Prehistoric reptiles are the extinct ancestors of the reptiles that exist today, such as snakes, lizards, and turtles. Reptiles developed slowly about 300 million years ago from creatures called amphibians. Amphibians had to lay their eggs in water. Reptiles were the first animals to lay eggs with shells. A reptile is eggs could be laid on land and would not dry up. This set prehistoric reptiles free to roam the earth and many different species developed. Later, birds and mammals evolved from reptiles.