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Thecodontosaurus Temporal range: Rhaetian ~203.6–201.3 Ma PreꞒ Ꞓ O S D C P T J K Pg N ↓
Skeletal restoration
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Clade:	Dinosauria
Clade:	Saurischia
Clade:	†Sauropodomorpha
Family:	†Thecodontosauridae
Genus:	†Thecodontosaurus Riley & Stutchbury, 1836
Type species
†Thecodontosaurus antiquus Morris, 1843
Synonyms
?Agrosaurus Seeley, 1891 ?Pantydraco Galton, Yates & Kermack, 2007

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

Its remains are known mostly from Triassic "fissure fillings" in South England. Thecodontosaurus was a small bipedal animal, about 2 m (6.5 ft) long. It is one of the first dinosaurs to be discovered and is one of the oldest that existed. Many species have been named in the genus, but only the type species Thecodontosaurus antiquus is seen as valid today.

Discovery and naming

Thecodontosaurus antiquus

In the autumn of 1834, surgeon Henry Riley (1797–1848) and the curator of the Bristol Institution, Samuel Stutchbury, began to excavate "saurian remains" at the quarry of Durdham Down, at Clifton, presently a part of Bristol, which is part of the Magnesian Conglomerate. In 1834 and 1835, they briefly reported on the finds. They provided their initial description in 1836, naming a new genus: Thecodontosaurus. The name is derived from Greek θήκή, thēkē, "socket", and οδους, odous, "tooth", a reference to the fact that the roots of the teeth were not fused with the jaw bone, as in present lizards, but positioned in separate tooth sockets. 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. In 1843, in his catalogue of British fossils, John Morris provided a complete species name: Thecodontosaurus antiquus. The specific epithet, "antiquus", means "ancient" in Latin.

The original type specimen or holotype of Thecodontosaurus, BCM 1, a lower jaw, fell victim to heavy World War II bombings. Many remains of this dinosaur and other material related to it were destroyed in November 1940 during the Bristol Blitz. However, most bones were salvaged: today 184 fossil bones are part of the collection of the Bristol City Museum and Art Gallery. Later, more remains were found near Bristol at Tytherington. Currently about 245 fragmentary specimens are known, representing numerous individuals. In 1985, Peter Galton designated another lower jaw, a right dentary, as the neotype, BCM 2. The remains had been found in chalkstone infillings, breccia deposited in fissures in older rocks. The age of these deposits was once estimated as old as the late Carnian, but recent studies indicate that they date from the Rhaetian.

Other species

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 1890, Arthur Smith Woodward accordingly named a Thecodontosaurus platyodon, and in 1908 Friedrich von Huene named a Thecodontosaurus cylindrodon. Though still defended by Michael Cooper in 1981, the hypothesis that such creatures existed has now been totally discredited.

On one occasion, material of Thecodontosaurus was, by mistake, described as a separate genus. 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. 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. In 1906, von Huene had already noted the close resemblance and renamed the species Thecodontosaurus macgillivrayi. It is thus a junior synonym of Thecodontosaurus antiquus.

Presently, the only valid species is thus T. antiquus.

Misassigned species

• Thecodontosaurus latespinatus von Huene, 1907-08 = Tanystropheus
• Thecodontosaurus primus von Huene, 1907-1908 = indeterminate archosauromorph, previously and questionably referred to Protanystropheus
• Thecodontosaurus elizae Sauvage, 1907
• Thecodontosaurus gibbidens Cope, 1878 = Galtonia
• Thecodontosaurus skirtopodus (Seeley, 1894) = Hortalotarsus
• Thecodontosaurus polyzelus (Hitchcock, 1865) von Huene, 1906
• Thecodontosaurus hermannianus von Huene, 1908
• Thecodontosaurus diagnosticus Fraas, 1912 = Efraasia
• Thecodontosaurus minor Haughton, 1918
• Thecodontosaurus dubius Haughton, 1924
• Thecodontosaurus browni (Seeley, 1895) von Huene, 1932
• Thecodontosaurus alophos Haughton, 1932 = Nyasasaurus

Thecodontosaurus caducus was named by Adam Yates in 2003 for a juvenile specimen found in Wales; in 2007 this was made the separate genus Pantydraco. However, Ballell, Rayfield & Benton (2020) considered Pantydraco caducus to be a taxon of uncertain validity, and considered it possible that it might represent a juvenile of Thecodontosaurus antiquus.

