CERATOPSIA

'Ceratopsia' or 'Ceratopia' (Greek: "horned faces") is a group of herbivorous, beaked dinosaurs which thrived in what are now North America and Asia, during the Cretaceous Period, although ancestral forms lived earlier, in the Jurassic. Early members such as ''Psittacosaurus'' were small and bipedal. Later members, including ceratopsids like ''Centrosaurus'' and ''Triceratops'', became very large quadrupeds and developed elaborate facial horns and a neck frill. While the frill might have served to protect the vulnerable neck from predators, it may also have been used for display, thermoregulation, the attachment of large neck and chewing muscles or some combination of the above. Ceratopsians ranged in size from 1 meter (3 feet) and 23 kilograms (50 pounds) to over 9 m (30 ft) and 5,400 kg (12,000 lb).
''Triceratops'' is by far the best-known ceratopsian to the general public. It is traditional for ceratopsian genus names to end in "''-ceratops''", although this is not always the case. One of the first named genera was ''Ceratops'' itself, which lent its name to the group, although it is considered a ''nomen dubium'' today as it has no distinguishing characteristics that are not also found in other ceratopsians.^[1]

Contents

Anatomy

Taxonomy

Phylogeny

Paleobiology

Biogeography

Individual variation

Ecological role

References

External links

Anatomy

Ceratopsians are easily recognized by features of the skull. On the tip of a ceratopsian upper jaw is the rostral bone, a unique bone found nowhere else in the animal kingdom. Along with the predentary bone, which forms the tip of the lower jaw in all ornithischians, the rostral forms a superficially parrot-like beak. Also, the jugal bones below the eye are very tall and flare out sideways, making the skull appear somewhat triangular when viewed from above. This triangular appearance is accentuated, in later ceratopsians, by the rearwards extension of the parietal and squamosal bones of the skull roof, to form the neck frill.^[2]Dodson, P., Forster, C.A., & Sampson, S.D. 2004. Ceratopsidae. In: Dodson, P., Weishampel, D.B., & Osmolska, H. (Eds.). ''The Dinosauria'' (2nd Edition). Berkeley: University of California Press. Pp. 494-513.

Taxonomy

Ceratopsia was coined by Othniel Charles Marsh in 1890 to include dinosaurs possessing certain characteristic features, including horns, a rostral bone, teeth with two roots, fused neck vertebrae, and a forward-oriented pubis. Marsh considered the group distinct enough to warrant its own suborder within Ornithischia.^[3] The name is derived from the Greek ''κερας''/''keras'' meaning 'horn' and ''οψις''/''opsis'' meaning 'face'. As early as the 1960s, it was noted that the name ''Ceratopsia'' is actually incorrect linguistically and that it should be ''Ceratopia''.^[4] However, this spelling, while technically correct, has been used only rarely in the scientific literature and the vast majority of paleontologists continue to use Ceratopsia. As the ICZN does not govern taxa above the level of superfamily, this is unlikely to change.



Following Marsh, Ceratopsia has usually been classified as a suborder within the order Ornithischia, though occasionally it has been reduced to the level of infraorder.^[5]
Following is a list of ceratopsian genera by classification and location:

★ 'Infraorder Ceratopsia'

★
★ ''Yinlong'' - (Xinjiang, western China)

★
★ 'Family Chaoyangsauridae'

★
★
★ ''Xuanhuaceratops'' - (Hebei, China)

★
★
★ ''Chaoyangsaurus'' - (Liaoning, northeastern China)

★
★ 'Family Psittacosauridae'

★
★
★ ''Psittacosaurus'' - (China & Mongolia)

★
★
★ ''Hongshanosaurus'' - (Liaoning, northeastern China)

★
★ ''Liaoceratops'' - (Liaoning, northeastern China)

★
★ ''Yamaceratops'' - (Mongolia)

★
★ ''Archaeoceratops'' - (Gansu, northwestern China)

★
★ ''Auroraceratops'' - (Gansu, northwestern China)

★
★ 'Family Leptoceratopsidae'

★
★
★ ''Bainoceratops'' - (Mongolia)

★
★
★ ''Leptoceratops'' - (Alberta, Canada & Wyoming, USA)

★
★
★ ''Montanoceratops'' - (Montana, USA)

★
★
★ ''Prenoceratops'' - (Montana, USA)

★
★
★ ''Udanoceratops'' - (Mongolia)

