Question: what did snakes evolve from

Ceri-Wyn Thomas answered on 16 Jun 2010:

Ooh fun question! Snakes are thought to have evolved from lizards based on fossil evidence and from comparing the overall anatomy of snakes with certain lizard groups. In particular snakes are thought to have evolved from burrowing lizards so the transparent eyelids and lack of external ears we see on modern snakes may have evolved to cope with their old burrowing lifestyle. There are also fossils which look like intermediates between snakes and lizards where they have only one set of front limbs.

Also, modern snakes like pythons and boas bear the remnants of hind limbs on their skeletons (we call the vestigial structures- another example would be the appendix in humans!). The vestigial hind limbs on modern snakes are called anal spurs (unfortunate name!) and are now co-opted for use in mating. Snakes now show no evidence of front limbs so perhaps the genes that control for frontal limb growth are no longer present/used during embryological development in modern snakes.