Description

From the fragmentary remains of Thecodontosaurus, most of the skeleton can be reconstructed, except for the front of the skull. Thecodontosaurus had a rather short neck supporting a fairly large skull with large eyes. Its jaws contained many small- to medium-sized, serrated, leaf-shaped teeth. This dinosaur's hands and feet each had five digits, and the hands were long and rather narrow, with an extended claw on each. This dinosaur's front limbs were much shorter than the legs, and its tail was much longer than the head, neck and body put together. On average, it was 1.2 metres (3.9 ft) long, 30 centimetres (12 in) or 1 ft. tall, and weighed 11 kilograms (24 lb). The largest individuals had an estimated length of 2.5 metres (8.2 ft).

In 2000, Michael Benton noted the existence of a robust morph in the population, seen by him as a possible second species or, more likely, an instance of sexual dimorphism. 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.

The small size has been explained as an instance of insular dwarfism.

Classification

Riley and Stutchbury originally saw Thecodontosaurus as a member of the Squamata, the group containing lizards and snakes. This did not change when Richard Owen coined the term Dinosauria in 1842, because Owen did not recognise Thecodontosaurus as a dinosaur; in 1865, he assigned it to the Thecodontia. It was not until 1870 that Thomas Huxley became the first person to understand that it was a dinosaur, though referring it incorrectly to the Scelidosauridae. Later, it was placed in either the Anchisauridae or its own Thecodontosauridae alongside Agrosaurus.

Modern exact cladistic analyses have not been conclusive. Although not actually the earliest member of the group, Thecodontosaurus is sometimes placed in a very basal position among the sauropodomorph dinosaurs. It was earlier included under the Prosauropoda, but more recently it has been suggested that Thecodontosaurus and its relatives preceded the prosauropod-sauropod split.

Paleobiology

Examination of Thecodontosaurus revealed it was exclusively bipedal. 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. Its advanced running capabilities suggest it was well adapted for high-speed sprinting, probably as a means of escaping predators.

