The first turtles were Proganochelys and Proterocheris from the Late Triassic. Turtles have the anapsid type skull. The jaws are toothless, and turtles have a horny beak that is used for snipping plants or insect cuticles. The turtle shell (the carapace) is the most characteristic feature; it serves as a from of protection.
The lepidosaurs are the most diverse group of reptiles alive today. The first lepidosaurs were the sphenodontians, ancestors of the living tuatara, Sphenodon. The lepidosaurs radiated during the Jurassic, with the appearance of lizards in the Mid Jurassic, and snakes in the Early Cretaceous. Snakes and lizards live worldwide, although most abundantly in tropical regions. The tuatara is resticted to New Zealand, and it is often called a 'living fossil'.
|Skeleton of a Boa Constrictor|
Crocodilians arose in the Late Triassic. At that time, they were small, bipedal insect-eaters. More typical aquatic forms appeared in the Early Jurassic, and Mesozoic forms diversified on land, in lakes and rivers, and in the sea. There was a further diversification of crocodilians during the Tertiary, but today only some 15 species remain - the alligators, crocodiles, and gavials - well known from tropical regions around the world.