On 23 May 1874, James Shopland of the Swindon Brick and Tyle Company reported in a letter to Professor
Richard Owen that their clay pit, the Swindon Great Quarry below Old Swindon Hill at
Swindon in
Wiltshire, had again produced a fossil skeleton that he was willing to donate to the
British Museum of Natural History. Owen sent out
William Davies to secure the specimen, which proved to be encased in an eight feet high and six feet wide clay
nodule. Owen presumed that the extremely hard nodule had been formed by vapours emitted by the decomposing carcass. During an attempt to lift it in its entirety, the loam clump crumbled into several pieces. These were eventually transported to London in crates with a total weight of three tonnes. The bones were subsequently partially uncovered by Owen's preparator, the mason Caleb Barlow. Owen named and described the remains in 1875 as the
type species Omosaurus armatus. The generic name is derived from Greek ὦμος,
omos, "upper arm", in reference to the robust
humerus. The
specific name armatus can mean "armed" in
Latin and in this case refers to a large spike that Owen assumed was present on the upper arm. The study was illustrated by high quality
lithographs. The
holotype,
NHMUK OR 46013, was found in a layer of the
Kimmeridge Clay Formation dating from the late
Kimmeridgian. The pits were soon abandoned; as a result it is no longer possible to determine their exact location and age. The holotype consists of a postcranial skeleton lacking the skull. The main nodule fragment contains the pelvis; a series of six posterior dorsal vertebrae, all sacrals and eight anterior caudal vertebrae; a right femur and some loose vertebrae. In all, thirteen detached vertebrae are present in the material. Also an almost complete left forelimb was contained by another loam clump. Additional elements include a partial right fibula with calcaneum, a partial tibia, a right neck plate and a left tail spike. Several other species would be named within the genus
Omosaurus. Part of the British Museum of Natural History collection was specimen NHMUK 46320, a pair of spike bases found in the Kimmeridge Clay by
William Cunnington near the
Great Western Railway cutting near
Wootton Bassett. These Owen in 1877 named
Omosaurus hastiger, the epithet meaning "spike-bearer" or "lance-wielder", the spikes by him seen as placed on the wrist of the animal. In 1887,
John Whitaker Hulke named
Omosaurus durobrivensis based on specimen NHMUK R1989 found at
Tanholt, close to
Eye, Cambridgeshire, the specific name being derived from
Durobrivae. (That specimen is sometimes mistakenly said to have been found at
Fletton, Peterborough, Cambridgeshire, which is where
Alfred Nicholson Leeds made most of his finds.) This in 1956 became the separate genus
Lexovisaurus. In 1893,
Harry Govier Seeley named
Omosaurus phillipsii, based on a left femur of a young individual found at
Slingsby, North Yorkshire, specimen YM 498, the epithet honouring the late
John Phillips. Seeley suggested this may be the same taxon as
Priodontognathus phillipsii Seeley 1869, which has led to the misunderstanding, due to its having the same specific name, that
Priodontognathus was simply subsumed by him under
Omosaurus. This interpretation however, is incorrect as both species have different holotypes.
O. phillipsii has been considered a
nomen dubium. "Omosaurus leedsi" is a
nomen nudum used by Seeley on a label for
CAMSM J.46874, a plate found in
Cambridgeshire, the epithet honouring
Alfred Nicholson Leeds. In 1910,
Friedrich von Huene named
Omosaurus vetustus, based on specimen OUM J.14000, a femur found in the west bank of
Cherwell River, the epithet meaning "the ancient one". In 1911,
Franz Nopcsa named
Omosaurus lennieri, the epithet honouring
Gustave Lennier, based on a partial skeleton in 1899 found in the Kimmeridgian
Argiles d'Octeville near in
Normandy, France. The specimen would be destroyed during an allied bombing of
Le Havre in 1944. The species was by
Peter Galton considered a junior synonym of
Omosaurus armatus in 1991. Even as the last two
Omosaurus species were named, it had become known that the name
Omosaurus had been
preoccupied by a "crocodilian" (in fact a
phytosaur),
Omosaurus perplexus Leidy 1856. This had been pointed out by
Othniel Charles Marsh during a visit to Great Britain. In 1900,
Richard Lydekker tried to solve this by subsuming the first species under
Stegosaurus, as a
Stegosaurus armatus and a
Stegosaurus hastiger. It had escaped him that Marsh had already named a
Stegosaurus armatus in 1877. In 1902,
Frederick Augustus Lucas renamed the genus into
Dacentrurus. The name is derived from Greek δα~,
da~, "very" or "full of", κέντρον,
kentron, "point", and οὐρά,
oura, "tail". Lucas only gave a
new combination name for the type species
Omosaurus armatus:
Dacentrurus armatus, but in 1915
Edwin Hennig moved most
Omosaurus species to
Dacentrurus, resulting in a
Dacentrurus hastiger,
Dacentrurus durobrivensis,
Dacentrurus phillipsi and a
Dacentrurus lennieri. Nevertheless, it would be common for researchers to use the name
Omosaurus instead until the middle of the twentieth century.
D. vetustus, earlier indicated as
Omosaurus (
Dacentrurus)
vetustus by von Huene, was
included with
Lexovisaurus as a
Lexovisaurus vetustus in 1983, but that assignment was rejected with both editions of the
Dinosauria, and
O. vetustus is now the type species of "
Eoplophysis". In 2021, remains attributed to
Dacentrurus sensu lato were reported from the earliest Cretaceous (
Berriasian)
Angeac-Charente bonebed of France. These consisted of a partial skeleton including parts of the braincase, vertebrae, ribs and phalanges. In 2024, 11 specimens (including the holotype and referred material of
Miragaia longicollum) from France, Portugal, and Spain were assigned to
Dacentrurus armatus.
Distribution Due to the fact it represented the best known stegosaurian species from Europe, the first known from articulated remains, most stegosaur discoveries in this area were referred to
Dacentrurus. This included finds in
Wiltshire and
Dorset in southern England (among them a vertebra ascribed to
D. armatus in
Weymouth), fossils from France and Spain and five more historically recent skeletons from Portugal. Most of these finds were fragmentary in nature; the only more complete skeletons were the holotypes of
D. armatus and
D. lennieri. Eventually the strata from which
Dacentrurus was reported amounted to the following list: •
Argiles d'Octeville •
Camadas de Alcobaça •
Unidade Bombarral were in 1981 by Galton identified as a
Dacentrurus juvenile.
Peter Malcolm Galton in the eighties referred all stegosaur remains from Late Jurassic deposits in western Europe to
D. armatus. In 2013, Alberto Cobos and Francisco Gascó described stegosaurian vertebral remains, which were found grouped together in the "Barranco Conejero" locality of the
Villar del Arzobispo Formation in Riodeva (
Teruel, Spain). The remains were assigned to
Dacentrurus armatus and consist of four vertebral centra, specimens MAP-4488-4491, from a single individual, two of which are
cervical vertebrae; the third is a
dorsal, and the last is a
caudal. This discovery was considered significant because it would demonstrate both the intra-specific variability of
Dacentrurus armatus, and the strong prevalence of
Dacentrurus in the Iberian range during the
Jurassic-
Cretaceous boundary, approximately 145 million years ago. However, Sánchez-Fenollosa et al. (2024) supported the synonymy of the two taxa based on the new specimen of
Dacentrurus from the
Villar del Arzobispo Formation, and suggested that
Alcovasaurus is a separate genus. == Description ==