Thecodontosaurus

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.

Thecodontosaurus
Temporal range:
Rhaetian, Late Triassic 203.6–201.3 Ma
Thecodontosaurus antiquus skeleton
Skeletal restoration
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Clade: Dinosauria
Order: Saurischia
Suborder: Sauropodomorpha
Family: Thecodontosauridae
Lydekker, 1890
Genus: Thecodontosaurus
Riley & Stutchbury, 1836
Type species
Thecodontosaurus antiquus
Morris, 1843
Synonyms[1]

?Agrosaurus Seeley, 1891

Discovery and naming

Thecodontosaurus antiquus

Thecodontosaurus Scale
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. 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 by the Germans. 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 latespinatus von Huene, 1907-08 = Tanystropheus
  • Thecodontosaurus primus von Huene, 1907-1908 = 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[10]
  • Thecodontosaurus browni (Seeley 1895) von Huene 1932
  • Thecodontosaurus alophos Haughton 1932 = Nyasasaurus[11][12]

Thecodontosaurus caducus was named by Adam Yates in 2003 for a juvenile specimen found in Wales;[13] in 2007 this was made the separate genus Pantydraco.[14]

Description

Thecodontosaurus
Restoration

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.[15]

Phylogeny

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.[16] Later, it was be placed in either the Anchisauridae or its own Thecodontosauridae.

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,[17] but more recently it has been suggested that Thecodontosaurus and its relatives preceded the prosauropod-sauropod split.[18] New reconstructions show that its neck is proportionally shorter than those in more advanced early sauropodomorphs.

The Bristol Dinosaur Project

Bob Nicholls
Bob Nicholls sculpting a model in Bristol Museum

Thecodontosaurus has formed the basis of a massive public engagement exercise, the Bristol Dinosaur Project, that has run since 2000. In 2009, HLF core funded the Bristol Dinosaur Project, which allowed for the hiring of an Educational Officer and a Fossil Preparator to further develop the project. This funding resulted in three and a half years of extensive laboratory, research, and outreach work that presented the project to thousands of people all around the world.

Notes

  1. ^ a b 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. ^ Anonymous, 1835, "Discovery of Saurian Bones in the Magnesian Conglomerate near Bristol", American Journal of Science and Arts 28: 389
  4. ^ Riley, H., and S. Stutchbury, 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. ^ Haughton, S.H., 1924, "The fauna and stratigraphy of the Stormberg Series", Annals of the South African Museum 12: 323–497
  11. ^ 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
  12. ^ 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.
  13. ^ 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
  14. ^ 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
  15. ^ 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
  16. ^ Huxley, T. H. 1870. "On the classification of the Dinosauria, with observations on the Dinosauria of the Trias". Quarterly Journal of the Geological Society of London 26: 32–50
  17. ^ Upchurch, P. (1998). "The phylogenetic relationships of sauropod dinosaurs". Zool. J. Linnean Soc. 124: 43–103
  18. ^ 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

References

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

External links

1836 in paleontology

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.

Agrosaurus

Agrosaurus (; Greek agros meaning 'field' and sauros meaning 'lizard', "field lizard") is the name given to the remains of what 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.

Members of an expedition from the British sloop HMS Fly supposedly collected a tibia, a claw and some other fragments in 1844 from Cape York, Queensland. The original block was purchased by the British Museum of Natural History in 1879, but the remains were not studied until 1891. Harry Govier Seeley in that year named it Agrosaurus macgillivrayi. The block was prepared in the late 1980s. Following the preparation, Ralph Molnar (1991) noticed similarities to the prosauropod Massospondylus. Galton and Cluver (1976) saw Agrosaurus as close to Anchisaurus. Vickers-Rich, Rich, McNamara and Milner (1999) equated Agrosaurus and Thecodontosaurus antiquus, claiming that the British Museum remains were mislabelled. The difficulty in correctly identifying the source of the fossil lies in the fact that the log of the Fly does not record it. The matrix in which the prosauropod bones were preserved was tested with rocks of similar age in Cape York and Durdham Downs, the latter being beds where Thecodontosaurus remains have been found in the Bristol area of England. The English beds compared most favourably. In fact, as early as 1906 Friedrich von Huene had described the rock matrix as 'extremely reminiscent of the bone breccia at Durdham Downs near Bristol' and had renamed the species Thecodontosaurus macgillivrayi. Remains of the jaw of a sphenodont identical to Diphyodontosaurus avonis, a lizard-like reptile common to the Bristol Triassic beds have been extracted. This reinterpretation of Agrosaurus as a misidentified British specimen has been accepted in later works.From the scant remains the living animal would appear to have been about three metres long (10 ft), with a typically prosauropodan appearance: bulky body, long neck, small head and clawed feet. Like other prosauropods, it was probably equally comfortable on all fours as well as on its elongated hind legs. It was herbivorous or may have been an omnivore.

