Thecodontosaurus ("socket-tooth lizard") is a genus of herbivorous basal sauropodomorph dinosaur that lived during the late Triassic period (Carnian?

[5] Thecodontosaurus was the fifth dinosaur named, after Megalosaurus, Iguanodon, Streptospondylus and Hylaeosaurus, though Riley and Stutchbury were not aware of this, the very concept of Dinosauria only being created in 1842.

The original type specimen or holotype of Thecodontosaurus, BCM 1, a lower jaw, fell victim to heavy World War II bombings.

Apart from the original type species, Thecodontosaurus antiquus, Riley and Stutchbury also found some teeth of carnivorous phytosaurians that they named Palaeosaurus cylindrodon and P. platyodon.

In the late nineteenth century, the theory became popular that such remains belonged to carnivorous prosauropods: animals with the body of Thecodontosaurus, but with slicing teeth.

In 1891, Harry Govier Seeley named Agrosaurus macgillivrayi, assuming the remains had been collected in 1844 by the crew of HMS Fly on the northeast coast of Australia.

[9] It was long considered the first dinosaur found in Australia, but in 1999 it was discovered that the bones probably belonged to a lot sent by Riley and Stutchbury to the British Museum of Natural History and then mislabelled.

Thecodontosaurus caducus was named by Adam Yates in 2003 for a juvenile specimen found in Wales;[15] in 2007 this was made the separate genus Pantydraco.

Benton also indicated some unique derived traits, or autapomorphies, for the species: a long basipterygoid process on the braincase; a dentary that is short in relation to the total length of the lower jaw; an ilium that has a back end that is subquadrate instead of rounded.

Studies of the muscle attachments in its fore and hindlimbs suggest that it was an extremely fast bipedal runner that relied on its weaker front limbs for grasping vegetation, cutting it up and feeding it into its mouth.