★
★ 'Family Protoceratopsidae'

★
★
★ ''Graciliceratops'' - (Mongolia)

★
★
★ ''Bagaceratops'' - (Mongolia)

★
★
★ ''Breviceratops'' - (Mongolia)

★
★
★ ''Lamaceratops'' - (Mongolia)

★
★
★ ''Magnirostris'' - (Inner Mongolia, China)

★
★
★ ''Platyceratops'' - (Mongolia)

★
★
★ ''Protoceratops'' - (Mongolia)

★
★ 'Superfamily Ceratopsoidea'

★
★
★ ''Zuniceratops'' - (New Mexico, USA)

★
★
★ 'Family Ceratopsidae'
There are several fragmentary Asian forms which may or may not be valid: ''Asiaceratops'', ''Kulceratops'', ''Microceratops'', and ''Turanoceratops''. Possible ceratopsians from the Southern Hemisphere include the Australian ''Serendipaceratops'', known from an ulna, and ''Notoceratops'' from Argentina is known from a single toothless jaw (which has been lost).^[6]

Phylogeny

Paleontologists today agree on the overall structure of the ceratopsian family tree, although there are differences on individual taxa. There have been several cladistic studies performed on basal ceratopsians since 2000. None have used every taxon listed above and many of the differences between the studies are still unresolved.
In clade-based phylogenetic taxonomy, Ceratopsia is often defined to include all marginocephalians more closely related to ''Triceratops'' than to ''Pachycephalosaurus''.^[7] Under this definition, the most basal known ceratopsians are ''Yinlong'', from the Late Jurassic Period, along with ''Chaoyangsaurus'' and the family Psittacosauridae, from the Early Cretaceous Period, all of which were discovered in northern China or Mongolia. The rostral bone and flared jugals are already present in all of these forms, indicating that even earlier ceratopsians remain to be discovered.
The clade 'Neoceratopsia' includes all ceratopsians more derived than psittacosaurids. Another subset of neoceratopsians is called 'Coronosauria', which currently includes all ceratopsians more derived than ''Auroraceratops''. Coronosaurs show the first development of the neck frill and the fusion of the first several neck vertebrae to support the increasingly heavy head. Within Coronosauria, three groups are generally recognized, although the membership of these groups varies somewhat from study to study and some animals may not fit in any of them. One group can be called 'Protoceratopsidae' and includes ''Protoceratops'' and its closest relatives, all Asian. Another group, 'Leptoceratopsidae', includes mostly North American animals that are more closely related to ''Leptoceratops''. The 'Ceratopsoidea' includes animals like ''Zuniceratops'' which are more closely related to the family 'Ceratopsidae'. This last family includes ''Triceratops'' and all the large North American ceratopsians and is further divided into the subfamilies 'Centrosaurinae' and 'Ceratopsinae' (also known as 'Chasmosaurinae').
'Xu/Makovicky/Chinnery Phylogeny:'

Xu Xing of the Chinese Institute of Vertebrate Paleontology and Paleoanthropology (IVPP) in Beijing, along with Peter Makovicky, formerly of the American Museum of Natural History (AMNH) in New York City and others, published a cladistic analysis in the 2002 description of ''Liaoceratops''.Xu X., Makovicky, P.J., Wang X., Norell, M.A., You H. 2002. A ceratopsian dinosaur from China and the early evolution of Ceratopsia. ''Nature'' 416: 314-317. This analysis is very similar to one published by Makovicky in 2001.^[8] Makovicky, who currently works at the Field Museum of Natural History in Chicago, also included this analysis in his 2002 doctoral thesis. Xu and other colleagues added ''Yinlong'' to this analysis in 2006.^[9]
Brenda Chinnery, formerly of the Museum of the Rockies in Bozeman, Montana, independently described ''Prenoceratops'' in 2005 and published a new phylogeny.Chinnery, B. 2005. Description of ''Prenoceratops pieganensis'' gen. et sp. nov. (Dinosauria: Neoceratopsia) from the Two Medicine Formation of Montana. ''Journal of Vertebrate Paleontology'' 24(3): 572–590. In 2006, Makovicky and Mark Norell of the AMNH incorporated Chinnery's analysis into their own and also added ''Yamaceratops'', although they were not able to include ''Yinlong''.^[10] The cladogram presented below is a combination of Xu, Makovicky, and their colleagues' most recent work.
''Chaoyangsaurus'' is recovered in a more basal position than Psittacosauridae, although Chinnery's original analysis finds it within Neoceratopsia. Protoceratopsidae is considered to be the sister group of Ceratopsoidea. The fragmentary ''Asiaceratops'' was included in these studies and is found to have a variable position, either as a basal neoceratopsian or as a leptoceratopsid, most likely due to the amount of missing information. Removal of ''Asiaceratops'' stabilizes the entire cladogram.
Makovicky's latest analysis includes IVPP V12722 ("Xuanhuasaurus"), a Late Jurassic ceratopsian from China that at the time was awaiting publication, but has since been published as ''Xuanhuaceratops''. ''Kulceratops'' and ''Turanoceratops'' are considered ''nomina dubia'' in this study. Makovicky believes ''Lamaceratops'', ''Magnirostris'', and ''Platyceratops'' to be junior synonyms of ''Bagaceratops'', and ''Bainoceratops'' to be synonymous with ''Protoceratops''.
'You/Dodson Phylogeny:'

