Thecodontosaurus
Encyclopedia
Thecodontosaurus is a genus
of herbivorous
basal sauropodomorph dinosaur
which lived during the late Triassic period
(Norian
and/or 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 that were discovered and one of the oldest that existed. Many species have been named in the genus but only the type species
Thecondontosaurus antiquus is seen as valid today.
Henry Riley and 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. They provided their initial description in 1836, naming a new genus: Thecodontosaurus. The name is derived from Greek thekè, "socket", and 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 Dinosauria only being created in 1842. In 1843 John Morris
in his catalogue of British fossils provides 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 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: 184 are today part of the collection of the Bristol City Museum and Art Gallery
. Also, later some more remains were found near Bristol
at Tytherington
. At present in total 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 have 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
.
, Thecodontosaurus antiquus, seventeen other species would be named in the genus.
Riley and Stutchbury also found some teeth of carnivorous phytosaurians that they named Paleosaurus cylindrodon and P. platyodon. In the late nineteenth century the theory became popular that such remains would have belonged to carnivorous prosauropods: animals with the body of Thecodontosaurus but with heads armed with slicing teeth. In 1890 Arthur Smith Woodward
accordingly named a Thecodontosaurus platyodon, in 1908 Friedrich von Huene
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 transpired that the bones probably belonged to a lot sent by Riley and Stutchbury to the British Museum of Natural History and then mislabelled. Already in 1906 von Huene had noted the close resemblance and renamed the species Thecodontosaurus macgillivrayi. It is thus a junior synonym of Thecodontosaurus antiquus.
It also happened that remains of completely different animal groups were referred to Thecodontosaurus. Thecodontosaurus latespinatus and Thecodontosaurus primus, both named by von Huene in 1905, were based on material from Tanystropheus
. In 1908 von Huene tentatively renamed Plateosaurus
elizae Sauvage 1907 into Thecodontosaurus? elizae; it is a nomen dubium
based on theropod remains. The proterosuchid Ankistrodon
Huxley 1865 was renamed Thecodontosaurus indicus.
A larger category consists of related basal sauropodomorphs assigned to Thecodontosaurus. These include in chronological order: Thecodontosaurus gibbidens Cope 1878; Thecodontosaurus skirtopodus Seeley 1894; Thecodontosaurus polyzelus (Hitchcock 1865) von Huene 1906; Thecodontosaurus hermannianus von Huene 1908; Thecodontosaurus diagnosticus Fraas 1912; Thecodontosaurus minor Haughton 1918 (= "Thecodontosaurus minimus"); Thecodontosaurus dubius Haughton 1924; Thecodontosaurus browni (Seeley 1895) von Huene 1932 and Thecodontosaurus alophos Haughton 1932. All these are today referred to other genera or seen as nomina dubia. The last of these is Thecodontosaurus caducus named by Adam Yates
in 2003 for a juvenile specimen found in Wales
; in 2007 this was made the separate genus Pantydraco
.
Presently, the only valid species is thus T. antiquus.
Michael Benton
in 2000 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 tot 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
.
, the group containing lizards and snakes. This did not change when Richard Owen
in 1842 coined the Dinosauria, because Owen did not recognise Thecodontosaurus as a dinosaur; in 1865 he assigned it to the Thecodontia. Only in 1870 was Thomas Huxley
the first to understand it was a dinosaur, though referring it incorrectly to the Scelidosauridae. Later it would normally 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 but more recently it has been suggested that Thecodontosaurus and its relatives were prior to the prosauropod-sauropod split. New reconstructions show that its neck is proportionally shorter than in more advanced early sauropodomorphs.
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
of herbivorous
Herbivore
Herbivores are organisms that are anatomically and physiologically adapted to eat plant-based foods. Herbivory is a form of consumption in which an organism principally eats autotrophs such as plants, algae and photosynthesizing bacteria. More generally, organisms that feed on autotrophs in...
basal sauropodomorph dinosaur
Dinosaur
Dinosaurs are a diverse group of animals of the clade and superorder Dinosauria. They were the dominant terrestrial vertebrates for over 160 million years, from the late Triassic period until the end of the Cretaceous , when the Cretaceous–Paleogene extinction event led to the extinction of...
which lived during the late Triassic period
Triassic
The Triassic is a geologic period and system that extends from about 250 to 200 Mya . As the first period of the Mesozoic Era, the Triassic follows the Permian and is followed by the Jurassic. Both the start and end of the Triassic are marked by major extinction events...
(Norian
Norian
The Norian is a division of the Triassic geological period. It has the rank of an age or stage . The Norian lasted from 216.5 ± 2.0 to 203.6 ± 1.5 million years ago. It was preceded by the Carnian and succeeded by the Rhaetian.-Stratigraphic definitions:The Norian was named after the Noric Alps in...
and/or Rhaetian
Rhaetian
The Rhaetian is in geochronology the latest age of the Triassic period or in chronostratigraphy the uppermost stage of the Triassic system. It lasted from 203.6 ± 1.5 to 199.6 ± 0.6 million years ago...
