Dacentrurus

''Dacentrurus'' (meaning "tail full of points"), originally known as ''Omosaurus'', is a genus of stegosaurian dinosaur from the Late Jurassic to 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 crocodylian. 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 a heavily built quadrupedal herbivore, adorned with plates and spikes, reaching in length and in body mass.

Discovery and species

On 23 May 1874, James Shopland of the Swindon Brick and Tyle Company reported 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. Owen sent out William Davies to secure the specimen, which proved to be encased in an eight feet high clay nodule. 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 holotype, BMNH 46013, was found in a layer of the Kimmeridge Clay Formation dating from the late Kimmeridgian. 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 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 BMNH 46321, 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 BMNH 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 femur, 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. "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 the allied bombing of Caen

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