| Thecodontosaurus | |
|---|---|
 | |
| Skeletal restoration | |
Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Clade: | Dinosauria |
| Clade: | Saurischia |
| Clade: | †Sauropodomorpha |
| Family: | †Thecodontosauridae |
| Genus: | †Thecodontosaurus Riley &Stutchbury, 1836 |
| Type species | |
| †Thecodontosaurus antiquus Morris, 1843 | |
| Synonyms[1] | |
| |
Thecodontosaurus ("socket-tooth lizard") is agenus ofherbivorous basalsauropodomorphdinosaur that lived during the lateTriassic period (Carnian age).[2] Its remains are known mostly from Triassic "fissure fillings" in southernEngland.Thecodontosaurus was a small bipedal animal, about 2 m (6.6 ft) long. It is one of the first dinosaurs to be discovered and is one of the oldest that ever existed. Many species have been named within the genus, but only thetype speciesThecodontosaurus antiquus is seen as valid today.
In the autumn of 1834,surgeonHenry Riley (1797–1848)[3] and thecurator of theBristol Institution,Samuel Stutchbury, began to excavate "saurian remains" at the quarry ofDurdham Down, atClifton, presently a part ofBristol, which is part of theMagnesian Conglomerate. In 1834 and 1835, they briefly reported on the finds.[4] 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.[5]Thecodontosaurus was the fifth dinosaur named, afterMegalosaurus,Iguanodon,Streptospondylus andHylaeosaurus, though Riley and Stutchbury were not aware of this, the very concept ofDinosauria only being created in 1842. In 1843, in his catalogue of British fossils,John Morris provided a completespecies name:Thecodontosaurus antiquus.[6] Thespecific epithet,"antiquus", means "ancient" inLatin.
The originaltype specimen orholotype ofThecodontosaurus, BCM 1, a lower jaw, fell victim to heavyWorld War II bombings. Many remains of this dinosaur and other material related to it were destroyed in November 1940 during theBristol Blitz. However, most bones were salvaged: today 184 fossil bones are part of the collection of theBristol City Museum and Art Gallery. Later, more remains were found nearBristol atTytherington. Currently about 245 fragmentary specimens are known, representing numerous individuals. In 1985,Peter Galton designated another lower jaw, a right dentary, as theneotype, BCM 2. The remains had been found inchalkstone infillings,breccia deposited in fissures in older rocks. The age of these deposits was once estimated as old as the lateCarnian, but recent studies indicate that they date from theRhaetian.
Apart from the originaltype species,Thecodontosaurus antiquus, Riley and Stutchbury also found some teeth of carnivorousphytosaurians that they namedPalaeosaurus cylindrodon andP. platyodon. In the late nineteenth century, the theory became popular that such remains belonged to carnivorousprosauropods: animals with the body ofThecodontosaurus, but with slicing teeth. In 1890,Arthur Smith Woodward accordingly named aThecodontosaurus platyodon,[7] and in 1908Friedrich von Huene named aThecodontosaurus cylindrodon.[8] Though still defended by Michael Cooper in 1981, the hypothesis that such creatures existed has now been totally discredited.
On one occasion, material ofThecodontosaurus was, by mistake, described as a separate genus. In 1891,Harry Govier Seeley namedAgrosaurus macgillivrayi, assuming the remains had been collected in 1844 by the crew ofHMSFly on the northeast coast ofAustralia.[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 theBritish Museum of Natural History and then mislabelled. In 1906, von Huene had already noted the close resemblance and renamed the speciesThecodontosaurus macgillivrayi. It is thus ajunior synonym ofThecodontosaurus antiquus.[10]
Presently, the only valid species is thusT. antiquus.
Thecodontosaurus caducus was named byAdam Yates in 2003 for a juvenile specimen found inWales;[15] in 2007 this was made the separate genusPantydraco.[16] However, Ballell, Rayfield & Benton (2020) consideredPantydraco caducus to be a taxon of uncertain validity, and considered it possible that it might represent a juvenile ofThecodontosaurus antiquus.[17]
From the fragmentary remains ofThecodontosaurus, 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 robustmorph in the population, seen by him as a possible second species or, more likely, an instance ofsexual dimorphism. Benton also indicated some unique derived traits, orautapomorphies, for the species: a longbasipterygoid process on thebraincase; a dentary that is short in relation to the total length of the lower jaw; anilium that has a back end that is subquadrate instead of rounded.[1]
The small size has been explained as an instance ofinsular dwarfism.[18]
Riley and Stutchbury originally sawThecodontosaurus as a member of theSquamata, the group containing lizards and snakes. This did not change whenRichard Owen coined the term Dinosauria in 1842, because Owen did not recogniseThecodontosaurus as a dinosaur; in 1865, he assigned it to theThecodontia. It was not until 1870 thatThomas Huxley became the first person to understand that it was a dinosaur, though referring it incorrectly to theScelidosauridae.[19] Later, it was placed in either theAnchisauridae or its ownThecodontosauridae alongsideAgrosaurus.
Modern exactcladistic analyses have not been conclusive. Although not actually the earliest member of the group,Thecodontosaurus is sometimes placed in a very basal position among thesauropodomorph dinosaurs. It was earlier included under theProsauropoda,[20] but more recently it has been suggested thatThecodontosaurus and its relatives preceded the prosauropod-sauropod split.[21]
Examination ofThecodontosaurus 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.[22]
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 – viaWikisource.
Data related toThecodontosaurus at Wikispecies
