Triceratops

*Triceratops horridus*

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***Triceratops*** (pronounced /traɪˈsɛrətɒps/) is an extinct genus of herbivorous ceratopsid dinosaur which lived during the late Maastrichtian stage of the Late Cretaceous Period, around 68 to 66 million years ago (mya) in what is now North America. It was one of the last dinosaur genera to appear before the great Cretaceous–Tertiary extinction event. Bearing a large bony frill and three horns on its large four-legged body, and conjuring similarities with the modern rhinoceros, *Triceratops* is one of the most recognizable of all dinosaurs. Although it shared the landscape with and was preyed upon by the fearsome *Tyrannosaurus*, it is unclear whether the two battled the way they are commonly depicted in movies, children's dinosaur books and many cartoons. The fossil can be found in the United States.

A complete *Triceratops* skeleton has yet to be found; however, the animal is well-known from numerous partial remains collected since the introduction of the genus in 1887. The function of their frills and three distinctive facial horns has long inspired debate. Although traditionally viewed as defensive weapons against predators, the latest theories claim that it is more probable that these features were used in courtship and dominance displays, much like the antlers and horns of modern reindeer, mountain goats, or rhinoceros beetles.

*Triceratops* is the best-known of the ceratopsids, though the genus's exact placement within the group has been a point of contention amongst paleontologists. Two species, *T. horridus* and *T. prorsus*, are considered valid, although many other species have been named.

## Description

Individual *Triceratops* are estimated to have reached about 7.9 to 9.0 m (26.0–29.5 ft) in length, 2.9 to 3.0 m (9.5–9.8 ft) in height, and 6.1–12.0 tonnes (13,000-26,000 lb) in weight. The most distinctive feature is their large skull, among the largest of all land animals. It could grow to be over 2 m (7 ft) in length, and could reach almost a third of the length of the entire animal. It bore a single horn on the snout, above the nostrils, and a pair of horns approximately 1 m (3 ft) long, with one above each eye. To the rear of the skull was a relatively short, bony frill. Most other frilled dinosaurs had large fenestrae in their frills, while the frills of *Triceratops* were noticeably solid.

*Triceratops* species possessed a sturdy build, with strong limbs and short five-hoofed hands and four-hoofed feet. Although certainly quadrupedal, the posture of these dinosaurs 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 the form of trackways from horned dinosaurs, and recent reconstructions of skeletons (both physical and digital) 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 conclusion does not preclude a sprawling gait for confrontations or feeding.

## Classification

*Triceratops* is the best known genus 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 combination of short, solid frills (similar to that of Centrosaurinae), and the long brow horns (more akin to Ceratopsinae, also known as Chasmosaurinae). In the first overview of horned dinosaurs, R.S. Lull hypothesized two lineages, one of *Monoclonius* and *Centrosaurus* leading to *Triceratops*, the other with *Ceratops* and *Torosaurus*, making *Triceratops* a centrosaurine as the group is understood today. Later revisions supported this view, formally describing the first, short-frilled group as Centrosaurinae (including *Triceratops*), and the second, long-frilled group as Chasmosaurinae.

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, making *Triceratops* a ceratopsine (chasmosaurine of his usage) genus. However, he was largely ignored with John Ostrom, and later David Norman, both placing *Triceratops* within Centrosaurinae.

Subsequent discoveries and analyses upheld Sternberg's view on the position of *Triceratops*, with Lehman defining both subfamilies in 1990 and diagnosing *Triceratops* as ceratopsine (chasmosaurine of his usage) on the basis of several morphological features. In fact, it fits well into the ceratopsine subfamily, apart from its one feature of a shortened frill. Further research by Peter Dodson, including a 1990 cladistic analysis and a 1993 study using RFTRA (resistant-fit theta-rho analysis), a morphometric technique which systematically measures similarities in skull shape, reinforces *Triceratops'* placement in the ceratopsine subfamily.

### Use in phylogenetics

In phylogenetic taxonomy, the genus has been used as a reference point in the definition of Dinosauria; Dinosaurs have been designated as all descendants of the most recent common ancestor of *Triceratops* and Neornithes (i.e. modern birds). Furthermore, the bird-hipped dinosaurs, Ornithischia, have been designated as all dinosaurs with a more recent common ancestor to *Triceratops* than modern birds.

### 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 passed before additional findings came to light. However, recent years have been fruitful for the discovery of several dinosaurs related to ancestors of *Triceratops*. *Zuniceratops*, the earliest known ceratopsian with brow horns, was described in the late 1990s, and *Yinlong*, the first known Jurassic ceratopsian, in 2005.

