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Triceratops (IPA: /tɹaɪ'sɛɹətɒps/) meaning 'three-horned face' (derived from the Greek tri -/τρι- meaning 'three', ceras/κέρας meaning 'horn' and -ops/ωψ meaning 'face') was a herbivorous genus of ceratopsid dinosaur that lived during the late Maastrichtian (end of the Late Cretaceous Period) around 68-65 million years ago in what is now North America. It was one of the last dinosaurs to appear before the great extinction.

Although no complete skeleton has been found, Triceratops is well known from numerous specimens collected since its discovery in 1889. Its four-legged horned appearance, somewhat reminiscent of an ancient rhinoceros, is one of the most recognized of all dinosaurs.

Description

It has been estimated that Triceratops reached about 8 m (26 ft) long, 3 m (10 ft) tall, and weighed several tonnes. The most distinctive feature is its large skull, one of the largest of all land animals. It can be over 2 m in length,Cite error: A <ref> tag is missing the closing </ref> (see the help page). It bears a single horn on the snout, above the nostrils and a pair of horns approximately 1 m (3 ft, 4 in) long, above the eyes. To the rear of the skull is a relatively short bony frill. Most other frilled dinosaurs had large fenestrae in their frills, while the frill of Triceratops is noticeably solid.

Triceratops possessed a sturdy build, with robust limbs, and short five-hoofed hands and four-hoofed feet. Although certainly quadrupedal, the posture of Triceratops has long been the subject of some debate. Originally, it was believed that the front legs of the animal had to be sprawling at angles from the thorax, in order to better bear the weight of the head. This stance can be seen in paintings by Charles Knight and Rudolph Zallinger. However, ichnological evidence in Triceratops trackways, and recent reconstructions of skeletons (both physically and digitally), seem to show that Triceratops maintained an upright stance during normal locomotion, with the elbows slightly bowed out, in an intermediate state between fully upright and fully sprawling (as in the modern rhinoceros). This does not preclude a sprawling gait for confrontations or feeding.

Classification

Triceratops is the best known and one of the last members of the Ceratopsidae, a family of large North American horned dinosaurs. The exact location of Triceratops among the ceratopsians has been debated over the years. Confusion stemmed mainly from the short, solid frill (similar to that of centrosaurines), and the long brow horns (more akin to chasmosaurines). In the first overview of horned dinosaurs in 1907, R. S. Lull hypothesized two lineages, one of Monoclonius and Centrosaurus preceding Triceratops, the other with Ceratops and Torosaurus. Later revisions supported this view, describing the first group the short-frilled ceratopsians (with Triceratops) and the latter as the long-frilled.

In 1949, C. M. Sternberg was the first to question this and favoured instead that Triceratops was more closely related to Arrhinoceratops and Chasmosaurus based on skull and horn features. However he was largely ignored with Ostrom and later David Norman, placing Triceratops within Centrosaurinae.

Subsequent discoveries and analyses upheld Sternberg's view of the position of Triceratops, with Lehman defining both subfamilies in 1990 and diagnosing Triceratops as a chasmosaurine on the basis of several morphological features. In fact, it fit well into the chasmosaurine subfamily, apart from its one feature of a shortened frill. Further research by Peter Dodson, both a 1990 cladistic analysis and a 1993 RFTRA analysis, which systematically measures similarities in skull shape, reinforce Triceratops' place.

Origins

For many years the origins of Triceratops have been largely obscure. In 1922, the newly discovered Protoceratops was seen as its ancestor by Henry Fairfield Osborn, but many decades before more findings came to light. However, recent years have been fruitful for the discovery of several dinosaurs related to ancestors of Triceratops; Zuniceratops, the first horned Ceratopsian in the late 1990s, and Yinlong, the first Jurassic Ceratopsian, from 2005. These dinosaur finds have been vital in illustrating the origins of horned dinosaurs in general in Asia in the late Jurassic and early Cretaceous, and the lineage of Triceratops for at least 10 million years in North America.

Discoveries and species

Triceratops was discovered by John Bell Hatcher, in 1888. It was only determined to be a dinosaur when an intact skull was found. Othniel Charles Marsh in 1887 near Denver, Colorado, USA, misidentified Triceratops as a type of bison; giving it the name Bison alticornis. However, in 1889 when the intact skull was described by Marsh, he erected the generic name Triceratops. The sturdy nature of the animal's skull has ensured that many examples have been preserved as fossils, allowing variations between species and individuals to be studied. Triceratops remains have subsequently been found in Montana, South Dakota, and Wyoming, in the USA and in Saskatchewan and Alberta, in Canada.

How many species?