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 that were discovered and one of the oldest that existed. Many species have been named in the genus but only the type species
Type species
In biological nomenclature, a type species is both a concept and a practical system which is used in the classification and nomenclature of animals and plants. The value of a "type species" lies in the fact that it makes clear what is meant by a particular genus name. A type species is the species...
Thecondontosaurus antiquus is seen as valid today.
Thecodontosaurus antiquus
In the autumn of 1834 surgeonSurgeon
In medicine, a surgeon is a specialist in surgery. Surgery is a broad category of invasive medical treatment that involves the cutting of a body, whether human or animal, for a specific reason such as the removal of diseased tissue or to repair a tear or breakage...
Henry Riley and curator
Curator
A curator is a manager or overseer. Traditionally, a curator or keeper of a cultural heritage institution is a content specialist responsible for an institution's collections and involved with the interpretation of heritage material...
of the Bristol Institution Samuel Stutchbury
Samuel Stutchbury
-External links:**...
began to excavate "saurian remains" at the quarry of Durdham Down
Durdham Down
Durdham Down is an area of public open space in Bristol, England. With its neighbour Clifton Down to the southwest, it constitutes a area known as The Downs, much used for leisure including walking, jogging and team sports. Its exposed position makes it particularly suitable for kite flying...
, at Clifton
Clifton, Bristol
Clifton is a suburb of the City of Bristol in England, and the name of both one of the city's thirty-five council wards. The Clifton ward also includes the areas of Cliftonwood and Hotwells...
, presently a part of Bristol
Bristol
Bristol is a city, unitary authority area and ceremonial county in South West England, with an estimated population of 433,100 for the unitary authority in 2009, and a surrounding Larger Urban Zone with an estimated 1,070,000 residents in 2007...
. 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 thekè, "socket", and 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
Megalosaurus
Megalosaurus is a genus of large meat-eating theropod dinosaurs of the Middle Jurassic period of Europe...
, Iguanodon
Iguanodon
Iguanodon is a genus of ornithopod dinosaur that lived roughly halfway between the first of the swift bipedal hypsilophodontids and the ornithopods' culmination in the duck-billed dinosaurs...
, Streptospondylus
Streptospondylus
Streptospondylus is a genus of tetanuran theropod dinosaur known from the Middle Jurassic period of France, 161 million years ago. It was a medium-sized predator.-Discovery and naming:...
and Hylaeosaurus
Hylaeosaurus
Hylaeosaurus is the most obscure of the three animals used by Sir Richard Owen to first define the new group Dinosauria, in 1842. The original specimen, recovered by Gideon Mantell from the Tilgate Forest in the south of England in 1832, now resides in the Natural History Museum of London, where...
, though Riley and Stutchbury were not aware of this, the very concept Dinosauria only being created in 1842. In 1843 John Morris
John Morris (geologist)
John Morris was an English geologist.Morris was professor of geology at University College, London from 1854 to 1877. He was awarded the Lyell Medal in 1876.-External links:*...
in his catalogue of British fossils provides a complete species name: Thecodontosaurus antiquus. The specific epithet, "antiquus", means "ancient" in Latin
Latin
Latin is an Italic language originally spoken in Latium and Ancient Rome. It, along with most European languages, is a descendant of the ancient Proto-Indo-European language. Although it is considered a dead language, a number of scholars and members of the Christian clergy speak it fluently, and...
.
The original type specimen or holotype
Holotype
A holotype is a single physical example of an organism, known to have been used when the species was formally described. It is either the single such physical example or one of several such, but explicitly designated as the holotype...
of Thecodontosaurus, BCM 1, a lower jaw, fell victim to heavy World War II
World War II
World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...
bombings by the Germans. Many remains of this dinosaur and other material related to it were destroyed in November 1940 during the Bristol Blitz
Bristol Blitz
Bristol was the fifth most heavily bombed British city of World War II. The presence of Bristol Harbour and the Bristol Aeroplane Company made it a target for bombing by the Nazi German Luftwaffe who were able to trace a course up the River Avon from Avonmouth using reflected moonlight on the...
. However, most bones were salvaged: 184 are today part of the collection of the Bristol City Museum and Art Gallery
Bristol City Museum and Art Gallery
The Bristol City Museum and Art Gallery is a large museum and art gallery in Bristol, England. It is run by the city council with no entrance fee. It holds designated museum status, granted by the national government to protect outstanding museums...
