‘Tooth-in-socket’ reptiles, and the most primitive order of the Archosauria (‘ruling reptiles’), ranging from the Upper Permian to the Upper Triassic. They were ancestral to the dinosaurs, pterosaurs, and crocodiles. One of the first thecodonts was Thecodontosaurus browni which flourished during the Early Triassic. It grew to 2–3 m in length and had a small head and neck. Essentially it was a quadruped, but it could walk on its hind legs.