You Hailu of Beijing's Chinese Academy of Geological Sciences, was a co-author with Xu and Makovicky in 2002 but, in 2003, he and Peter Dodson from the University of Pennsylvania published a separate analysis.You H. & Dodson, P. 2003. Redescription of neoceratopsian dinosaur ''Archaeoceratops'' and early evolution of Neoceratopsia. ''Acta Palaeontologica Polonica'' 48(2): 261–272. The two presented this analysis again in 2004.^[2] In 2005, You and three others, including Dodson, published on ''Auroraceratops'' and inserted this new dinosaur into their phylogeny.^[12]
In contrast to the previous analysis, You and Dodson find ''Chaoyangsaurus'' to be the most basal neoceratopsian, more derived than ''Psittacosaurus'', while Leptoceratopsidae, not Protoceratopsidae, is recovered as the sister group of Ceratopsidae. This study includes ''Auroraceratops'' but lacks seven taxa found in Xu and Makovicky's work, so it is unclear how comparable the two studies are. ''Asiaceratops'' and ''Turanoceratops'' are each considered ''nomen dubium'' and not included. Along with Dong Zhiming, You described ''Magnirostris'' in 2003, but to date has not included it any of his cladograms.^[13]

Paleobiology

Biogeography

Ceratopsia appears to have originated in Asia, as all of the earliest members are found there. Fragmentary remains, including teeth, which appear to be neoceratopsian, are found in North America from the Albian stage (112 to 100 million years ago), indicating that the group had dispersed across what is now the Bering Strait by the middle of the Cretaceous Period.^[14] Almost all leptoceratopsids are North American, aside from ''Udanoceratops'', which may represent a separate dispersal event, back into Asia. Ceratopsids and their immediate ancestors, such as ''Zuniceratops'', are not found in Asia or any other continent and appear to be endemic to western North America. However, if ''Notoceratops'' and ''Serendipaceratops'' are indeed ceratopsians, this hypothesis will be significantly affected.

Individual variation

Unlike almost all other dinosaur groups, skulls are the most commonly preserved elements of ceratopsian skeletons and many species are known only from skulls. There is a great deal of variation between and even within ceratopsian species. Complete growth series from embryo to adult are known for ''Psittacosaurus'' and ''Protoceratops'', allowing the study of ontogenetic variation in these species.^[15]Dodson, P. 1976. Quantitative aspects of relative growth and sexual dimorphism in ''Protoceratops''. ''Journal of Paleontology'' 50: 929-940. Significant sexual dimorphism has been noted in ''Protoceratops'' and several ceratopsids.^[16]

Ecological role

''Psittacosaurus'' and ''Protoceratops'' are the most common dinosaurs in the different Mongolian sediments where they are found. ''Triceratops'' fossils are far and away the most common dinosaur remains found in the latest Cretaceous rocks in the western United States, making up as much as 5/6ths of the large dinosaur fauna in some areas.Bakker, R.T. (1986). ''The Dinosaur Heresies: New Theories Unlocking The Mystery of the Dinosaurs and Their Extinction''. William Morrow:New York, p. 438. ISBN 0140100555 These facts indicate that some ceratopsians were the dominant herbivores in their environments.
Some species of ceratopsians, especially ''Centrosaurus'' and its relatives, appear to have been gregarious, living in herds. This is suggested by bonebed finds with the remains of many individuals of different ages. Like modern migratory herds, they would have had a significant effect on their environment, as well as serving as a major food source for predators.

