Centrosaurus

Bilateria

Centrosaurus Temporal range: Late Cretaceous, 76.5–75.5 Ma PreЄ Є O S D C P T J K Pg N ↓
C. apertus skull, Museum of Victoria
Scientific classification
Phylum:	Chordata
Class:	Reptilia
Superorder:	Dinosauria
Order:	†Ornithischia
Suborder:	†Ceratopsia
Family:	†Ceratopsidae
Subfamily:	†Centrosaurinae
Genus:	†Centrosaurus
Type species
†Centrosaurus apertus Lambe, 1904
Species
C. apertus Lambe, 1904 C. brinkmani Ryan & Russell, 2005

Centrosaurus ( /ˌsɛtrɵˈsɔrəs/ sen-tro-sawr-əs) is a genus of herbivorous ceratopsian dinosaurs from the late Cretaceous of Canada. Their remains have been found in the Dinosaur Park Formation and uppermost Oldman Formation, dating from 76.5 to 75.5 million years ago.^[1]

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 their frills, not to 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.

Description

Life restoration of C. apertus

Skin impression

The massive bodies of Centrosaurus were borne by stocky limbs, although at up to 18–20 ft (6m) they was not particularly large dinosaurs. Like other centrosaurines, Centrosaurus bore single large horns over their noses.^[2] These horns curved forwards or backwards depending on the 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 frills of Centrosaurus were moderately long, with fairly large fenestrae and small hornlets along the outer edges.^[2]

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.

Discovery

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.^[2] 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.^[3]

Classification

The genus Centrosaurus gives its name to the Centrosaurinae subfamily. 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."^[4] 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.^[2]

C. apertus skull, Royal Ontario Museum

Other members of the Centrosaurinae clade include Pachyrhinosaurus,^[5][6] Avaceratops,^[5] Einiosaurus,^[6][7] Albertaceratops,^[7] Achelousaurus,^[6] and possibly Brachyceratops,^[8] 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.^[9] His assessments have been partially followed, with other researchers not accepting Monoclonius nasicornis as a female Styracosaurus, or Monoclonius as a valid genus.^[10] While sexual dimorphism has been proposed for an earlier ceratopsian, Protoceratops,^[11] there is no firm evidence for sexual dimorphism in any ceratopsid.^[12][13][14]

Palaeobiology

Life restoration of two fighting C. apertus

Like other ceratopsids, the jaws of Centrosaurus were adapted to shear through tough plant material; their frills provided an attachment for large jaw muscles. The discovery of gigantic bone beds of Centrosaurus in Canada suggest that they were gregarious animals and could have traveled in large herds.^[2] A bone bed composed of Centrosaurus and Styracosaurus remains is known from the Dinosaur Park Formation in what is now Alberta.^[15] The mass deaths may have been caused by otherwise non-herding animals gathering around a waterhole during a drought.^[16] Centrosaurus is found lower in the formation than Styracosaurus, indicating that Centrosaurus was displaced by Styracosaurus as the environment changed over time.^[10]

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".^[17]

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.^[18] 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.^[18] This restricted distribution strongly contrasts with modern mammalian faunas whose large herbivores' ranges "typical[ly] ... span much of a continent."^[18]

