Snakes lost their legs yet kept a lizard's deep ancestry
Serpentes are limbless squamate reptiles on every continent but Antarctica, missing from Ireland, Iceland, Greenland, New Zealand, and many small Atlantic and Pacific islands. Most species lack venom; those that have it mainly subdue prey with neurotoxins, hemotoxins, and related cocktails delivered through fangs.
Snakes are lizards that lost their legs. Genomes, comparative anatomy and fossils all agree on that descent, and the leading idea is that they arose from burrowing lizards in the Cretaceous. Najash rionegrina, a two-legged snake relative from 95 million years ago, lived on land, had a sacrum, and already showed some of the loose skull joints of modern snakes. The oldest true snakes known are marine simoliophiids such as Haasiophis terrasanctus from the West Bank, 112 to 94 million years old. A four-legged fossil from Brazil, Tetrapodophis, was hailed in 2015 as an early snake, but a 2021 study placed it among extinct marine lizards; a snake-like body has evolved at least 26 times.
No living snake has front legs, a result of Hox gene changes that gave almost every vertebra ahead of the hips the same chest-like identity. Pythons and boas still carry tiny clawed spurs, remnants of hind limbs used to grip during mating. A skull with few sutures and highly mobile joints lets snakes swallow large prey whole.
They move by undulating, creeping in straight lines, bunching like a concertina or sidewinding, and some tree snakes glide by spreading their ribs. Around 30 families and more than 4,170 species live on every continent except Antarctica, ranging from the 10.4-centimetre Barbados threadsnake upward, though Ireland, Iceland and New Zealand have none. Many modern groups appeared in the Paleocene after the dinosaurs died, and North American grasslands in the Miocene brought the first vipers and elapids there.
The word comes from a Proto-Indo-European root meaning to creep, which also gave English sneak and Sanskrit nāga.
Source: Snake
