Thecodont ('socket-toothed' reptile), is a catch-all group, now considered an obsolete term, that was formerly used to describe a group of the earliest archosaurs that lived during the Permian and Triassic periods.
The 'Thecodonts' are not now considered monophyletic, that is, descended from a single ancestor. The group included ancestors of dinosaurs, (including birds), and of pterosaurs, and crocodilians, groups that diverged during the early Triassic.
Thecodontosaurus was a very early (late Triassic) dinosaur (after which the so-called 'Thecodonts' were named) Thecodontosaurus was a herbivore, about 7 feet (2.1 meters) long. It had a small head on a relatively short neck, long legs and short arms with large thumb claws, and a long tail for balance. It could probably walk on two or four legs, perhaps grazing and walking on all fours, but running on two legs. It had blunt teeth with serrated edges. It had four toes on each leg and five fingers on each hand. Fossil Thecodontosaurus have been found in Britain, which was probably dry and desert-like during the late Triassic. Thecodontosaurus is classified as a saurischian ("lizard-hipped") dinosaur, a sauropodomorph (usually quadrupedal herbivores), a prosauropod (an early, dead-end branch of the sauropodamorpha), and an Archisaurid (the earliest prosauropods.)
