The subclass Diapsida is one of the three major amniote reptile lineages (along with Anapsida and Synapsida). It is one of the most diverse vertebrate groups. First seen in the Late Carboniferous (c. 315 mya), it includes all living reptiles except turtles, in other words, lizards, snakes and crocodiles, as well as the birds, and many extinct groups including dinosaurs, pterosaurs and ichthyosaurs. Each of the six major subgroups - the Lepidosauria, Euryapsida, Ichthyosauria, Crocodylomorpha, Dinosauria and Class Aves - has its own site which describes it in more detail. These can be found on the Chordata homepage.