Dacentrurus (meaning "tail full of points") is an extinct genus of stegosaurian dinosaur from the Late Jurassic and perhaps Early Cretaceous (154–140 million years ago) of Europe. Its type species, D. armatus, was named in 1875 as Omosaurus armatus, based on a skeleton found in a clay pit in the Kimmeridge Clay in Swindon, England. In 1902 the genus was renamed Dacentrurus because the name Omosaurus had already been used for a phytosaur in 1856. After 1875, half a dozen other species would be named but perhaps only Dacentrurus armatus is valid.
Dacentrurus is among the largest known stegosaurs, measuring around long and weighing up to . Finds of this animal have been limited, so much of its appearance is uncertain and its relationship with other members of the Dacentrurinae are contentious. Some researchers suggest that Miragaia longicollum represents a junior synonym of this taxon.
Discovery and species
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.Davis, W., 1876, "On the exhumation and development of a large reptile (Omosaurus armatus, Owen), from the Kimmeridge Clay, Swindon, Wilts.", Geological Magazine, 3: 193–197
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.R. Owen, 1875, Monographs on the fossil Reptilia of the Mesozoic formations. Part II. (Genera Bothriospondylus, Cetiosaurus, Omosaurus). The Palaeontographical Society, London 1875: 15-93
The holotype, NHMUK PV 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 PV OR 46013, 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.R. Owen, 1877, Monographs on the fossil Reptilia of the Mesozoic formations. Part III. (Omosaurus). The Palaeontographical Society, London 1877 :95-97
In 1887, John Whitaker Hulke named Omosaurus durobrivensis based on specimen NHMUK PV R 1989 found at Tanholt, close to Eye, Cambridgeshire, the specific name being derived from Durobrivae.J. W. Hulke, 1887, "Note on some dinosaurian remains in the collection of A. Leeds, Esq, of Eyebury, Northamptonshire", Quarterly Journal of the Geological Society 43: 695-702 (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, H. G., 1893, "Omosaurus phillipsi", Yorkshire Philosophical Society, Annual Report 1892, p. 52-57 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.Galton, P.M. 1983. "A juvenile stegosaurian dinosaur, Omosaurus phillipsi SEELEY from the Oxfordian (Upper Jurassic) of England". Géobios 16: 95-101 "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.Seeley, H. G., 1901, (in Huene, F.): Centralblatt für Minerologie, Geologie und Paläontologie 1901, p. 718
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".Huene, F. von, 1910, "Über den altesten Rest von Omosaurus (Dacenturus) im englischen Dogger", Neues Jahrbuch für Mineralogie, Geologie und Paläontologie, 1910(1): 75-78 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.Nopcsa, F., 1911, "Omosaurus lennieri, un nouveau Dinosaurien du Cap de la Hève", Bulletin de la Société Geologique de Normandie 30: 23-42 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.J. Leidy, 1856, "Notice of remains of extinct vertebrated animals discovered by Professor E. Emmons", Proceedings of the Academy of Natural Sciences of Philadelphia 8: 255-257 This had been pointed out by Othniel Charles Marsh during a visit to Great Britain.Lydekker, Richard, 1888, "British Museum catalogue of fossil reptiles, and papers on the enaliosaurians'. Geological Magazine (3)5: 451-453 In 1900, Richard Lydekker tried to solve this by subsuming the first species under Stegosaurus, as a Stegosaurus armatus and a Stegosaurus hastiger.Richard Lydekker, 1890, Catalogue of the fossil Reptilia and Amphibia in the British Museum. Part IV. - 295 pp., 66 Figs.; London (British Museum of Natural History) 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".F.A. Lucas, 1902, "Paleontological notes. The generic name Omosaurus: A new generic name for Stegosaurus marshi", Science, new series 16(402): 435 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.Hennig, E., 1915, Stegosauria: Fossilium Catalogus I, Animalia pars 9, p. 1-16 Nevertheless, it would be common for researchers to use the name Omosaurus instead until the middle of the twentieth century.Maidment, S. C. R., 2010, "Stegosauria: a historical review of the body fossil record and phylogenetic relationships", Swiss Journal of Geosciences 103(2): 199-210 D. vetustus, earlier indicated as Omosaurus (Dacentrurus) vetustus by von Huene, was included with Lexovisaurus as a Lexovisaurus vetustus in 1983,Galton, P. M. and Powell, H. P., 1983, "Stegosaurian dinosaurs from the Bathonian (Middle Jurassic) of England, the earliest record of the family Stegosauridae", Geobios, 16: 219–229 but that assignment was rejected with both editions of the Dinosauria,P. M. Galton. 1990. Stegosauria. The Dinosauria, D. B. Weishampel, P. Dodson, and H. Osmólska (editors), University of California Press, Berkeley 435-455 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.Ronan Allain, Romain Vullo, Lee Rozada, Jérémy Anquetin, Renaud Bourgeais, et al. Vertebrate paleobiodiversity of the Early Cretaceous (Berriasian) Angeac-Charente Lagerstätte (southwestern France): implications for continental faunal turnover at the J/K boundary. Geodiversitas, Museum National d'Histoire Naturelle Paris, In press. ffhal-03264773f
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.Alberto Cobos and Francisco Gascó. (2013) New vertebral remains of the stegosaurian dinosaur Dacentrurus from Riodeva (Teruel, Spain). Geogaceta, 53, 17-20. This included finds in Wiltshire and Dorset in southern England (among them a vertebra ascribed to D. armatus in WeymouthGalton P.M. (1985) "British plated dinosaurs (Ornithischia, Stegosauridae), Journal of Vertebrate Paleontology, 5: 211-254), 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'OctevilleGalton, Peter M.; Upchurch, Paul (2004). "Stegosauria (Table 16.1)." In: Weishampel, David B.; Dodson, Peter; and Osmólska, Halszka (eds.): The Dinosauria, 2nd, Berkeley: University of California Press. Pp. 344-345. . Camadas de Alcobaça Kimmeridge Clay Lourinhã Formation Unidade Bombarral Villar del Arzobispo Formation
A longitudinally sectioned egg, with a length of 125 millimetres, from Portugal has been attributed to Dacentrurus, the first associated with any stegosaur.
Remains in 1957 named as a sauropod, Astrodon pusillus,Lapparent, Albert F. de & Zbyszewski, Georges, 1957, "Les dinosauriens du Portugal". Memoires de Service géologique de Portugal (N.S.) 2: 1-63 were in 1981 by Galton identified as a Dacentrurus juvenile.Galton, P.M. 1981. "A juvenile stegosaurian dinosaur, >>Astrodon pusillus<<, from the Upper Jurassic of Portugal, with comments on Upper Jurassic and Lower Cretaceous biogeography". Journal of Vertebrate Paleontology 1(3/4):245-256