Қазбаға түскен тікенді құйрықты динозавр (Qazbağa tüsken tikenli qūyryqty dinozavr)

Extinct species of reptile

Dacentrurus (meaning "tail full of points"), originally known as Omosaurus, is a genus of stegosaurian dinosaur from the Late Jurassic and perhaps Early Cretaceous (154 140 mya) of Europe. Its type species, Omosaurus armatus, was named in 1875, 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. After 1875, half a dozen other species would be named but perhaps only Dacentrurus armatus is valid. Finds of this animal have been limited and much of its appearance is uncertain. It was the largest stegosaur measuring around long and weighing up to
The relationships between Dacentrurus and other Dacentrurinae, such as Miragaia, are contentious.

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.

Dacentrurus was one of the largest species of stegosaur along with Stegosaurus, with some specimens have been estimated to reach in length, in hip height and in body mass. For a stegosaur, the gut was especially broad, The hindlimb was rather short,

If the material is limited to the holotype, as Maidment proposed, only a single autapomorphy, unique derived trait, remains: the straight upper edge of the ischium. However, in 2019 three more possible autapomorphies were established, based on Spanish material. The front end of the prepubis is expanded to below. The tip of the neural spines of the neck vertebrae is expanded to behind. The transverse processes of the neck vertebrae are located at midheight of the prezygapophyses, the front articulation processes. The holotype specimen of Dacentrurus armatus contained a small blunt asymmetrical neck or front back plate. Its base length is fifteen centimetres and the transverse width is seven centimetres. The base is oblique and the longest plate surface seems to be on the outside. Seen from that side it is pointing obliquely to the rear. The outer surfaces are smooth but the ventral surface is porous with irregular depressions. In 1969, Ronald Steel agreed, even though Dacentrurus showed basal traits as an apparent lack of dermal plates and a long forelimb. In 1981, Galton considered the low angle of the transverse processes, close to that of most other ornithischians, as a plesiomorphy. The same would be true of the low columnar pedicel of the neural arches. Therefore, despite dermal plates in fact being present, he concluded that Dacentrurus was an early off shoot of the stegosaurian tree. In 2008 and 2010 studies determined it as forming the clade Dacentrurinae with its sister species Miragaia longicollum. The Dacentrurinae were the sister group of Stegosaurus (Stegosaurinae sensu Sereno). The following cladogram shows the position of Dacentrurus armatus within the Thyreophora according to Maidment (2010):

Dacentrurus shares with other Dacentrurinae the presence of large olecranon horns on the ulnae. Combined with large deltoid crests on the humerus, they suggest a powerful musculus deltoideus making a strong humeral flexion and abduction possible. The forelimbs could then be firmly anchored on the ground wile the tail was forcefully swept from side to side, allowing the thagomizer to defend against large theropod predators, such as Torvosaurus.