These new finds have been vital in illustrating the origins of horned dinosaurs in general, suggesting an Asian origin in the Jurassic, and the appearance of truly horned ceratopsians by the beginning of the late Cretaceous in North America. As *Triceratops* is increasingly shown to be a member of the long-frilled Ceratopsinae subfamily, a likely ancestor may have resembled *Chasmosaurus*, which thrived some 5 million years earlier.

## History

### Etymology

The term *Triceratops*, which literally means "three-horned face", is derived from the Greek *tri/τρι-* meaning "three", *ceras/κέρας* meaning "horn", and *-ops/ωψ* meaning "face".

### Discoveries and species

The first named specimen now attributed to *Triceratops* is a pair of brow horns attached to a skull roof, found near Denver, Colorado in the spring of 1887. This specimen was sent to Othniel Charles Marsh, who believed that the formation from which it came dated from the Pliocene, and that the bones belonged to a particularly large and unusual bison, which he named *Bison alticornis*. He realized that there were horned dinosaurs by the next year, which saw his publication of the genus *Ceratops* from fragmentary remains, but he still believed *B. alticornis* to be a Pliocene mammal. It took a third and much more complete skull to change his mind. The specimen, collected in 1888 by John Bell Hatcher from the Lance Formation of Wyoming, was initially described as another species of *Ceratops*. After reflection, however, Marsh changed his mind and gave it the generic name *Triceratops*, accepting his *Bison alticornis* as another species of *Ceratops* (it would later be added to *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 the American states of Montana and South Dakota (in addition to Colorado and Wyoming), and in the Canadian provinces of Saskatchewan and Alberta.

#### Number of species

Within 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 the Latin *horridus*; "rough, rugose", suggesting the roughened texture of those bones belonging to the type specimen, later identified as an aged individual). 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 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*; the other of *T. elatus* and *T. calicornis*. Two species (*T. serratus* and *T. flabellatus*) stood apart from these groups. By 1933, and his revision of the landmark 1907 Hatcher-Marsh-Lull monograph of all known ceratopsians, 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. C. M. 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.

With time, 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 in which they proposed that there was only one species, *Triceratops horridus*. Part of their rationale was that generally there are only three to four species of any large animal in a region (modern examples being the elephant, giraffe, rhinoceros, and hippopotamus 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. hatcheri* (now *Nedoceratops*) differed enough to warrant a separate genus. She found that *T. horridus* and several other species belonged together, and *T. prorsus* and *T. brevicornus* stood alone, and since there were many more specimens in the first group, she suggested that this meant the two groups were two species. It is still possible to interpret this reasoning as describing a single species with sexual dimorphism.

#### Valid species

* *T. horridus* (Marsh, 1889) (originally *Ceratops*) (type species)
* *T. prorsus* (Marsh, 1890)

#### Doubtful species

The following species are considered *nomina dubia* ("dubious names"), and are based on remains that are too poor or incomplete to be distinguished from pre-existing *Triceratops* species.

* *T. albertensis* (C. M. 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. brevicornus* (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) (=*Diceratus 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 sylvestris*)

## Paleobiology

Although *Triceratops* are commonly portrayed as herding animals, there is currently no solid evidence that they 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, these remains are very common; for example, Bruce Erickson, a paleontologist of the Science Museum of Minnesota, has reported having seen 200 specimens of *T. prorsus* in the Hell Creek Formation of Montana. 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 (late Cretaceous, 68 to 65 mya) Period of western North America, it is regarded as among the dominant herbivores of the time, if not the most dominant herbivore. In 1986, Robert Bakker estimated it as making up 5/6ths of the large dinosaur fauna at the end of the Cretaceous. Unlike most animals, skull fossils are far more common than postcranial bones for *Triceratops*, suggesting that the skull had an unusually high preservation potential.

*Triceratops* was one of the last ceratopsian genera to appear before the Cretaceous-Tertiary extinction event. The related *Diceratus* and *Torosaurus*, and the more distantly related diminutive *Leptoceratops*, were also present, though their remains have been rarely encountered.

### Dentition and diet

*Triceratops* were herbivorous, and because of their low head, their primary food was probably low growth, although they may have been able to knock down taller plants with their horns, beak, and bulk. The jaws were tipped with a deep, narrow beak, believed to have been better at grasping and plucking than biting.

*Triceratops* teeth were arranged in groups called batteries, of 36 to 40 tooth columns, in each side of each jaw with 3 to 5 stacked teeth per column, depending on the size of the animal. This gives a range 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 by shearing in a vertical to near-vertical orientation. The great size and numerous teeth of *Triceratops* suggests that they ate large volumes of fibrous plant material, with some suggesting palms and cyads  and others suggesting ferns, which then grew in prairies.

