Thecodontosaurus

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Thecodontosaurus
Temporal range: Rhaetian
~203.6–201.3  Ma
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Thecodontosaurus antiquus skeleton.png
Skeletal restoration
Scientific classification OOjs UI icon edit-ltr.svg
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 [1]

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

Contents

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

Size comparison Thecodontosaurus Scale.svg
Size comparison

In the autumn of 1834, surgeon Henry Riley (1797–1848) [2] 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. [3] 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. [4] 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. [5] 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, [6] and in 1908 Friedrich von Huene named a Thecodontosaurus cylindrodon. [7] 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. [8] 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. [9]

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

Misassigned species

Thecodontosaurus caducus was named by Adam Yates in 2003 for a juvenile specimen found in Wales; [14] in 2007 this was made the separate genus Pantydraco . [15] 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. [16]

Description

Life restoration compared to a human Thecondontosaurus life restoration 2018.jpg
Life restoration compared to a human

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. [1]

The small size has been explained as an instance of insular dwarfism. [17]

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. [18] 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, [19] but more recently it has been suggested that Thecodontosaurus and its relatives preceded the prosauropod-sauropod split. [20]

Paleobiology

Reconstruction of limb musculature of Thecodontosaurus Thecodontosaurus antiquus limb musculature.jpg
Reconstruction of limb musculature of Thecodontosaurus

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. [21]

Related Research Articles

<span class="mw-page-title-main">Sauropodomorpha</span> Extinct clade of dinosaurs

Sauropodomorpha is an extinct clade of long-necked, herbivorous, saurischian dinosaurs that includes the sauropods and their ancestral relatives. Sauropods generally grew to very large sizes, had long necks and tails, were quadrupedal, and became the largest animals to ever walk the Earth. The prosauropods, which preceded the sauropods, were smaller and were often able to walk on two legs. The sauropodomorphs were the dominant terrestrial herbivores throughout much of the Mesozoic Era, from their origins in the Late Triassic until their decline and extinction at the end of the Cretaceous.

<i>Plateosaurus</i> Sauropodomorph dinosaur

Plateosaurus is a genus of plateosaurid dinosaur that lived during the Late Triassic period, around 214 to 204 million years ago, in what is now Central and Northern Europe. Plateosaurus is a basal (early) sauropodomorph dinosaur, a so-called "prosauropod". The type species is Plateosaurus trossingensis; before 2019, that honor was given to Plateosaurus engelhardti, but it was ruled as undiagnostic by the ICZN. Currently, there are three valid species; in addition to P. trossingensis, P. longiceps and P. gracilis are also known. However, others have been assigned in the past, and there is no broad consensus on the species taxonomy of plateosaurid dinosaurs. Similarly, there are a plethora of synonyms at the genus level.

<i>Massospondylus</i> Sauropodomorph dinosaur genus from Early Jurassic South Africa and Botswana

Massospondylus was a genus of sauropodomorph dinosaur from the Early Jurassic. It was described by Sir Richard Owen in 1854 from remains discovered in South Africa, and is thus one of the first dinosaurs to have been named. Fossils have since been found at other locations in South Africa, Lesotho, and Zimbabwe. Material from Arizona's Kayenta Formation, India, and Argentina has been assigned to the genus at various times, but the Arizonan and Argentinian material are now assigned to other genera.

Agrosaurus is a potentially dubious genus of thecodontosaurid sauropodomorph probably originating from the Magnesian Conglomerate of England that was originally believed to be a Triassic prosauropod from Australia. Agrosaurus would thus be the oldest dinosaur from that country. However, this appears to have been an error, and the material actually appears to come from Thecodontosaurus or a Thecodontosaurus-like animal from Bristol, England. The type species is Agrosaurus macgillivrayi.

<i>Euskelosaurus</i> Extinct genus of dinosaur from late Triassic southern Africa

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Plateosauravus is a basal plateosaurian of uncertain affinities from the Late Triassic Elliot Formation of South Africa.

<i>Teratosaurus</i> Extinct genus of reptiles

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<i>Palaeosaurus</i> Genus of reptiles (fossil)

Palaeosaurus is a genus of indeterminate archosaur known from two teeth found in the Bromsgrove Sandstone Formation and also either the Magnesian Conglomerate or the Avon Fissure Fill of Clifton, Bristol, England. It has had a convoluted taxonomic history.

Rileyasuchus is a genus of phytosaur from the Rhaetian Magnesian Conglomerate of England. It has a confusing history, being associated with the taxonomy of Palaeosaurus and Thecodontosaurus, and being a replacement name for a preoccupied genus.

