Dacentrurus (meaning “tail full of points”), originally known as Omosaurus, was a large stegosaur of the Late Jurassic Period (154 – 150 mya) of Europe. Its type species, Omosaurus armatus, was named in 1875, based on a skeleton found in England. In 1902 the genus was renamed into Dacentrurus because the name Omosaurus had already been used for a crocodilian. 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.
Dacentrurus was a large stegosaurid. Some specimens have been estimated to reach lengths between 7–8 m (23–26 ft) and to weigh up to 5 t (5.5 short tons). Many books claim that Dacentrurus was a small stegosaur, when in fact finds such as a 1.5 metres (4.9 ft) wide pelvis indicate that Dacentrurus was among the largest of them. For a stegosaur the gut was especially broad, and a massive rump is also indicated by exceptionally wide dorsal vertebrae centra. The hindlimb was rather short, but the forelimb relatively long, largely because of a long lower arm.
Although Dacentrurus is considered to have the same proportions as Stegosaurus, its plate and spike configuration is known to be rather different, as it probably had both two rows of small plates on its neck and two rows of longer spikes along its tail. The holotype specimen of Dacentrurus armatus contained a small blunt asymmetrical neck plate and also included a tail spike which could have been part of a thagomizer. The tail spike had sharp cutting edges on its front and rear side.
Dacentrurus has sometimes been portrayed with a spike growing near the shoulder, similarly to a Kentrosaurus. Whether this portrayal is accurate or not is not yet determined.
Due to the fact it represented the best known stegosaurian species from Europe, 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. .
Study of late Jurassic ecosystems in North America has brought the strong suggestion that stegosaurs regularly came into conflict with theropod dinosaurs like Allosaurus. This predator/prey interaction may have also happened in late Jurassic Europe, although most of the large theropods such as Dubreuillosaurus and Poekilopleuron are so far only known from earlier in the Jurassic.