any of an order (Thecodontia) of reptiles of the Permian and Triassic periods, believed to be ancestors of the dinosaurs and crocodilians
See thecodont in American Heritage Dictionary 4
(thēˈkə-dŏntˌ)
noun
Any of various extinct primitive archosaurs of the order Thecodontia of the late Permian and Triassic periods, having teeth in sockets and probably ancestral to the dinosaurs.