Triceratops skeleton at the
National Museum of Natural History.
Triceratops 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 Maastrichtian (end of the Late Cretaceous Period) around 70-65 million years ago in what is now North America.
Although no complete skeleton has been found, Triceratops is well known from numerous specimens collected for over a century. Its four-legged horned appearance, somewhat reminiscent of an ancient rhinoceros, is one of the most recognized of all dinosaurs.
It has been estimated that Triceratops was about 9 m (30 ft) long, 3 m (10 ft) tall, and weighed around 5,400 kg (12,000 lb). The most distinctive feature is its large skull, one of the largest of all land animals. It can be over 2 m in length, and can reach almost a third of the length of the entire animal. 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.
Ceratopsian crest as acoustic amplifier can be found in published work:
Anton, J.A. Dinosaurs Incognito. 2009. VDM Verlag. Germany. pp. 192., since its short legs meant it could not take long strides. 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 Rudolf Zallinger. However, ichnological evidence in Triceratops trackways seem to show that Triceratops maintained an upright stance during normal locomotion, with the knees slightly bowed out (as in the modern rhinoceros). This does not preclude a sprawling gait for confrontations or feeding.
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 Triceratops position , 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.
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.
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, which Marsh later admitted were those of an aged individual). Discoverers would write these up as separate species (listed below). 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 the 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). A few years later, Catherine Forster 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.
- 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
- 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)
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; in fact the most common recovered from the Hell Creek Formation of Montana,where Bruce Erickson has reported to have seen 200 specimens of T. prorsus,  , and similar aged rocks in Saskatchewan and Wyoming - all these strata being the very youngest beds before the great extinction. As well, Barnum Brown claimed to have seen over 500 skulls in the field.
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. These teeth, along with horn, frill, and other skull fragments, are among the most abundant fossils in the late Maastrichtian (68-65 mya) (late Cretaceous) Period of western North America (see for example commentary at ), suggesting that it was one of the dominant herbivores of the time.
Functions of the horns and frill
There has been much speculation over the functions of Triceratops' head adornments.
A number of functions have been proposed for the frill:
- Defense against carnivores, such as Tyrannosaurus
- Communication between herd members
- Battling rival Triceratops over status, resources or territory
- Courtship display
- A status symbol which reflects (or determines) the individual's status in the herd
- Anchor points for the jaw muscles
- Increasing body area, to regulate body temperature (see also: thermoregulation)
- Amplifying and\or receiving low-frequency sounds 
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.
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.
Depiction in popular media
In popular culture, Triceratops 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. It is a common pop dinosaur.
- ↑ Liddell & Scott (1980). Greek-English Lexicon, Abridged Edition. Oxford University Press, Oxford, UK. ISBN 0-19-910207-4.
- ↑ 2.0 2.1 Lambert D (1993). The Ultimate Dinosaur Book. Dorling Kindersley, New York, 110-129. ISBN 1-56458-304-X.
- ↑ Dodson, P. (1996). The Horned Dinosaurs. Princeton University Press, Pinceton, New Jersey, 346pp
- ↑ Hatcher, J. B., Marsh, O. C. and Lull, R. S. 1907. The Ceratopsia. Government Printing Office, Washington, D.C., 300 pp
- ↑ Lull,R.S. 1933. A revision of the Ceratopsia or horned dinosaurs. Memoirs of the Peabody Museum of Natural History 3(3):1-175
- ↑ 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
- ↑ Ostrom, J. H. 1966. Functional morphology and evolution of the ceratopsian dinosaurs. Evolution 20:220-227
- ↑ David Norman, John Sibbick. The Illustrated Encyclopedia of Dinosaurs. Salamander Books, 1985
- ↑ 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
- ↑ Dodson, P. & Currie, P. J., 1990: Neoceratopsia. 593-618. in Weishampel, D. B., Dodson, P., & Osmólska, H. (eds.), 1990: The Dinosauria.
- ↑ Dodson, P. (1993): Comparative Craniology of the Ceratopsia. In: American Journal of Science 293, pp 200-234.
- ↑ Dodson, P. (1996). The Horned Dinosaurs. Princeton University Press, Pinceton, New Jersey, p244
- ↑ Ostrom, J. H., and P. Wellnhofer. 1986. The Munich specimen of Triceratops with a revision of the genus. Zitteliana 14: 111 - 158.
- ↑ Forster CA (1996): Species resolution in Triceratops: cladistic and morphometric approaches. J.Vert.Paleont. 16(2): 259-270
- ↑ Erickson, B.R. 1966. Mounted skeleton of Triceratops prorsus in the Science Museum. Scientific Publications of the Science Museum 1:1-16.
- ↑ Lehman T.M. 1987. Late Maastrichtian paleoenvironments and dinosaur biogeography in the Western interior of North America. Paleogeography, Paleoacclimatology and Paleoecology. 60: 189-217
- ↑ Dodson, P. (1996). The Horned Dinosaurs. Princeton University Press, Princeton, New Jersey, p79
- ↑ 18.0 18.1 18.2 18.3 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.
- ↑ Ostrom, J.H. 1966. Functional morphology and evolution of the ceratopsian dinosaurs. Evolution 20:290-308.
- ↑ Carpenter, K. 1998. Evidence of predatory behavior by carnivorous dinosaurs. Gaia 15: 135-144.
- ↑ Anton, in prep.; http://dml.cmnh.org/2000Nov/msg00543.html
- ↑ Farke, Andrew A. Horn Use in Triceratops (Dinosauria: Ceratopsidae): Testing Behavioral Hypotheses Using Scale Models. Palaeo-electronica, April 2004
- ↑ Tanke DH, and Farke AA. 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.
- ↑ Goodwin MB, Clemens WA, Horner JR, Padian K: The smallest known Triceratops skull: new observations on Ceratopsid cranial anatomy and ontogeny, Journal of Vertebrate Paleontology, 2006, 26(1):103-112
- Dodson, P. (1996). The Horned Dinosaurs. Princeton University Press, Pinceton, New Jersey, pp. xiv-346