Centrosaurus (pronounced /ˌsɛtrɵˈsɔrəs/ SEN-tro-SAWR-əs) is a genus of herbivorous ceratopsian dinosaurs from the late Cretaceous of Canada. Its remains have been found in the Dinosaur Park Formation and uppermost Oldman Formation, dating from 76.5 to 75.5 million years ago.
The name Centrosaurus means "pointed lizard" (from Greek kentron/κεντρον = "point or prickle" + sauros/σαυρος = "lizard"), and refers to the series of small hornlets placed along the margin of the frill, not to the horn on its nose (which was unknown when the dinosaur was named). It is not to be confused with the stegosaur Kentrosaurus, whose name is derived from the same Greek word.
Restoration of two Centrosaurus'Centrosaurus massive body was borne by stocky limbs, although at 18–20 ft (6m) it was not a particularly large dinosaur. Like other centrosaurines, Centrosaurus had a single large horn over the nose.. It may curve forwards or backwards in different species.
A pair of small horns is also found over the eyes; in Centrosaurus apertus these are directed upwards, whereas they are directed to the sides in C. brinkmani. The frill of Centrosaurus was moderately long, with fairly large fenestrae and small hornlets along the outer edge.
C. apertus is distinguished by having two large hornlets which hook forwards over the frill, while in C. brinkmani these hornlets are small and covered with small, finger-like growths.
The first Centrosaurus remains were discovered by paleontologist Lawrence Lambe in strata along the Red Deer River in Alberta, Canada. Later, vast bonebeds of Centrosaurus were found in Dinosaur Provincial Park, also in Alberta. Some of these beds extend for hundreds of meters and contain thousands of individuals of all ages and all levels of completion. Scientists have speculated that the high density and number of individuals would be explained if they had perished while trying to cross a flooded river. A discovery of thousands of Centrosaurus fossils near the town of Hilda, Alberta, is believed to be the largest bed of dinosaur bones ever discovered.
Skin impression of Centrosaurus'Centrosaurus gives its name to the Centrosaurinae subfamily to which it belongs. These were large North American horned dinosaurs characterized by their "prominent nasal horns, subordinate brow horns, short squamosals in a short frill, a tall, deep face relative to the ceratopines, and a projection into the rear of the nasal fenestra." Its closest relatives appear to be Styracosaurus and Monoclonius. It so closely resembles the latter of these that some paleontologists have considered them to represent the same animal.
Other members of the Centrosaurinae clade include Pachyrhinosaurus, Avaceratops, Einiosaurus, Albertaceratops, Achelousaurus, and possibly Brachyceratops, although Brachyceratops is dubious. Because of the variation between species and even individual specimens of centrosaurines, there has been much debate over which genera and species are valid, particularly whether Centrosaurus and/or Monoclonius are valid genera, undiagnosable, or possibly members of the opposite sex. In 1996, Peter Dodson found enough variation between Centrosaurus, Styracosaurus, and Monoclonius to warrant separate genera, and that Styracosaurus resembled Centrosaurus more closely than either resembled Monoclonius. Dodson also believed one species of Monoclonius, M. nasicornis, may actually have been a female Styracosaurus. His assessments have been partially followed, with other researchers not accepting Monoclonius nasicornis as a female Styracosaurus, or Monoclonius as a valid genus. While sexual dimorphism has been proposed for an earlier ceratopsian, Protoceratops, there is no firm evidence for sexual dimorphism in any ceratopsid.
Centrosaurus apertus skull in the Royal Ontario Museum, Toronto.Like other Ceratopsidae, the jaws of Centrosaurus were designed to shear through tough plant material; the frill provided an attachment for large jaw muscles. The discovery of gigantic bone beds of Centrosaurus in Canada suggest that it was a gregarious animal and could have traveled in large herds. A bone bed composed of Centrosaurus and Styracosaurus remains is known from the Dinosaur Park Formation in what is now Alberta. The mass deaths may have been caused by otherwise non-herding animals gathering around a waterhole during a drought. Centrosaurus is found lower in the formation than Styracosaurus, indicating that Centrosaurus was displaced by Styracosaurus as the environment changed over time.
The large frills and nasal horns of the ceratopsians are among the most distinctive facial adornments of all dinosaurs. Their function has been the subject of debate since the first horned dinosaurs were discovered. Common theories concerning the function of ceratopsian frills and horns include defense from predators, combat within the species, and visual display. A 2009 study of Triceratops and Centrosaurus skull lesions found that bone injuries on the skull were more likely caused by intraspecific combat (horn-to-horn combat) rather than predatory attacks. The frill of Centrosaurus was too thin to be used for defense against predators, although the thicker, solid frill of Triceratops might have evolved to protect the neck. The frill of Centrosaurus was most likely used "for species recognition and/or other forms of visual display".