The name Agrosaurus is now generally considered to be a nomen dubium or a junior synonym of Thecodontosaurus. If Agrosaurus is not from Australia, which seems most probable, Rhoetosaurus and Ozraptor, both from the Bajocian (Middle Jurassic) would be the oldest known Australian dinosaurs. They are well documented.

Ankistrodon

Ankistrodon is an extinct genus of archosauriform known from the Early Triassic Panchet Formation of India. First thought to be a theropod dinosaur, it was later determined to be a proterosuchid. The type species is A. indicus, described by prolific British zoologist Thomas Henry Huxley in 1865. One authority in the 1970s classified Ankistrodon as a senior synonym of Proterosuchus.

Asylosaurus

Asylosaurus (meaning "unharmed or sanctuary lizard") is a genus of basal sauropodomorph dinosaur from the Late Triassic of England. It is based on partial remains, 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.Asylosaurus is based on YPM 2195, a partial skeleton of the torso region, including back vertebrae, ribs, gastralia, a shoulder girdle, humeri, a partial forearm, and a hand; additional bones from the neck, tail, pelvis, arm and leg that may represent the same individual were also referred to Asylosaurus. It differs from Thecodontosaurus and Pantydraco, contemporaneous basal sauropodomorphs of similar builds, in the structure of its humerus (upper arm). It may have had a separate ecological niche from these other related animals based on how omnivorous or herbivorous it was. According to Gregory S. Paul, it was 2 metres (6 ft 7 in) long and its weight was about 25 kilograms (55 lb).

Chuxiongosaurus

Chuxiongosaurus is a genus of basal sauropodomorph dinosaur which lived during the Early Jurassic Period. Fossils of this genus have been found in the Lower Lufeng Formation, Yunnan Province, southern China. Identified from the holotype CMY LT9401 a nearly complete skull (including a lower jaw) with some similarities to Thecodontosaurus, it was described as the "first basal sauropod dinosaur from the Early Jurassic of China," more basal than Anchisaurus. It was named by Lü Junchang, Yoshitsugu Kobayashi, Li Tianguang and Zhong Shimin in 2010, and the type species is Chuxiongosaurus lufengensis.

Efraasia

Efraasia (pronounced "E-FRAHS-ee-A") is a genus of basal sauropodomorph dinosaur. It was a herbivore which lived during the middle Norian stage of the Late Triassic, around 210 million years ago, in what is now Germany. It was named in 1973 after Eberhard Fraas, who during the early twentieth century collected what were the original type specimens.

The specimens were at first assigned to three already existing genera and so became divided among three separate species: Teratosaurus minor, Sellosaurus fraasi and Paleosaurus diagnosticus. In 2003 these were combined into a single valid species: Efraasia minor.

Efraasia was a lightly built, medium-sized sauropodomorph, about 6 to 7 metres (20 to 23 ft) long.

Galtonia gibbidens

Galtonia is the name given to a genus of pseudosuchian from the Late Triassic. Its fossils were found in Pennsylvania and were originally described by Edward Drinker Cope in 1878.

The type species, Galtonia gibbidens, was originally classified as Thecodontosaurus gibbidens, but was moved to a new genus by Hunt and Lucas in 1994. There is also a genus of flower with the name Galtonia, causing further confusion.

Henry Riley

Henry Riley or Henry Reilly may refer to:

Henry Riley (paleontologist) (1797–1848), British surgeon and naturalist, co-discovered the Thecodontosaurus

Henry Thomas Riley (1816–1878), English translator, lexicographer, and antiquary

Henry Chauncey Riley (1835–1904), missionary bishop

Henry Reilly, Northern Irish politician

Henry J. Reilly (1881–1963), American soldier and journalist

Holwell Quarries

Holwell Quarries (grid reference ST726450) is a 1.3 hectare geological Site of Special Scientific Interest at Holwell near Nunney on the Mendip Hills in Somerset, notified in 1952.