. Also, later some more remains were found near Bristol
Bristol
Bristol is a city, unitary authority area and ceremonial county in South West England, with an estimated population of 433,100 for the unitary authority in 2009, and a surrounding Larger Urban Zone with an estimated 1,070,000 residents in 2007...
at Tytherington
Tytherington, Gloucestershire
Tytherington is a village in South Gloucestershire, England. The quarry to the west belongs to Hanson plc.The former Yate to Thornbury railway branch line passes nearby, with two bridges in the village and a tank engine near the quarry entrance as reminders of the railway...
. At present in total about 245 fragmentary specimens are known, representing numerous individuals. In 1985 Peter Galton
Peter Galton
Peter M. Galton is a British vertebrate paleontologist working in America, who has to date written or co-written about a hundred papers in scientific journals or chapters in paleontology textbooks, especially on ornithischian and prosauropod dinosaurs.With Robert Bakker in a joint article...
designated another lower jaw, a right dentary, as the neotype, BCM 2. The remains have been found in chalkstone infillings, breccia
Breccia
Breccia is a rock composed of broken fragments of minerals or rock cemented together by a fine-grained matrix, that can be either similar to or different from the composition of the fragments....
deposited in fissures in older rocks. The age of these deposits was once estimated as old as the late Carnian
Carnian
The Carnian is the lowermost stage of the Upper Triassic series . It lasted from about 228.7 till 216.5 million years ago . The Carnian is preceded by the Ladinian and is followed by the Norian...
but recent studies indicate that they date from the Rhaetian
Rhaetian
The Rhaetian is in geochronology the latest age of the Triassic period or in chronostratigraphy the uppermost stage of the Triassic system. It lasted from 203.6 ± 1.5 to 199.6 ± 0.6 million years ago...
.
Other species
Apart from the original type speciesType species
In biological nomenclature, a type species is both a concept and a practical system which is used in the classification and nomenclature of animals and plants. The value of a "type species" lies in the fact that it makes clear what is meant by a particular genus name. A type species is the species...
, Thecodontosaurus antiquus, seventeen other species would be named in the genus.
Riley and Stutchbury also found some teeth of carnivorous phytosaurians that they named Paleosaurus cylindrodon and P. platyodon. In the late nineteenth century the theory became popular that such remains would have belonged to carnivorous prosauropods: animals with the body of Thecodontosaurus but with heads armed with slicing teeth. In 1890 Arthur Smith Woodward
Arthur Smith Woodward
Sir Arthur Smith Woodward was an English palaeontologist.-Biography:Woodward was born in Macclesfield, Cheshire, England and was educated there and at Owens College, Manchester. He joined the staff of the Department of Geology at the Natural History Museum in 1882. He became assistant Keeper of...
accordingly named a Thecodontosaurus platyodon, in 1908 Friedrich von Huene
Friedrich von Huene
Friedrich von Huene was a German paleontologist who named more dinosaurs in the early 20th century than anyone else in Europe.-Biography:...
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
Agrosaurus
Agrosaurus 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...
macgillivrayi, assuming the remains had been collected in 1844 by the crew of HMS Fly
HMS Fly (1831)
HMS Fly was an 18-gun sloop of the Royal Navy. She was responsible for the exploration and charting of much of Australia's north-east coast and nearby islands. She was converted to a coal hulk in 1855 and broken up in 1903.-Design and construction:...
on the northeast coast of Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
. It was long considered the first dinosaur found in Australia, but in 1999 it transpired that the bones probably belonged to a lot sent by Riley and Stutchbury to the British Museum of Natural History and then mislabelled. Already in 1906 von Huene had noted the close resemblance and renamed the species Thecodontosaurus macgillivrayi. It is thus a junior synonym of Thecodontosaurus antiquus.
It also happened that remains of completely different animal groups were referred to Thecodontosaurus. Thecodontosaurus latespinatus and Thecodontosaurus primus, both named by von Huene in 1905, were based on material from Tanystropheus
Tanystropheus
Tanystropheus , was a 6 metre long reptile that dated from the Middle Triassic period. It is recognisable by its extremely elongated neck, which measured 3 metres long - longer than its body and tail combined. Despite this length, it had only ten neck vertebrae, each quite long...
. In 1908 von Huene tentatively renamed Plateosaurus
Plateosaurus
Plateosaurus is a genus of plateosaurid dinosaur that lived during the Late Triassic period, around 216 to 199 million years ago, in what is now Central and Northern Europe. Plateosaurus is a basal sauropodomorph dinosaur, a so-called "prosauropod"...
elizae Sauvage 1907 into Thecodontosaurus? elizae; it is a nomen dubium
Nomen dubium
In zoological nomenclature, a nomen dubium is a scientific name that is of unknown or doubtful application...
based on theropod remains. The proterosuchid Ankistrodon
Ankistrodon
Ankistrodon is an extinct genus of archosaur first thought to be a dinosaur. It was later determined to be a proterosuchid archosauriform. 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...
Huxley 1865 was renamed Thecodontosaurus indicus.