References

1. ^ M.J. Benton, L. Juul, G.W. Storrs and P.M. Galton, 2000, "Anatomy and systematics of the prosauropod dinosaur Thecodontosaurus antiquus from the upper Triassic of southwest England", Journal of Vertebrate Paleontology 20(1): 77-108
2. Adrian Desmond (15 April 1992). The Politics of Evolution: Morphology, Medicine, and Reform in Radical London. Chicago: University of Chicago Press. p. 427. ISBN 978-0-226-14374-3.
3. Williams, (1835), "Discovery of Saurian Bones in the Magnesian Conglomerate near Bristol", American Journal of Science and Arts 28: 389
4. Riley, H., and Stutchbury, S., (1836), "A description of various fossil remains of three distinct saurian animals discovered in the autumn of 1834, in the Magnesian Conglomerate on Durdham Down, near Bristol", Proceedings of the Geological Society of London 2:397–399
5. Morris, J., 1843, A Catalogue of British Fossils. British Museum, London, 222 pp
6. A.S. Woodward and C.D. Sherborn, 1890, A Catalogue of British Fossil Vertebrat Dulao & Company, London pp. 396
7. F. v. Huene, 1908, "On phytosaurian remains from the Magnesian Conglomerate of Bristol (Rileya platyodon)", Annals and Magazine of Natural History, series 8 1: 228-230
8. Seeley, H.G., 1891, "On Agrosaurus macgillivrayi, a saurischian reptile from the northeast coast of Australia", Quarterly Journal of the Geological Society of London 47: 164–165
9. Vickers-Rich, P., Rich, T.H., McNamara, G.C. & Milner, A. (1999). "Agrosaurus: Australia's oldest dinosaur?". Records of the Western Australian Museum Supplement 57: 191-200
10. Skawiński, T.; Ziegler, M.; Czepiński, Ł.; Szermański, M.; Tałanda, M.; Surmik, D.; Niedźwiedzki, G. (2017). "A re-evaluation of the historical 'dinosaur' remains from the Middle-Upper Triassic of Poland". Historical Biology. 27 (4): 442–472. doi:10.1080/08912963.2016.1188385. S2CID 133166493.
11. Haughton, S.H., 1924, "The fauna and stratigraphy of the Stormberg Series", Annals of the South African Museum 12: 323–497
12. S.H. Haughton, 1932, "On a collection of Karroo vertebrates from Tanganyika Territory", Quarterly Journal of the Geological Society of London 88(4): 634-671
13. Nesbitt, S. J.; Barrett, P. M.; Werning, S.; Sidor, C. A.; Charig, A. J. (2013). "The oldest dinosaur? A Middle Triassic dinosauriform from Tanzania". Biol. Lett. doi:10.1098/rsbl.2012.0949.
14. Yates, A. M. (2003). "A new species of the primitive dinosaur Thecodontosaurus (Saurischia: Sauropodomorpha) and its implications for the systematics of early dinosaurs". Journal of Systematic Palaeontology 1(1): 1-42
15. Galton, P.M., Yates, A.M., & Kermack, D. (2007). "Pantydraco n. gen. for Thecodontosaurus caducus Yates, 2003, a basal sauropodomorph dinosaur from the Upper Triassic or Lower Jurassic of South Wales, UK". Neues Jahrbuch für Geologie und Paläontologie, Abh., 243: 119-125
16. Antonio Ballell; Emily J. Rayfield; Michael J. Benton (2020). "Osteological redescription of the Late Triassic sauropodomorph dinosaur Thecodontosaurus antiquus based on new material from Tytherington, southwestern England". Journal of Vertebrate Paleontology. 4 (2): e1770774. doi:10.1080/02724634.2020.1770774.
17. Whiteside, D.I. and Marshall, J.E.A. (2008) "The age, fauna and palaeoenvironment of the Late Triassic fissure deposits of Tytherington, South Gloucestershire, UK". Geological Magazine, 14(1): 105-147
18.  Huxley, Thomas H. (1870). "On the Classification of the Dinosauria, with observations on the Dinosauria of the Trias". Quarterly Journal of the Geological Society of London. Vol. 26. pp. 32–51. doi:10.1144/gsl.jgs.1870.026.01-02.09 – via Wikisource.
19. Upchurch, P. (1998). "The phylogenetic relationships of sauropod dinosaurs". Zool. J. Linnean Soc. 124: 43–103
20. Yates, A.M. & Kitching, J. W. (2003). "The earliest known sauropod dinosaur and the first steps towards sauropod locomotion". Proc. R. Soc. Lond.: B Biol Sci. 2003 Aug 22; 270(1525): 1753–8
21. Ballell, A.; Rayfield, E.J.; Benton, M.J. (2022). "Walking with early dinosaurs: appendicular myology of the Late Triassic sauropodomorph Thecodontosaurus antiquus". Royal Society Open Science. 9 (1): 211356. Bibcode:2022RSOS....911356B. doi:10.1098/rsos.211356. PMC 8767213. PMID 35116154.

