within this lineage are the Archosaurs (ruling reptiles) most of which are now extinct except crocodiles and alligators (Order Crocodylia). Extinct Archosaurs included the famous dinosaurs represented by two orders; Saurischia (lizard-hipped dinosaurs with a triradiate pelvis) and Ornithischia (bird-hipped dinosaurs with a tetraradiate pelvis), the flying pterosaurs (Order Pterosauria) and