| Centrosaurus | |
|---|---|
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| Skull ROM 767 from Dinosaur Provincial Park | |
Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Clade: | Dinosauria |
| Clade: | †Ornithischia |
| Clade: | †Ceratopsia |
| Family: | †Ceratopsidae |
| Subfamily: | †Centrosaurinae |
| Clade: | †Eucentrosaura |
| Tribe: | †Centrosaurini |
| Genus: | †Centrosaurus Lambe 1904 |
| Species: | †C. apertus |
| Binomial name | |
| †Centrosaurus apertus Lambe 1904 | |
| Synonyms | |
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Centrosaurus (/ˌsɛntroʊˈsɔːrəs/SEN-troh-SOR-əs;lit. 'pointed lizard') is agenus ofcentrosaurineceratopsiddinosaur from theCampanianage of theLate Cretaceous ofCanada. Its remains have been found in theDinosaur Park Formation, dating from 76.5 to 75.5 million years ago.[1] The type and only species seen as valid today isCentrosaurus apertus.
The firstCentrosaurus remains were discovered and named by paleontologistLawrence Lambe in strata along theRed Deer River inAlberta. The nameCentrosaurus means "pointed lizard" (fromGreekkentron,κέντρον, "point" andsauros,σαῦρος, "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 thestegosaurKentrosaurus, the name of which is derived from the same Greek word.
Later, vast bonebeds ofCentrosaurus were found inDinosaur Provincial Park, also inAlberta. 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.[2] A discovery of thousands ofCentrosaurus fossils near the town ofHilda,Alberta, is believed to be the largest bed of dinosaur bones ever discovered. The area is now known as theHilda mega-bonebed.[3]
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 whetherCentrosaurus and/orMonoclonius are valid genera, undiagnosable, or possibly members of the opposite sex. In 1996,Peter Dodson found enough variation betweenCentrosaurus,Styracosaurus, andMonoclonius to warrant separate genera and thatStyracosaurus resembledCentrosaurus more closely than either resembledMonoclonius.
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Dodson believed one species ofMonoclonius,M. nasicornus, may actually have been a femaleStyracosaurus.[4] His assessments have been partially followed, with other researchers not acceptingMonoclonius nasicornus as a femaleStyracosaurus orMonoclonius as a valid genus.[5] Whilesexual dimorphism has been proposed for a more basal ceratopsian,Protoceratops,[6] there is no firm evidence for sexual dimorphism in any ceratopsid.[7][8][9] Others have synonymizedC. nasicornus withC. apertus,[10] or considered it a separateCentrosaurus species:Centrosaurus nasicornus.[11] It has also been suggested as the direct ancestor ofStyracosaurus albertensis.[12] A 2014 study of changes during growth inCentrosaurus concluded thatC. nasicornus is a junior synonym ofC. apertus, representing a middle growth stage.[13]
The speciesC. brinkmani, described in 2005, was moved to the new genusCoronosaurus in 2012.[14]
Centrosaurus were large dinosaurs, although not as large as some of their relatives, reaching 5–5.5 metres (16–18 ft) long and 2–2.5 metric tons (2.2–2.8 short tons) in body mass situated atop stocky limbs.[15][16] Like other centrosaurines,Centrosaurus bore a single large horn over their noses.[2] These horns curved forwards or backwards depending on the specimen. Skull ornamentation was reduced as animals aged.[13] 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.[13]
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 ofCentrosaurus were moderately long, with fairly largefenestrae and small hornlets along the outer edges.[2]
The genusCentrosaurus gives its name to the Centrosaurinae subfamily. Its closest relatives appear to beStyracosaurus andMonoclonius. It so closely resembles the latter of these that some paleontologists have considered them to represent the same animal.[2] Other members of the Centrosaurinaesubfamily includePachyrhinosaurus,[17][18]Avaceratops,[17]Einiosaurus,[18][19]Albertaceratops,[19] andAchelousaurus.[18]
Thecladogram presented below represents a phylogenetic analysis by Chibaet al. (2017):[20]
| Centrosaurinae |
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Like otherceratopsids, the jaws ofCentrosaurus were adapted to shear through tough plant material. The discovery of gigantic bone beds ofCentrosaurus in Canada suggest that they were gregarious animals and could have traveled in large herds.[2] A bone bed composed ofCentrosaurus andStyracosaurus remains is known from theDinosaur Park Formation in what is now Alberta.[21] The mass deaths may have been caused by otherwise non-herding animals gathering around a waterhole during a drought.[22]Centrosaurus is found lower in the formation thanStyracosaurus, indicating thatCentrosaurus was displaced byStyracosaurus as the environment changed over time.[5]
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 ofTriceratops andCentrosaurus 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 ofCentrosaurus were too thin to be used for defense against predators, although the thicker, solid frills ofTriceratops might have evolved to protect their necks. The frills ofCentrosaurus were most likely used "for species recognition and/or other forms of visual display".[23]
A specimen ofCentrosaurus apertus recovered from Dinosaur Provincial Park in 1989 was discovered to have cripplingosteosarcoma in its right fibula. Examination of the cancerous lesions in the bone suggest thecancer 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 theCentrosaurus 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 theCentrosaurus bone bed where it was found. The specimen remains one of the few dinosaur specimens found with severe cancer.[24]
Thomas M. Lehman has observed thatCentrosaurus fossils haven't been found outside of southernAlberta even though they are among the most abundantJudithian dinosaurs in the region.[25] 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.[25] This restricted distribution strongly contrasts with modernmammalian faunas whose large herbivores' ranges "typical[ly] ... span much of a continent."[25] Fossil material ofC. apertus was subsequently described from the strata of the Dinosaur Park Formation inSaskatchewan.[26]
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