Further reading

• Moody, Richard. Dinofile. Pg. 23. Octopus Publishing Group Ltd., 2006

Data related to Thecodontosaurus at Wikispecies

v t e Sauropodomorpha
Kingdom: Animalia Phylum: Chordata Class: Sauropsida Clade: Avemetatarsalia Clade: Dinosauria Avemetatarsalia see Avemetatarsalia Sauropodomorpha see below↓
Sauropodomorpha Sauropodomorpha Buriolestes Eoraptor Gigantoscelus Guaibasaurus Mbiresaurus Pampadromaeus Panphagia Saturnaliidae Buriolestes? Eoraptor? Chromogisaurus Nhandumirim Pampadromaeus? Panphagia? Saturnalia Bagualosauria Arcusaurus Asylosaurus Bagualosaurus Efraasia Nambalia Pantydraco Thecodontosaurus Unaysauridae Jaklapallisaurus Macrocollum Unaysaurus Plateosauria Plateosauravus Ruehleia Xixiposaurus Plateosauridae Euskelosaurus Gresslyosaurus Issi Pachysauriscus Plateosaurus Yimenosaurus Massopoda Gryponyx Gyposaurus Ignavusaurus Kholumolumo Musankwa Sarahsaurus Tuebingosaurus Riojasauridae Eucnemesaurus Riojasaurus Massospondylidae Adeopapposaurus Coloradisaurus Glacialisaurus Ignavusaurus? Leyesaurus Lufengosaurus Massospondylus Ngwevu Pradhania Sarahsaurus Xingxiulong? Sauropodiformes Chuxiongosaurus? Jingshanosaurus Lishulong Qianlong Seitaad Xingxiulong? Yizhousaurus Yunnanosaurus Anchisauria Aardonyx Anchisaurus Camelotia Irisosaurus Lamplughsaura Leonerasaurus Melanorosaurus Meroktenos Mussaurus Pulanesaura Sefapanosaurus Sauropoda see below↓
Sauropoda Sauropoda Amygdalodon Blikanasaurus Chinshakiangosaurus Gongxianosaurus Isanosaurus Leonerasaurus? Pulanesaura? Protognathosaurus Schleitheimia Tuebingosaurus? Lessemsauridae Antetonitrus Ingentia Ledumahadi Lessemsaurus Gravisauria Archaeodontosaurus? Kotasaurus Ohmdenosaurus Rhoetosaurus Sanpasaurus? Zizhongosaurus? Vulcanodontidae Tazoudasaurus Vulcanodon Eusauropoda Algoasaurus Asiatosaurus Bagualia Barapasaurus Bellusaurus Cetiosauriscus Dashanpusaurus Dystrophaeus Janenschia Jobaria Nebulasaurus Perijasaurus Shunosaurus Spinophorosaurus Tehuelchesaurus Volkheimeria Cetiosauridae Cetiosaurus Chebsaurus Ferganasaurus? Lapparentosaurus? Patagosaurus? Mamenchisauridae Analong Anhuilong Cetiosauriscus? Chuanjiesaurus Datousaurus? Eomamenchisaurus Huangshanlong Hudiesaurus Jingiella Klamelisaurus? Mamenchisaurus Omeisaurus Qijianglong Rhomaleopakhus Tienshanosaurus Tonganosaurus Wamweracaudia Xinjiangtitan Yuanmousaurus Zigongosaurus Turiasauria Amanzia Bellusaurus? Haestasaurus? Janenschia? Losillasaurus Mierasaurus Moabosaurus Narindasaurus Oplosaurus? Tehuelchesaurus? Tendaguria Turiasaurus Zby Neosauropoda Diplodocoidea (see below ↓ ) Macronaria (see below ↓ ) Dubious sauropods Bothriospondylus Cardiodon Dinodocus Gigantosaurus Neosodon Qinlingosaurus Ultrasaurus
Diplodocoidea Diplodocoidea Haplocanthosaurus Diplodocimorpha Rebbachisauridae Agustinia Amazonsaurus Campananeyen Comahuesaurus Dzharatitanis? Histriasaurus Lavocatisaurus Maraapunisaurus? Nopcsaspondylus Sidersaura Xenoposeidon Zapalasaurus Khebbashia Limaysaurinae Cathartesaura Limaysaurus Rayososaurus? Rebbachisaurinae Demandasaurus Itapeuasaurus Katepensaurus Nigersaurus Rebbachisaurus Tataouinea Flagellicaudata Dicraeosauridae Amargasaurus Amargatitanis Bajadasaurus Brachytrachelopan Dicraeosaurus Dyslocosaurus? Kaatedocus Lingwulong Pilmatueia Smitanosaurus Suuwassea Tharosaurus Diplodocidae Apatosaurinae Amphicoelias? Apatosaurus Atlantosaurus? Brontosaurus Diplodocinae Ardetosaurus Barosaurus Dinheirosaurus Diplodocus Galeamopus Kaatedocus? Leinkupal Supersaurus Tornieria