In the first decades after Triceratops was described, various skulls were collected, which varied to a lesser or greater degree from the original Triceratops, named T. horridus by Marsh (from Latin horridus; "rough, rugose", suggesting the roughened texture of those bones belonging to the type specimen). This variation is unsurprising, given that Triceratops skulls are large three-dimensional objects, coming from individuals of different ages and both sexes, and which were subjected to different amounts and directions of pressure during fossilization. Discoverers would name these up as separate species (listed below), and came up with several phylogenetic schemes for how they were related to each other.

In the first attempt to understand the many species, Lull found two groups, although he did not say how he distinguished them: one composed of T. horridus, T. prorsus, and T. brevicornus; one of T. elatus and T. calicornis; and two species (T. serratus and T. flabellatus) that stood apart. By 1933, and his revision of the Hatcher-Marsh-Lull monograph, he retained his two groups and two unaffiliated species, with a third lineage of T. obtusus and T. hatcheri that was characterized by a very small nasal horn. T. horridus-T. prorsus-T. brevicornus was now thought to be the most conservative lineage, with an increase in skull size and a decrease in nasal horn size, and T.-elatus-T. calicornis was defined by large brow horns and small nasal horn. Sternberg made one modification, adding T. eurycephalus and suggesting that it linked the second and third lineages closer together than they were to the T. horridus lineage. This pattern was followed until the major studies of the 1980s and 1990s.

Eventually, however, the idea that the differing skulls might be representative of individual variation within one (or two) species gained popularity. In 1986, Ostrom and Wellnhofer published a paper where they proposed there was only one species - Triceratops horridus. Part of their rationale is that generally there are only one or two species of any large animal in a region (e.g. elephant or giraffe in modern Africa). To their findings, Lehman added the old Lull-Sternberg lineages combined with maturity and sexual dimorphism, suggesting that the T. horridus-T. prorsus-T. brevicornus lineage was composed of females, the T.calicornis-T.elatus lineage was made up of males, and the T. obtusus-T. hatcheri lineage was of pathologic old males. His reasoning was that males had taller, more erect horns, and larger skulls, and females had smaller skulls with shorter, forward-facing horns.

These findings, however, were contested a few years later by Catherine Forster, who reanalysed Triceratops material more comprehensively and concluded that the remains fell into two species, T. horridus and T. prorsus, although the distinctive skull of T. (now tentatively Diceratops) hatcheri differed enough to warrant a separate genus. She found that T. horridus and several other species grouped together, and T. prorsus and T. brevicornius stood alone, and since there were many more specimens in the first group, she suggested that this meant the two groups were two species. One can still interpret this as two sexes, though.

Valid species

• T. horridus Marsh, 1889 (type species)
• T. prorsus Marsh, 1890

Doubtful species (Nomina dubia)

• T. albertensis Sternberg, 1949
• T. alticornis Marsh, 1887 (originally 'Bison')
• T. eurycephalus Schlaikjer, 1935
• T. galeus Marsh, 1889
• T. ingens Lull, 1915
• T. maximus Brown, 1933
• T. sulcatus Marsh, 1890

Misassignments

• T. brevicornis Hatcher, 1905 (=T. prorsus)
• T. calicornus Marsh, 1898 (=T. horridus)
• T. elatus Marsh, 1891 (=T. horridus)
• T. flabellatus Marsh, 1889 (=T. horridus)
• T. hatcheri Lull, 1907 (=Diceratops hatcheri)
• T. mortuarius Cope, 1874 (nomen dubium; originally Polyonax; =Polyonax mortuarius)
• T. obtusus Marsh, 1898 (=T. horridus)
• T. serratus Marsh, 1890 (=T. horridus)
• T. sylvestris Cope, 1872 (nomen dubium; originally Agathaumas; =Agathaumas sylvestris)

Paleobiology

Although Triceratops is commonly portrayed as a herding animal, there is currently no solid evidence that it lived in herds. Unlike other horned dinosaurs, some of which are known from sites preserving dozens or hundreds of individuals, all Triceratops finds known at present preserve only solitary individuals. However, its remains are very common; for example, in the Hell Creek Formation of Montana, Science Museum of Minnesota paleontologist Bruce Erickson has reported to have seen 200 specimens of T. prorsus. Similarly, Barnum Brown claimed to have seen over 500 skulls in the field. Because Triceratops teeth, horn fragments, frill fragments, and other skull fragments are such abundant fossils in the Lancian faunal stage of the late Maastrichtian (68-65 mya) (late Cretaceous) Period of western North America, it is regarded as among the dominant herbivores of the time. (see for example commentary at )

Dentition and Diet

Triceratops was herbivorous, and because of its low head, its primary food was probably low growth, although it may have been able to knock down taller plants with its horns, beak, and bulk. The jaws were tipped with deep, narrow beaks, believed to have been better at grasping and plucking than biting. As in the case of the primitive horned dinosaur Protoceratops locked in combat with Velociraptor, this beak may also be have been used in self-defense.