Sphenosaurus is a poorly known genus of procolophonid, a type of prehistoric reptile from the Late Permian Buntsanstein of Germany. Originally assigned the name Palaeosaurus sternbergii, by German paleontologist Leopold Joseph Fitzinger in 1840, the generic name was already preoccupied by not one but two other reptiles assigned the name Palaeosaurus. In 1847, Hermann von Meyer recognized the original 1833 and 1836 usages of Palaeosaurus and moved P. sternbergii to a new genus, Sphenosaurus.

<i>Pantydraco</i> An extinct genus of a Dinosaur

Pantydraco is a genus of basal sauropodomorph dinosaur from the Late Triassic of the United Kingdom (Wales). It is based on a partial juvenile skeleton once thought to belong to Thecodontosaurus. Only one valid species of Pantydraco is recognised: P. caducus.

<span class="mw-page-title-main">Thecodontosauridae</span> Extinct family of dinosaurs

Thecodontosauridae is a family of basal sauropodomorph dinosaurs that are part of the Bagualosauria, known from fossil remains found exclusively in the Magnesian Conglomerate of Bristol, England, which dates back to the Rhaetian stage of the Late Triassic. Two genera are known: Agrosaurus and Thecodontosaurus; the former is often considered to be the same animal as the latter.

<span class="mw-page-title-main">Anchisauria</span> Extinct clade of dinosaurs

Anchisauria is an extinct clade of sauropodomorph dinosaurs that lived from the Late Triassic to the Late Cretaceous. The name Anchisauria was first used Haekel and defined by Galton and Upchurch in the second edition of The Dinosauria. It is a node-based taxon containing the most recent common ancestor of Anchisaurus polyzelus and Melanorosaurus readi, and all its descendants. Galton and Upchurch assigned a family of dinosaurs to the Anchisauria: the Melanorosauridae. The more common prosauropods Plateosaurus and Massospondylus were placed in the sister clade Plateosauria.

<span class="mw-page-title-main">Melanorosauridae</span> Extinct family of dinosaurs

The Melanorosauridae were a family of sauropodomorph dinosaurs which lived during the Late Triassic and Early Jurassic. The name Melanorosauridae was first coined by Friedrich von Huene in 1929. Huene assigned several families of dinosaurs to the infraorder "Prosauropoda": the Anchisauridae, the Plateosauridae, the Thecodontosauridae, and the Melanorosauridae. Since then, these families have undergone numerous revisions. Galton and Upchurch (2004) considered Camelotia, Lessemsaurus, and Melanorosaurus members of the family Melanorosauridae. A more recent study by Yates (2007) indicates that the melanorosaurids were instead early sauropods.

<i>Asylosaurus</i> Extinct genus of dinosaurs

Asylosaurus is a genus of basal sauropodomorph dinosaur from the Late Triassic Avon Fissure Fill of England. It is based on partial remains, discovered in the autumn of 1834, described in 1836 by Henry Riley and Samuel Stutchbury as pertaining to Thecodontosaurus, that Othniel Charles Marsh brought to Yale University between 1888 and 1890. These remains thus escaped destruction by a bombardment in 1940 during World War II, unlike the original holotype of Thecodontosaurus. Asylosaurus was described in 2007 by Peter Galton. The type species is A. yalensis, referring to Yale. The bones originally came from a Rhaetian-age cave fill at Durdham Down, Clifton, Bristol.

<span class="mw-page-title-main">Magnesian Conglomerate</span> Geological formation in the United Kingdom

The Magnesian Conglomerate is a geological formation in Clifton, Bristol in England, Gloucestershire and southern Wales, present in Tytherington, Durdham Down, Slickstones Quarry and Cromhall Quarry.

Paleontology or palaeontology is the study of prehistoric life forms on Earth through the examination of plant and animal fossils. This includes the study of body fossils, tracks (ichnites), burrows, cast-off parts, fossilised feces (coprolites), palynomorphs and chemical residues. Because humans have encountered fossils for millennia, paleontology has a long history both before and after becoming formalized as a science. This article records significant discoveries and events related to paleontology that occurred or were published in the year 1836.

The Avon Fissure Fill, also known as the Bristol Fissure Fill or Tytherington Fissure Fill, is a fissure fill in Avon, England which dates variously from the Norian and Rhaetian stages of the Late Triassic, or possibly as late as the Hettangian stage of the Early Jurassic. The fissure fill at Avon was a sinkhole formed by the dissolution of Lower Carboniferous limestones.

References

  1. 1 2 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 Paleontology20(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 Arts28: 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 London47: 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 Supplement57: 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 Museum12: 323–497
  12. S.H. Haughton, 1932, "On a collection of Karroo vertebrates from Tanganyika Territory", Quarterly Journal of the Geological Society of London88(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. Bibcode:2020JVPal..40E0774B. doi: 10.1080/02724634.2020.1770774 . hdl: 1983/01dbc7c5-9473-4057-b164-06cbff0338a4 .
  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. Wikisource-logo.svg  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: 43103
  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): 17538
  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

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