Macronaria Macronaria Abrosaurus Aragosaurus Bashunosaurus? Daanosaurus Dashanpusaurus? Europasaurus Haestasaurus? Yuzhoulong Camarasauridae Camarasaurus Lourinhasaurus Titanosauriformes Astrodon Duriatitan Eucamerotus Fushanosaurus Fusuisaurus Ornithopsis Pelorosaurus Rugocaudia? Brachiosauridae Abydosaurus Atlasaurus Brachiosaurus Cedarosaurus Galvesaurus? Giraffatitan Lusotitan Sonorasaurus Soriatitan Venenosaurus Vouivria Somphospondyli Angolatitan Arkharavia Astrophocaudia Austrosaurus Brohisaurus Brontomerus Chubutisaurus Dongbeititan Europatitan Fukuititan Garumbatitan Jiangxititan? Jiutaisaurus Liaoningotitan Ligabuesaurus? Liubangosaurus Oceanotitan Padillasaurus Pukyongosaurus Ruixinia Sauroposeidon Sibirotitan Tastavinsaurus Triunfosaurus Euhelopodidae Australodocus? Chiayusaurus? Erketu Euhelopus Gannansaurus Gobititan Huabeisaurus Huanghetitan Jiangshanosaurus? Phuwiangosaurus Qiaowanlong Silutitan Tambatitanis Tangvayosaurus Yongjinglong Yunmenglong Diamantinasauria Australotitan Diamantinasaurus Sarmientosaurus Savannasaurus Wintonotitan? Titanosauria see below↓
Titanosauria Titanosauria Abdarainurus Aegyptosaurus? Andesaurus Angolatitan? Arackar Argyrosaurus Atacamatitan Austroposeidon Baotianmansaurus Barrosasaurus Baurutitan? Bonatitan? Borealosaurus Brasilotitan Choconsaurus Daxiatitan Dongyangosaurus Dreadnoughtus? Elaltitan Epachthosaurus? Gandititan Hamititan Huabeisaurus Jiangshanosaurus? Kaijutitan Karongasaurus Laplatasaurus Ligabuesaurus? Magyarosaurus Malarguesaurus? Malawisaurus Mnyamawamtuka Narambuenatitan Ninjatitan Normanniasaurus Nullotitan Pellegrinisaurus? Petrobrasaurus Pitekunsaurus Rapetosaurus Rukwatitan Ruyangosaurus Tastavinsaurus? Tengrisaurus? Tiamat Traukutitan Trigonosaurus Sonidosaurus Uberabatitan Volgatitan Xianshanosaurus Diamantinasauria? Lirainosaurinae Ampelosaurus Atsinganosaurus Garrigatitan Lirainosaurus Lohuecotitan Mansourasaurus Paludititan Eutitanosauria Inawentu Menucocelsior Colossosauria Antarctosaurus Baalsaurus Bonitasaura Chucarosaurus Epachthosaurus? Jainosaurus Quetecsaurus Tengrisaurus? Vahiny Rinconsauria Adamantisaurus Maxakalisaurus? Muyelensaurus Overosaurus Panamericansaurus Rinconsaurus Aeolosaurini Aeolosaurus Arrudatitan Bravasaurus Caieiria Gondwanatitan Punatitan Shingopana Lognkosauria Argentinosaurus Drusilasaura Dzharatitanis? Futalognkosaurus Jiangxititan? Mendozasaurus Notocolossus Patagotitan Puertasaurus Saltasauroidea Bustingorrytitan Titanomachya Udelartitan Nemegtosauridae Nemegtosaurus Quaesitosaurus? Tapuiasaurus? Saltasauridae Igai Isisaurus? Qingxiusaurus Quaesitosaurus? Opisthocoelicaudiinae Abditosaurus? Alamosaurus Baurutitan? Dreadnoughtus? Opisthocoelicaudia Pellegrinisaurus? Qunkasaura Zhuchengtitan? Saltasaurinae Abditosaurus? Bonatitan? Ibirania Maxakalisaurus? Neuquensaurus Paralititan Rocasaurus Saltasaurus Yamanasaurus Dubious titanosaurs Bruhathkayosaurus? Campylodoniscus Clasmodosaurus Hypselosaurus Iuticosaurus Loricosaurus Macrurosaurus? Microcoelus Mongolosaurus? Titanosaurus
Topics in sauropodomorph research Sauropod neck posture Sauropod hiatus List of sauropod species

• Sauropodomorphs
• Rhaetian life
• Late Triassic dinosaurs of Europe
• Triassic England
• Fossils of England
• Fossils of Serbia
• Fossil taxa described in 1836
• Taxa named by Samuel Stutchbury