Hello Biologists,

My question is:

I am curious about the evolution of snakes.  I have heard some talk of snakes evolving from mosasaurs - that snakes actually descended from mosasaurs!  Is this true?  How and when did snakes evolve?

Thank you for your time,
Peter

This is a very controversial idea, and still debated about a lot in the field. There is some neat anatomical evidence that supports it, but others still feel that monitor lizards and primitive snakes show that mosasaurs were more distantly related. The jury is largely out on this issue but leaning toward the favor of the classical view (snakes evolved from monitor lizard-like animals on land, not in the water), as far as I'm aware. Stay posted though, this story is still developing...

Hi Peter,

As John said the mosasaur-snake relationship is currently a controversial one.
Although the mosasaur-snake relationship does have some interesting anatomical evidence, no-one actually proposes that snakes evolved from the mosasaurs. Snakes appear to be the closest group living group to the mosasaurs, though not actually descended from them.

The earliest snake is known from near the end of the Early Cretaceous of Algeria, ~110 million years ago. It was a terrestrial species, that is unfortunately poorly known.
The earliest currently known mosasaur is ~98 million years ago, from the very beginning of the Late Cretaceous, and was marine.

One reason why people may think snake evolved from mosasaurs is that, at the same time as the first mosasaurs, snakes moved into the sea. These early sea snakes still had complete hind-legs unlike any snake living today.

If we take the mosasaur-snake relationship as being true, then mosasaurs and snakes evolved at a roughly similar times from the same type of lizard.