Holwell Quarries represent an internationally important geological locality. A comprehensive assemblage of Triassic (including Rhaetic), Lower Jurassic and Middle Jurassic fissure fillings are well displayed. The Rhaetic fissure fillings have yielded the richest assemblage of vertebrate faunas known from the British Triassic. Fissure deposits have also yielded 8 or 9 genera of Reptiles: a Crocodilian, a Placodont (the first record in Britain of this sub-order), and the dinosaurs Thecodontosaurus and Palaeosaurus. The Lower Jurassic fissure fillings yield ammonites and brachiopods which are important in dating these deposits.

Magnesian Conglomerate

The Magnesian Conglomerate is a geological formation in England. It dates back to the "Norian-Rhaetian".

Nambalia

Nambalia is a genus of basal sauropodomorph dinosaur. It lived during the Late Triassic period (late Norian to earliest Rhaetian) in what is now Andhra Pradesh, central India. It is known from the holotype ISI R273, parts 1-3, partially articulated postcranial material and from the paratypes ISI R273, parts 4-29, including partial postcrania of at least two individuals of different sizes found closely associated and one of them is nearly the same size as the

holotype. ISI R273 was discovered and collected from the Upper Maleri Formation within the Pranhita–Godavari Basin,

north of Nambal village. It was first named by Fernando E. Novas, Martin D. Ezcurra, Sankar Chatterjee and T. S. Kutty in 2011 and the type species is Nambalia roychowdhurii. The generic name is derived from the Indian village of Nambal which is close to the type locality. The specific name honors Dr. Roy Chowdhuri, for his research on the Triassic vertebrate faunas of India. A cladistic analysis by Novas et al. found that Nambalia is basal to Efraasia, Plateosauravus, Ruehleia and Plateosauria, but more derived than Thecodontosaurus, Pantydraco, and Guaibasauridae. Nambalia was found along with the plateosaurid Jaklapallisaurus, a guaibasaurid, and two basal dinosauriforms.

Norian

The Norian is a division of the Triassic geological period. It has the rank of an age (geochronology) or stage (chronostratigraphy). The Norian lasted from ~227 to 208.5 million years ago. It was preceded by the Carnian and succeeded by the Rhaetian.

Palaeosaurus

Palaeosaurus (or Paleosaurus) is a genus of indeterminate archosaur from the Magnesian Conglomerate of Bristol, England. It has had a convoluted taxonomic history.

Richard Owen's mistake of associating prosauropod skeletal remains with the carnivorous teeth which Riley and Stutchbury called Palaeosaurus, combined with von Huene's Teratosaurus minor, which was also a combination of carnivore and prosauropod remains, led paleontologists to view prosauropods as carnivorous animals for quite a long time. This error made it into several textbooks and other dinosaur reference works.

Pantydraco

Pantydraco (where "panty-" is short for Pant-y-ffynnon, signifying hollow of the spring/well in Welsh, referring to the quarry at Bonvilston in South Wales where it was found) was a genus of basal sauropodomorph dinosaur from the Late Triassic of the United Kingdom. It is based on a partial juvenile skeleton once thought to belong to Thecodontosaurus. Only one valid species of Pantydraco is recognised: P. caducus.

Quarry Steps, Durdham Down

Quarry Steps, Durdham Down (grid reference ST573747) is a 0.006 hectare geological Site of Special Scientific Interest near Durdham Down in Bristol, notified in 1990.

It was in this area that the first Thecodontosaurus fossil was discovered in 1834.

Rileyasuchus

Rileyasuchus (meaning "Riley’s crocodile") is a genus of phytosaur from the Rhaetian (Late Triassic) 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 (Rileya, which had already been used by Howard (or Ashmead; it's unclear which one has priority, but they apparently are the same animal) in 1888 for a hymenopteran).

Samuel Stutchbury

Samuel Stutchbury (15 January 1798 – 12 February 1859) was an English naturalist and geologist. He was co-discoverer of Thecodontosaurus, which in 1836 was the fourth dinosaur genus to be named. He also played a part in Gideon Mantell's naming of Iguanodon. As a geological surveyor he mapped a large area of eastern Australia.

Sauropodomorpha

Sauropodomorpha ( SOR-ə-POD-ə-MOR-fə; from Greek, meaning "lizard-footed forms") 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 mid-Triassic (approximately 230 Ma) until their decline and extinction at the end of the Cretaceous (approximately 66 Ma).

Unaysauridae

Unaysauridae is a family of basal sauropodomorphs from the Late Triassic of India and Brazil.

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