''Thecospondylus'' (THEEK-o-SPON-di-lus, "sheath vertebra") is a

dubious Doubt is a mental state in which the mind remains suspended between two or more contradictory propositions, unable to be certain of any of them. Doubt on an emotional level is indecision between belief and disbelief. It may involve uncertainty ...

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...

dinosaur Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the evolution of dinosaurs is t ...

from the

Early Cretaceous The Early Cretaceous ( geochronological name) or the Lower Cretaceous (chronostratigraphic name), is the earlier or lower of the two major divisions of the Cretaceous. It is usually considered to stretch from 145 Ma to 100.5 Ma. Geology Pro ...

England England is a country that is part of the United Kingdom. It shares land borders with Wales to its west and Scotland to its north. The Irish Sea lies northwest and the Celtic Sea to the southwest. It is separated from continental Europe b ...

. Scientists are unsure as to whether ''Thecospondylus'' was a

saurischian Saurischia ( , meaning "reptile-hipped" from the Greek ' () meaning 'lizard' and ' () meaning 'hip joint') is one of the two basic divisions of dinosaurs (the other being Ornithischia), classified by their hip structure. Saurischia and Ornithis ...

or an

ornithischian Ornithischia () is an extinct order of mainly herbivorous dinosaurs characterized by a pelvic structure superficially similar to that of birds. The name ''Ornithischia'', or "bird-hipped", reflects this similarity and is derived from the Greek st ...

History

Dr. A.C. Horner, an amateur geologist living at

Tonbridge Tonbridge ( ) is a market town in Kent, England, on the River Medway, north of Royal Tunbridge Wells, south west of Maidstone and south east of London. In the administrative borough of Tonbridge and Malling, it had an estimated populat ...

, in the nineteenth century acquired a fossil found in the quarry of Southborough. He sent it to

paleontologist Paleontology (), also spelled palaeontology or palæontology, is the scientific study of life that existed prior to, and sometimes including, the start of the Holocene epoch (roughly 11,700 years before present). It includes the study of fossi ...

Harry Govier Seeley Harry Govier Seeley (18 February 1839 – 8 January 1909) was a British paleontologist. Early life Seeley was born in London on 18 February 1839, the second son of Richard Hovill Seeley, a goldsmith, and his second wife Mary Govier. When his fat ...

who in 1882 described and named it as the

type species In zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the species that contains the biological type specimen ...

''Thecospondylus horneri''. The genus name is derived from

Greek Greek may refer to: Greece Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group. *Greek language, a branch of the Indo-European language family. **Proto-Greek language, the assumed last common ancestor ...

''theke'' meaning 'sheath' and ''spondylos'' meaning '

vertebra The spinal column, a defining synapomorphy shared by nearly all vertebrates, Hagfish are believed to have secondarily lost their spinal column is a moderately flexible series of vertebrae (singular vertebra), each constituting a characteristi ...

', a reference to the "extremely thin" bone forming the vertebrae. The specific name honours Horner. The

holotype A holotype is a single physical example (or illustration) of an organism, known to have been used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of several ...

, BMNH R.291, was found in a layer of the Hastings Sand,

sandstone Sandstone is a clastic sedimentary rock composed mainly of sand-sized (0.0625 to 2 mm) silicate grains. Sandstones comprise about 20–25% of all sedimentary rocks. Most sandstone is composed of quartz or feldspar (both silicates) ...

dating from the

Valanginian In the geologic timescale, the Valanginian is an age or stage of the Early or Lower Cretaceous. It spans between 139.8 ± 3.0 Ma and 132.9 ± 2.0 Ma (million years ago). The Valanginian Stage succeeds the Berriasian Stage of the Lower Cretace ...

Hauterivian The Hauterivian is, in the geologic timescale, an age in the Early Cretaceous Epoch or a stage in the Lower Cretaceous Series. It spans the time between 132.9 ± 2 Ma and 129.4 ± 1.5 Ma (million years ago). The Hauterivian is preceded by the ...

. It consist of an elongated natural internal cast or

endocast An endocast is the internal cast of a hollow object, often referring to the cranial vault in the study of brain development in humans and other organisms. Endocasts can be artificially made for examining the properties of a hollow, inaccessible sp ...

of the

neural canal In the developing chordate (including vertebrates), the neural tube is the embryonic precursor to the central nervous system, which is made up of the brain and spinal cord. The neural groove gradually deepens as the neural fold become elevated, ...

of the sacrum, about sixty centimetres long. It shows the divisions of at least five and probably seven sacral vertebrae. On three of them the

cancellous bone A bone is a rigid organ that constitutes part of the skeleton in most vertebrate animals. Bones protect the various other organs of the body, produce red and white blood cells, store minerals, provide structure and support for the body, and ...

is still present to which the generic name is referring. It is the only known fossil that can be definitely assigned to this genus. A second species, ''T. daviesi'', was added by Seeley in 1888, but later given its own genus, '' Thecocoelurus''. In 1926 Friedrich von Huene renamed ''T. horneri'' to ''Thecocoelurus horneri'',F. v. Huene, 1926, "The carnivorous Saurischia in the Jura and Cretaceous formations, principally in Europe", ''Revista del Museo de La Plata'' 29: 35-167 but this has not been commonly accepted, because ''Thecospondylus'' would have priority.

Classification

Based on such meagre material, the affinities of ''T. horneri'' have been hard to determine. Seeley himself merely assigned it to Dinosauria.

Richard Lydekker Richard Lydekker (; 25 July 1849 – 16 April 1915) was an English naturalist, geologist and writer of numerous books on natural history. Biography Richard Lydekker was born at Tavistock Square in London. His father was Gerard Wolfe Lydekker, ...

in 1888 referred it to the

Sauropoda Sauropoda (), whose members are known as sauropods (; from '' sauro-'' + '' -pod'', 'lizard-footed'), is a clade of saurischian ('lizard-hipped') dinosaurs. Sauropods had very long necks, long tails, small heads (relative to the rest of their bo ...

. Von Huene however in 1909 considered it to be a member of the

theropod Theropoda (; ), whose members are known as theropods, is a dinosaur clade that is characterized by hollow bones and three toes and claws on each limb. Theropods are generally classed as a group of saurischian dinosaurs. They were ancestrally c ...

family

Coeluridae Coeluridae is a historically unnatural group of generally small, carnivorous dinosaurs from the late Jurassic Period. For many years, any small Jurassic or Cretaceous theropod that did not belong to one of the more specialized families recognize ...

. Recent authors conclude it is a '' nomen dubium'', of which it is not even certain whether it is a

saurischia Saurischia ( , meaning "reptile-hipped" from the Greek ' () meaning 'lizard' and ' () meaning 'hip joint') is one of the two basic divisions of dinosaurs (the other being Ornithischia), classified by their hip structure. Saurischia and Ornithis ...

n or an ornithischian.

References

Dinosaur genera Hauterivian life Valanginian life Early Cretaceous dinosaurs of Europe Cretaceous England Fossils of England Fossil taxa described in 1882 Taxa named by Harry Seeley Nomina dubia {{dinosaur-stub