Today there are 6,800 reptile species on earth; the major groups are alligators and crocodiles, turtles, lizards, and snakes.

Reptiles are tetrapods and amniotes, animals whose embryos are surrounded by an amniotic membrane. Today they are represented by four surviving orders: crocodilia (crocodiles, caimans and alligators), sphenodontia (tuataras from New Zealand, squamata (lizards, snakes and amphisbaenids - "worm-lizards"), and testudines (turtles).