A larger category consists of related basal sauropodomorphs assigned to Thecodontosaurus. These include in chronological order: Thecodontosaurus gibbidens Cope 1878; Thecodontosaurus skirtopodus Seeley 1894; Thecodontosaurus polyzelus (Hitchcock 1865) von Huene 1906; Thecodontosaurus hermannianus von Huene 1908; Thecodontosaurus diagnosticus Fraas 1912; Thecodontosaurus minor Haughton 1918 (= "Thecodontosaurus minimus"); Thecodontosaurus dubius Haughton 1924; Thecodontosaurus browni (Seeley 1895) von Huene 1932 and Thecodontosaurus alophos Haughton 1932. All these are today referred to other genera or seen as nomina dubia. The last of these is Thecodontosaurus caducus named by Adam Yates
Adam Yates
Adam Paul Yates is an English footballer who plays for League Two side Port Vale as a full back. He is a former semi-pro international with England....
in 2003 for a juvenile specimen found in Wales
Wales
Wales is a country that is part of the United Kingdom and the island of Great Britain, bordered by England to its east and the Atlantic Ocean and Irish Sea to its west. It has a population of three million, and a total area of 20,779 km²...
; in 2007 this was made the separate genus Pantydraco
Pantydraco
Pantydraco was a genus of basal sauropodomorph dinosaur from the Late Triassic of United Kingdom...
.
Presently, the only valid species is thus T. antiquus.
Description
From the fragmentary remains of Thecodontosaurus most of the skeleton can be reconstructed, the main exception being 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 (11.8 in) tall, and weighed 11 kilograms (24.3 lb). The largest individuals had an estimated length of 2.5 metres (8.2 ft).Michael Benton
Michael Benton
Michael J. Benton is a British paleontologist, a Fellow of the Royal Society of Edinburgh, and professor of vertebrate palaeontology in the Department of Earth Sciences at the University of Bristol....
in 2000 noted the existence of a robust morph
Morph
- Astronomy :* Morphs collaboration, a collaboration that studied the evolution of spiral galaxies using the Magellan and the Hubble Space Telescope- Biology :...
in the population, seen by him as a possible second species or, more likely, an instance of sexual dimorphism
Sexual dimorphism
Sexual dimorphism is a phenotypic difference between males and females of the same species. Examples of such differences include differences in morphology, ornamentation, and behavior.-Examples:-Ornamentation / coloration:...
. 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 tot the total length of the lower jaw; an ilium
Ilium
-Places:* Ilion or, Latinized, Ilium, another name for the legendary city of Troy, hence the title of Homer's Iliad*Ilium , an ancient city in Epirus...
that has a back end that is subquadrate instead of rounded.
The small size has been explained as an instance of insular dwarfism
Insular dwarfism
Insular dwarfism, a form of phyletic dwarfism, is the process and condition of the reduction in size of large animals – typically mammals – when their population's range is limited to a small environment, primarily islands. This natural process is distinct from the intentional creation of dwarf...
.
Phylogeny
Riley and Stutchbury originally saw Thecondontosaurus as a member of the SquamataSquamata
Squamata, or the scaled reptiles, is the largest recent order of reptiles, including lizards and snakes. Members of the order are distinguished by their skins, which bear horny scales or shields. They also possess movable quadrate bones, making it possible to move the upper jaw relative to the...
, the group containing lizards and snakes. This did not change when Richard Owen
Richard Owen
Sir Richard Owen, FRS KCB was an English biologist, comparative anatomist and palaeontologist.Owen is probably best remembered today for coining the word Dinosauria and for his outspoken opposition to Charles Darwin's theory of evolution by natural selection...
in 1842 coined the Dinosauria, because Owen did not recognise Thecodontosaurus as a dinosaur; in 1865 he assigned it to the Thecodontia. Only in 1870 was Thomas Huxley
Thomas Huxley
Thomas Henry Huxley PC FRS was an English biologist, known as "Darwin's Bulldog" for his advocacy of Charles Darwin's theory of evolution....
the first to understand it was a dinosaur, though referring it incorrectly to the Scelidosauridae. Later it would normally be placed in either the Anchisauridae
Anchisauridae
The Anchisauridae were a group of early sauropodomorph dinosaurs first proposed by Othniel Charles Marsh in 1885. The clade consists of Anchisaurus and its nearest relatives. However, it is not clear which other genera are included in the family; many of the dinosaurs once included have since been...
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
Sauropodomorpha
Sauropodomorpha is an extinct clade of long-necked, herbivorous, saurischian dinosaurs which 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...
dinosaurs. It was earlier included under the Prosauropoda but more recently it has been suggested that Thecodontosaurus and its relatives were prior to the prosauropod-sauropod split. New reconstructions show that its neck is proportionally shorter than in more advanced early sauropodomorphs.