Thecodontosaurus

*Thecodontosaurus* is an extinct genus of sauropodomoroph that lived in England during the Late Triassic.

## History

Henery Riley (autumn 1834) excavated "saurian remains" from the Durdham Down quarry at Clifton, Bristol. In 1834-35, they briefly reported on the finds but were formally described in 1836, where *Thecodontosaurus* (from the Greek θήκή, thēkē, meaning "socket", and οδους, odous, meaning "tooth"; this was based on how the tooth roots were not fused to the jaw). This would make it the fifth dinosaur named after the original trio and *Streptospondylus*, though Riley and Stuchbury were unaware of this since the term would be named in 6 years time. John Morris (1843) used his catalogue of British fossils to provide a full binomial name: *T. antiquus*, with the specific epithet meaning "ancient" in Latin. The holotype, BCM 1, a lower jaw, was destroyed by WWII bombings, like many other remains like it during the November 1940 Bristol Blitz. However, 184 fossils were recovered and are now in the Bristol City Museum and Art Gallery. Additional remains were discovered near Tytherington, with about 245 fragments from many individuals being known today. Peter Galton (1985) designated a right dentary, BCM 2, as the neotype. The remains were discovered in chalkstone infillings, which were once attributed to the Late Carnian but are now known to be of the Rhaetian. It has become a mascot for massive public engagement in the Bristol Dinosaur Project (2000 and onwards), which funded job hiring in 2009 and funded 3.5 years of extensive lab research and science communication.

## Description

Most of the skeleton is able to be reconstructed based on fragmentary remains except for the front of the skull. Otherwise, the skull was fairly large as were the eyes and the neck was rather short. The teeth were small-to-medium-sized serrated, leaf-shaped teeth. It has five digits on the hands and feet, with the former being long and narrow with an extended claw on each. The front limbs were much shorter and the tail was much longer than the neck and body. The largest individuals are estimated to eb 2.5 meters (8.2 feet) long. Michael Benton (2000) noted a robust morph that he believed could be a second species or (more likely) a form of sexual dimorphism. Benton also noted some autapomorphies, such as a long blasipterygoid process on the braincase, a dentary that is shorter compared to the total mandibular length and an ilium that is subquadrate at the rear rather than rounded. It's small size has been attributed to insular dwarfism.

## Classification

Riley and Stutchbury assigned the genus to Squamata, which did not change upon the coining of Dinosauria and was later assigned to Thecodontia in 1865. In 1870, Thomas Huxley understood that it was a dinosaur and referred it to Scelidosauridae. It was later placed in Anchisauridae and then Thecodontosauridae with *Agrosaurus*. It is sometimes placed in a very basal position despite not being the earliest genus of this group due to inconclusive phylogenetic testing. It was once a part of Prosauropoda but is now understood to proceed the sauropodomorph-sauropod split.

## Paleobiology

Biomechanics suggests that it was a fast bipedal runner that relied on its weaker front limbs to grasp vegetation before processing it in its mouth. It was likely well-adapted for advanced running and high-speed running to escape predators.

## Species

### Reassigned Species

* *T. latespinatus*
* *T. primus* (=Archosauria indet., =*Protanystropheus*?)
* *T. gibbidens*
* *T. skirtopodus*
* *T. diagnosticus*
* *T. alophos*
* *T. platyodon* and *cylindrodon*
* *T. macgillivrayi*

## Synonyms

* *T. elizae*
* *T. polyzelus*
* *T. hermannianus*
* *T. minor*
* *T. dubius*
* *T. browni*
* *T. caducus* (=juvenile, =*Pantydraco*, =juvenile)
* *Agrosaurus*?
* *Pantydraco*?

## References

https://en.wikipedia.org/wiki/Thecodontosaurus