The teeth of Triceratops were arranged in batteries of 36 to 40 columns with 3 to 5 stacked teeth per column, depending on the size of the animal. This gives a total of 432 to 800 teeth, of which only a fraction were in use at any given time (tooth replacement was continuous and occurred throughout the life of the animal). They functioned in a vertical to near-vertical shearing configuration. Like all ceratopsid teeth, the roots are split, making them very distinctive fossils.

Functions of the horns and frill

There has been much speculation over the functions of Triceratops' head adornments. The two main theories have revolved around use in combat, or display in courtship, with the latter thought now to be the most likely primary function.

Early on, Lull postulated that the frill may have served as anchor points for the jaw muscles to aid in chewing. This has been put forward by other authors over the years but later study does not find evidence of large muscle attachments on the frill bones.

Triceratops has long been thought to have possibly used its horns and frill in combat with predators such as Tyrannosaurus, the idea being discussed by C.H. Sternberg in 1917 and 70 years later by Robert Bakker.

In 2005, a BBC documentary, The Truth About Killer Dinosaurs, tested how Triceratops might have defended itself against large predators like Tyrannosaurus. To see if Triceratops could have charged other dinosaurs, as would a modern-day rhinoceros, an artificial Triceratops skull was made and propelled into simulated Tyrannosaurus skin, at 24 km/h (15 mph). The brow horns penetrated the skin, but the blunt nose horn and the beak could not, and the front of the skull broke. The conclusion drawn was that it would have been impossible for Triceratops to have defended itself in this way - instead it probably stood its ground when attacked by large predators, using its horns for goring if the predator came close enough.

Related to combat with predators using horns, Triceratops are classically shown engaging each other in combat with horns locked. While studies show that such activity would be feasible, if unlike that of present-day horned animals, there is no evidence that they actually did do so. Additionally, although pitting, holes, lesions, and other damage on Triceratops skulls (and the skulls of other ceratopsids) is often attributed to horn damage in combat, recent study finds no evidence for horn thrust injuries causing these forms of damage (for example, there is no evidence for infection or healing). Instead, non-pathological bone resorption, or unknown bone disease, are suggested as causes.

A recent study of the smallest Triceratops skull, ascertained to be a juvenile, shows the frills and horns developed at a very early age, predating sexual development and thus possibly important for visual communication and species recognition. The large eyes and shortened features - a hallmark of "cute" baby mammals - also suggest that the parent Triceratops may have cared for its young.

The thoery of their use in sexual display was first highlighted by Davitashvili in 1961 and has gained increasing acceptance since. Evidence that display either in courtship or in other social behaviour can be seen in the fact that horned dinosaurs differ markedly in their adornments, making each species highly distinctive. Also, modern living creatures with such displays of horns and adornments use them in similar behaviour.

Another theory is that the large frill served to increase body area, to regulate body temperature (see also: thermoregulation). However, this alone would not account for the differences between species.

A final idea is that the frill helped to amplify and\or receive low-frequency sounds.

Depiction in popular media

The distinctive appearance of Triceratops has led to it being frequently depicted in various forms of popular culture including films, computer games and documentaries.It is famously known as "three-horns" due to the three prominent horns on its head and nose, which have become almost synonymous with the dinosaur. The shorthand "Trike" is another common informal name (see for example the archives of the Dinosaur Mailing List). Triceratops is also the official state fossil of South Dakota, and the official state dinosaur of Wyoming.