References

1. Dodson, P. 1996. ''The Horned Dinosaurs''. Princeton: Princeton University Press. 346pp.
2. You H. & Dodson, P. 2004. Basal Ceratopsia. In: Weishampel, D.B., Dodson, P., & Osmolska, H. (Eds.). ''The Dinosauria'' (2nd Edition). Berkeley: University of California Press. Pp. 478-493.
3. Marsh, O.C. (1890). "Additional characters of the Ceratopsidae, with notice of new Cretaceous dinosaurs." ''American Journal of Science'', '39': 418-429.
4. Steel, R. 1969. Ornithischia. In: Kuhn, O. (Ed.). ''Handbuch de Paleoherpetologie'' (Part 15). Stuttgart: Gustav Fischer Verlag. 87pp.
5. Benton, M.J. (2004). 'Vertebrate Palaeontology, Third Edition''. Blackwell Publishing, 472 pp.
6. Rich, T.H. & Vickers-Rich, P. 2003. Protoceratopsian? ulnae from the Early Cretaceous of Australia. ''Records of the Queen Victoria Museum.'' No. 113.
7. Sereno, P.C. 1998. A rationale for phylogenetic definitions, with applications to the higher-level taxonomy of Dinosauria. ''Neues Jahrbuch fur Geologie und Palaontologie: Abhandlungen'' 210: 41-83.
8. Makovicky, P.J. 2001. A ''Montanoceratops cerorhynchus'' (Dinosauria: Ceratopsia) braincase from the Horseshoe Canyon Formation of Alberta, In: Tanke, D.H. & Carpenter, K. (Eds.). ''Mesozoic Vertebrate Life''. Bloomington: Indiana University Press. Pp. 243-262.
9. Xu X., Forster, C.A., Clark, J.M., & Mo J. 2006. A basal ceratopsian with transitional features from the Late Jurassic of northwestern China. ''Proceedings of the Royal Society B: Biological Sciences''. 273: 2135-2140
10. Makovicky, P.J. & Norell, M.A. 2006. ''Yamaceratops dorngobiensis'', a new primitive ceratopsian (Dinosauria: Ornithischia) from the Cretaceous of Mongolia. ''American Museum Novitates'' 3530: 1-42.
11. You H. & Dodson, P. 2004. Basal Ceratopsia. In: Weishampel, D.B., Dodson, P., & Osmolska, H. (Eds.). ''The Dinosauria'' (2nd Edition). Berkeley: University of California Press. Pp. 478-493.
12. You H., Li D., Lamanna, M.C., & Dodson, P. 2005. On a new genus of basal neoceratopsian dinosaur from the Early Cretaceous of Gansu Province, China. ''Acta Geologica Sinica'' (English edition) 79(5): 593-597.
13. You H. & Dong Z. 2003. A new protoceratopsid (Dinosauria: Neoceratopsia) from the Late Cretaceous of Inner Mongolia, China. ''Acta Geologica Sinica'' (English edition). 77(3): 299-303.
14. Chinnery, B.J., Lipka, T.R., Kirkland, J.I., Parrish, J.M., & Brett-Surman, M.K. 1998. Neoceratopsian teeth from the Lower to Middle Cretaceous of North America. In: Lucas, S.G., Kirkland, J.I., & Estep, J.W. (Eds.). ''Lower and Middle Cretaceous Terrestrial Ecosystems''. ''New Mexico Museum of Natural History and Science Bulletin'' 14: 297-302.
15. Erickson, G.M. & Tumanova, T.A. 2000. Growth curve of ''Psittacosaurus mongoliensis'' Osborn (Ceratopsia: Psittacosauridae) inferred from long bone histology. ''Zoological Journal of the Linnean Society of London'' 130: 551-566.
16. Lehman, T.M. 1990. The ceratopsian subfamily Chasmosaurinae: sexual dimorphism and systematics. In: Carpenter, K. & Currie, P.J. (Eds.). ''Dinosaur Systematics: Approaches and Perspectives''. Cambridge: Cambridge University Press. Pp. 211-230.

External links

★ Introduction to the Ceratopsians, University of California Museum of Paleontology

★ Marginocephalia at Palaeos.com (technical)

★ Ceratopia, from ''Thescelosaurus!'' Web Site