Current evidence suggests that snakes started to evolve less than 150 million years ago, but the debate about the evolutionary origins of snakes have not yet been definitively resolved, despite more than 100 years of research.
There are two competing theories. The first suggests that snakes evolved from land-based lizards which burrowed. Eventually losing their fore-limbs and then the hind-limbs.
An alternative hypothesis, based on morphology, suggests the ancestors of snakes were related to Mosasaurs — extinct water-based reptiles from the Cretaceous — which in turn are thought to have derived from Monitors (Varanidae) and Water Monitors (Lanthanotidae) of the Old World.
Recent DNA studies have not been able to definitively clarify their origin.