References

1. Liddell & Scott (1980). Greek-English Lexicon, Abridged Edition. Oxford University Press, Oxford, UK. ISBN 0-19-910207-4.
2. Lehman T.M. (1987). Late Maastrichtian paleoenvironments and dinosaur biogeography in the Western Interior of North America. Paleogeography, Paleoacclimatology and Paleoecology. 60:189-217.
3. Lambert D (1993). The Ultimate Dinosaur Book. Dorling Kindersley, New York. pp. 110–129. ISBN 1-56458-304-X.
4. ^ Dodson, P. (1996). The Horned Dinosaurs. Princeton University Press:Princeton, New Jersey, 346 pp.
5. ^ 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. p. 494-513.
6. Christiansen, P., and Paul, G.S. (2001). Limb bone scaling, limb proportions, and bone strength in neoceratopsian dinosaurs. Gaia 16:13-29.
7. Chapman, R.E., Snyder, R.A., Jabo, S., and Andersen, A. (2001). On a new posture for the horned dinosaur Triceratops. Journal of Vertebrate Paleontology 21 (Supplement to Number 3), Abstracts of Papers, 61st Annual Meeting:39A-40A.
8. ^ Hatcher, J. B., Marsh, O. C. and Lull, R. S. 1907. The Ceratopsia. Government Printing Office, Washington, D.C., 300 pp
9. ^ Lull,R.S. 1933. A revision of the Ceratopsia or horned dinosaurs. Memoirs of the Peabody Museum of Natural History 3(3):1-175
10. ^ Sternberg, C. M. 1949. The Edmonton fauna and description of a new Triceratops from the Upper Edmonton member; phylogeny of the Ceratopsidae. National Museum of Canada Bulletin 113 33-46
11. Ostrom, J. H. 1966. Functional morphology and evolution of the ceratopsian dinosaurs. Evolution 20:220-227
12. David Norman, John Sibbick. The Illustrated Encyclopedia of Dinosaurs. Salamander Books, 1985
13. ^ Lehman, T. M. 1990. The ceratopsian subfamily Chasmosaurinae: sexual dimorphism and systematics. K. Carpenter & P. J. Currie (eds.), Dinosaur Systematics: Perspectives and Approaches, Cambridge University Press, Cambridge 211-229
14. Dodson, P. & Currie, P. J., 1990: Neoceratopsia. 593-618. in Weishampel, D. B., Dodson, P., & Osmólska, H. (eds.), 1990: The Dinosauria.
15. Dodson, P. (1993): Comparative Craniology of the Ceratopsia. In: American Journal of Science 293, pp 200-234.
16. Dodson, P. (1996). The Horned Dinosaurs. Princeton University Press, Pinceton, New Jersey, p. 244.
17. Ostrom, J. H., and P. Wellnhofer. 1986. The Munich specimen of Triceratops with a revision of the genus. Zitteliana 14: 111 - 158.
18. Forster CA (1996): Species resolution in Triceratops: cladistic and morphometric approaches. J.Vert.Paleont. 16(2): 259-270
19. 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.
20. Erickson, B.R. 1966. Mounted skeleton of Triceratops prorsus in the Science Museum. Scientific Publications of the Science Museum 1:1-16.
21. Dodson, P. (1996). The Horned Dinosaurs. Princeton University Press, Princeton, New Jersey, p. 79
22. Ostrom, J.H. (1966). Functional morphology and evolution of the ceratopsian dinosaurs. Evolution 20:290-308.
23. Carpenter, K. (1998). Evidence of predatory behavior by carnivorous dinosaurs. Gaia 15: 135-144.
24. Lull, R.S. (1908). The cranial. musculature and the origin of the frill in the ceratopsian dinosaurs. American Journal of Science 4(25):387-399.
25. ^ 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.
26. Sternberg, C. H. 1917. Hunting Dinosaurs in the Badlands of the Red Deer River, Alberta, Canada. Published by the author, San Diego, Calif., 261 pp
27. Bakker, R. T. 1986. The Dinosaur Heresies: New Theories Unlocking The Mystery of the Dinosaurs and Their Extinction. William Morrow, New York. 481pp ISBN 0140100555
28. Farke, A.A. (2004). Horn Use in Triceratops (Dinosauria: Ceratopsidae): Testing Behavioral Hypotheses Using Scale Models. Palaeo-electronica.
29. Tanke, D.H, and Farke, A.A. (2006). Bone resorption, bone lesions, and extracranial fenestrae in ceratopsid dinosaurs: a preliminary assessment. in: Carpenter, K (ed.). Horns and Beaks: Ceratopsian and Ornithopod Dinosaurs Indiana University Press: Bloomington. 319-347.
30. Goodwin, M.B., Clemens, W.A., Horner, J.R., and Padian, K. (2006). The smallest known Triceratops skull: new observations on ceratopsid cranial anatomy and ontogeny. Journal of Vertebrate Paleontology 26(1):103-112.
31. Davitashvili L (1961). The Theory of sexual selection. Izdatel'stvo Akademia nauk SSSR. p. 538.
32. Farlow, J.O., and Dodson, P. 1975. The behavioral significance of frill and horn morphology in ceratopsian dinosaurs. Evolution, 29:353-361.
33. Wheeler, P.E. (1978). Elaborate CNS cooling structures in large dinosaurs. Nature 275:441–443.
34. Anton, in prep.; http://dml.cmnh.org/2000Nov/msg00543.html

• An excellent general overview, although slightly dated, is: Dodson, P. (1996). The Horned Dinosaurs. Princeton University Press: Princeton, New Jersey, pp. xiv-346.

External links

• Triceratops (short summary and good color illustration)
• Triceratops For Kids (a fact sheet about the Triceratops with activities for kids)
• Smithsonian Exhibit
• Triceratops Skull Picture
• post on Triceratops stance

• Ceratopsians
• Cretaceous dinosaurs
• North American dinosaurs
• Jurassic Park species