Archosauria (class Reptilia) A subclass of diapsid reptiles that includes the orders Crocodilia, Ornithischia, Saurischia, Pterosauria, and Thecodontia. Thecodontians were ancestral to the other groups and appeared at the base of the Triassic. Archosaur is derived from the Greek arkho, to rule, and saura, lizard.

Archosauria (archosaurs) Infraclass of diapsid reptiles, including the crocodiles, dinosaurs, pterosaurs, and thecodontians. Thecodontians were ancestral to the other groups and appeared at the base of the Triassic. The term ‘archosaur’ is from the Greek words arkhi (‘chief’ or ‘leading’) and saura (‘lizard’).