Snakes are uncommon as fossils. They have lightly constructed skeletons and skulls comprised of separate moveable sections and so are generally too fragile to preserve well. They were the last major group of reptiles to appear in the fossil record. One of the earliest known forms was Dinilysia, meaning 'terrible destroyer', which lived in the Early Cretaceous period. It seems likely that snakes evolved from aquatic lizards, although most have now returned to life on land.

All snakes are active hunters, using a variety of methods to kill their prey. Dinilsia was an early type of constrictor and so killed by wrapping its coils around its prey and asphyxiating it. The more specialised poisonous snakes are not thought to have evolved until the middle of the Tertiary period, perhaps 30 million years ago.