Centrosaurus

''Centrosaurus'' ( ; ) is a genus of centrosaurine ceratopsian dinosaur from Campanian age of Late Cretaceous Canada. Their remains have been found in the Dinosaur Park Formation, dating from 76.5 to 75.5 million years ago.

Discovery and naming

The first ''Centrosaurus'' remains were discovered and named by paleontologist Lawrence Lambe in strata along the Red Deer River in Alberta. The name ''Centrosaurus'' means "pointed lizard" (from Greek ', , "point" and ', , "lizard") and refers to, the series of small hornlets placed along the margin of their frills, not the nasal horns (which were unknown when the dinosaur was named). The genus is not to be confused with the stegosaur ''Kentrosaurus'', the name of which is derived from the same Greek word.

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. The area is now known as the Hilda mega-bonebed.

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 believed one species of ''Monoclonius'', ''M. nasicornus'', may actually have been a female ''Styracosaurus''.Dodson, P. (1996). ''The Horned Dinosaurs: A Natural History''. Princeton University Press: Princeton, New Jersey, pp. 197–199. . His assessments have been partially followed, with other researchers not accepting ''Monoclonius nasicornus'' as a female ''Styracosaurus'' or ''Monoclonius'' as a valid genus. While sexual dimorphism has been proposed for a more basal ceratopsian, ''Protoceratops'', there is no firm evidence for sexual dimorphism in any ceratopsid.Forster, C. A. (1990). The cranial morphology and systematics of ''Triceratops'', with a preliminary analysis of ceratopsian phylogeny. Ph.D. Dissertation. University of Pennsylvania, Philadelphia. 227 pp. Others have synonymized ''C. nasicornus'' with ''C. apertus'', or considered it a separate ''Centrosaurus'' species: ''Centrosaurus nasicornus''. It has also been suggested as the direct ancestor of ''Styracosaurus albertensis''. A 2014 study of changes during growth in ''Centrosaurus'' concluded that ''C. nasicornus'' is a junior synonym of ''C. apertus'', representing a middle growth stage.

The species ''C. brinkmani'', described in 2005, was moved to the new genus '' Coronosaurus'' in 2012.

Description

''Centrosaurus'' were large dinosaurs, although not as large as some of their relatives, reaching long and in body mass situated atop stocky limbs. Like other centrosaurines, ''Centrosaurus'' bore a single large horn over their noses. These horns curved forwards or backwards depending on the specimen. Skull ornamentation was reduced as animals aged. The frill was relatively short compared to the total skull length and could grow to over half a meter (68.8 cm) long in the oldest and largest adults.

''Centrosaurus'' is distinguished by having two large hornlets which hook forwards over the frill. A pair of small upwards directed horns is also found over the eyes. The frills of ''Centrosaurus'' were moderately long, with fairly large fenestrae and small hornlets along the outer edges.

Classification

The genus ''Centrosaurus'' gives its name to the Centrosaurinae subfamily. 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 subfamily include '' Pachyrhinosaurus'', ''Avaceratops'', '' Einiosaurus'', '' Albertaceratops'', and ''Achelousaurus''.

The cladogram presented below represents a phylogenetic analysis by Chiba ''et al.'' (2017):

Paleobiology

Like other ceratopsids, the jaws of ''Centrosaurus'' were adapted to shear through tough plant material. The discovery of gigantic bone beds of ''Centrosaurus'' in Canada suggest that they were gregarious animals and could have traveled in large herds."Centrosaurus." In: Dodson, Peter & Britt, Brooks & Carpenter, Kenneth & Forster, Catherine A. & Gillette, David D. & Norell, Mark A. & Olshevsky, George & Parrish, J. Michael & Weishampel, David B. ''The Age of Dinosaurs''. Publications International, LTD. p. 135. . 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 skulls were more likely caused by intraspecific combat (horn-to-horn combat) rather than predatory attacks. The frills of ''Centrosaurus'' were too thin to be used for defense against predators, although the thicker, solid frills of ''Triceratops'' might have evolved to protect their necks. The frills of ''Centrosaurus'' were most likely used "for species recognition and/or other forms of visual display".

Paleopathology

A specimen of ''Centrosaurus apertus'' recovered from Dinosaur Provincial Park in 1989 was discovered to have crippling osteosarcoma in its right fibula. Examination of the cancerous lesions in the bone suggest the cancer had reached an aggressive stage. The cancer would have resulted in a severe limp that would have made the ceratopsian more vulnerable to predation. However, the fact that it was part of a herd allowed the ''Centrosaurus'' to survive much longer than would be expected for an animal infected with such severe disease. The individual itself is believed to have died from drowning in the flash flood that created the ''Centrosaurus'' bone bed where it was found. The specimen remains one of the few dinosaur specimens found with severe cancer.

Paleobiogeography

Thomas M. Lehman has observed that ''Centrosaurus'' fossils haven't been found outside of southern Alberta even though they are among the most abundant Judithian dinosaurs in the region. Large herbivores like the ceratopsians living in North America during the Late Cretaceous had "remarkably small geographic ranges" despite their large body size and high mobility. This restricted distribution strongly contrasts with modern mammalian faunas whose large herbivores' ranges "typical y... span much of a continent."Lehman, T. M., 2001, Late Cretaceous dinosaur provinciality: In: Mesozoic Vertebrate Life, edited by Tanke, D. H., and Carpenter, K., Indiana University Press, pp. 310-328. Fossil material of ''C. apertus'' was subsequently described from the strata of the Dinosaur Park Formation in Saskatchewan.

See also

* Timeline of ceratopsian research

References

*

External links

''Centrosaurus''
at The Dinosaur Picture Database

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Centrosaurinae
Dinosaur genera
Campanian dinosaurs
Dinosaur Park Formation
Fossil taxa described in 1904
Taxa named by Lawrence Lambe
Dinosaurs of Canada