References

1. ^ Arbour, V. M.; Burns, M. E.; and Sissons, R. L. (2009). "A redescription of the ankylosaurid dinosaur Dyoplosaurus acutosquameus Parks, 1924 (Ornithischia: Ankylosauria) and a revision of the genus". Journal of Vertebrate Paleontology 29 (4): 1117–1135. doi:10.1671/039.029.0405. 
2. ^ ^{a b c d e} "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. ISBN 0-7853-0443-6.
3. ^ Scientists find dino deathbed, signs of carnage. Edmonton Sun. http://www.edmontonsun.com/news/canada/2010/06/18/14439211.html retrieved 18 06 2010
4. ^ Tweet, J. (2007). "Centrosaurinae". Thescelosaurus. Qwest.net. http://www.thescelosaurus.com/centrosaurinae.htm. Retrieved 2009-05-25. 
5. ^ ^{a b} Dodson, P. (1990). "On the status of the ceratopsids Monoclonius and Centrosaurus". In Carpenter, K.; and Currie, P.J. (eds.). Dinosaur Systematics: Perspectives and Approaches. Cambridge: Cambridge University Press. pp. 231–243. ISBN 0-521-36672-0. 
6. ^ ^{a b c} Ryan, M.J.; A.P. Russell (2005). "A new centrosaurine ceratopsid from the Oldman Formation of Alberta and its implications for centrosaurine taxonomy and systematics". Canadian Journal of Earth Sciences 42 (7): 1369–1387. doi:10.1139/e05-029. 
7. ^ ^{a b} Ryan, M.J. (2007). "A new basal centrosaurine ceratopsid from the Oldman Formation, southeastern Alberta". Journal of Paleontology 81 (2): 376–396. doi:10.1666/0022-3360(2007)81[376:ANBCCF]2.0.CO;2. 
8. ^ Dodson, P., Forster, C. A, and Sampson, S. D. (2004) Ceratopsidae. In: Weishampel, D. B., Dodson, P., and Osmólska, H. (eds.), The Dinosauria (second edition). University of California Press:Berkeley, pp. 494–513. ISBN 0-520-24209-2.
9. ^ Dodson, P. (1996). The Horned Dinosaurs: A Natural History. Princeton University Press: Princeton, New Jersey, pp. 197–199. ISBN 0-691-02882-6.
10. ^ ^{a b} Ryan, Michael J.; and Evans, David C. (2005). "Ornithischian Dinosaurs". In Currie, Phillip J., and Koppelhus, Eva. Dinosaur Provincial Park: A Spectacular Ancient Ecosystem Revealed. Bloomington: Indiana University Press. pp. 312–348. ISBN 0-253-34595-2. 
11. ^ Dodson, P. "Quantitative aspects of relative growth and sexual dimorphism in Protoceratops". Journal of Paleontology 50: 929–940. 
12. ^ 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.
13. ^ Lehman, T. M. (1998). "A gigantic skull and skeleton of the horned dinosaur Pentaceratops sternbergi from New Mexico". Journal of Paleontology 72 (5): 894–906. 
14. ^ Sampson, S. D.; Ryan, M.J.; and Tanke, D.H. (1997). "Craniofacial ontogeny in centrosaurine dinosaurs (Ornithischia: Ceratopsidae): taphonomic and behavioral phylogenetic implications". Zoological Journal of the Linnean Society 121 (3): 293–337. doi:10.1111/j.1096-3642.1997.tb00340.x. 
15. ^ Eberth, David A.; and Getty, Michael A. (2005). "Ceratopsian bonebeds: occurrence, origins, and significance". In Currie, Phillip J., and Koppelhus, Eva. Dinosaur Provincial Park: A Spectacular Ancient Ecosystem Revealed. Bloomington: Indiana University Press. pp. 501–536. ISBN 0-253-34595-2. 
16. ^ Rogers, R. R. (1990). "Taphonomy of three dinosaur bone beds in the Upper Cretaceous Two Medicine Formation, northwestern Montana: Evidence for drought-related mortality". PALAIOS (SEPM Society for Sedimentary Geology) 5 (5): 394–41. doi:10.2307/3514834. JSTOR 3514834. 
17. ^ Farke, A.A., Wolff, E.D.S., and Tanke, D.H. (2009) "Evidence of Combat in Triceratops". PLoS ONE 4(1): e4252. doi:10.1371/journal.pone.0004252
18. ^ ^{a b c} 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.

External links

Dinosaurs portal

• Centrosaurus, from the Dinosaur Encyclopaedia at Univ. of Illinois at Urbana-Champagne