-going ancestor; the Patagonian material, with its sacrum, its working hind legs and later its skulls preserved in three dimensions, currently makes the better case, and it puts the origin on land, in a burrowing or ground living animal. On that reading, snakes with hind limbs were not a brief passage but an early radiation that lasted.

Sources

1. Apesteguía & Zaher (2006), Nature · A Cretaceous terrestrial snake with robust hindlimbs and a sacrum
2. Garberoglio et al. (2019), Science Advances · New skulls and skeletons of the Cretaceous legged snake Najash, and the evolution of the modern snake body plan
3. Caldwell & Lee (1997), Nature · A snake with legs from the marine Cretaceous of the Middle East

Earth history as one day

23:19:2440 min 36 s before midnight

if Earth’s 4.54 billion years were compressed into a single day