### 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 frills may have served as anchor points for the jaw muscles to aid chewing by allowing increased size and thus power for the muscles. This has been put forward by other authors over the years, but later studies do not find evidence of large muscle attachments on the frill bones.

*Triceratops* were long thought to have possibly used their horns and frills in combat with predators such as *Tyrannosaurus*, the idea being discussed first by C. H. Sternberg in 1917 and 70 years later by Robert Bakker. There is evidence that *Tyrannosaurus* did have aggressive head-on encounters with *Triceratops*, based on partially-healed tyrannosaur tooth marks on a *Triceratops* brow horn and squamosal; the bitten horn is also broken, with new bone growth after the break. Which animal was the aggressor is not known. *Tyrannosaurus* is also known to have fed on *Triceratops*. Evidence for this includes a heavily tooth-scored *Triceratops* ilium and sacrum.

In 2005, a BBC documentary, *The Truth About Killer Dinosaurs*, tested how *Triceratops* might have defended themselves 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 themselves in this way—instead they probably stood their ground when attacked by large predators, using their horns for goring if the predator came close enough.

In addition 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 disagreement about whether they actually did so. Additionally, although pitting, holes, lesions, and other damage on *Triceratops* skulls (and the skulls of other ceratopsids) are often attributed to horn damage in combat, a recent study finds no evidence for horn thrust injuries causing these forms of damage (for example, there is no evidence of infection or healing). Instead, non-pathological bone resorption, or unknown bone diseases, are suggested as causes. However, a newer study compared incidence rates of skull lesions in *Triceratops* and *Centrosaurus* and showed that these were consistent with *Triceratops* using its horns in combat and the frill being adapted as a protective structure, while lower pathology rates in *Centrosaurus* may indicate visual rather than physical use of cranial ornamentation, or a form of combat focused on the body rather than the head.

The large frill also may have helped to increase body area to regulate body temperature. A similar theory has been proposed regarding the plates of *Stegosaurus*, although this use alone would not account for the bizarre and extravagant variation seen in different members of the Ceratopsidae. This observation is highly suggestive of what is now believed to be the primary function, display.

The theory of their use in sexual display was first proposed by Davitashvili in 1961 and has gained increasing acceptance since. Evidence that visual display was important, either in courtship or in other social behavior, 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 behavior. A recent study of the smallest *Triceratops* skull, ascertained to be a juvenile, shows the frill and horns developed at a very early age, predating sexual development and thus probably important for visual communication and species recognition in general. The large eyes and shortened features, a hallmark of "cute" baby mammals, also suggest that the parent *Triceratops* may have cared for its young.

## Cultural Influence

The distinctive appearance of *Triceratops* has led to them being frequently depicted in films, computer games and documentaries. They appear in the film *Jurassic Park*, where one is portrayed as sick and is being treated by humans. More active *Triceratops* are also seen in the film's two sequels. They have also been featured in three major dinosaur documentaries: *Walking with Dinosaurs*, *The Truth About Killer Dinosaurs* and *Prehistoric Park*.

They are famously known as "three-horns" (and are so named in *The Land Before Time* animated film and its numerous sequels) due to the three prominent horns on their head and nose, which have become almost synonymous with the dinosaurs. The shorthand "Trike" is another common informal name, and is also the name of the *Triceratops* character in the children's book series and television cartoon series *Harry and His Bucket Full of Dinosaurs*. The character "Baby Bop" from *Barney & Friends* is another example of a *Triceratops* in popular media.

A recurring theme, especially in children's dinosaur books, is a climactic showdown or battle between *Triceratops* and *T. rex*. As such these two dinosaurs are often depicted and thought of as natural enemies. A memorable but anachronistic battle with *Ceratosaurus* substituting for *T. rex* is featured in the 1966 movie *One Million Years B.C.*.

*Triceratops* appears in video games either derived directly from the *Jurassic Park* series or similarly themed, namely the 1997 PC games *Jurassic Park: Chaos Island* and *Turok: Dinosaur Hunter*, and the 2000 PC and PlayStation game *Dino Crisis 2*. *Triceratops* also features in the *Zoo Tycoon* franchise. As well, it is a popular creature used in games designed by Rareware, including *Diddy Kong Racing* and *Starfox Adventures*. *Triceratops* (the species are not identified) is also the official state fossil of South Dakota, and the official state dinosaur of Wyoming.

There is also a Japanese rock band called *Toraiseratoppusu*, which translates into English as *Triceratops*.

## Trivia:

* There is a theory that wasn't confirmed that Triceratops are actually teenagers Torosaurus.

## JPInstitute.com Description

One of the top three on everyone's favorite dinosaur list, Triceratops is a very common dinosaur which lived at the very end of the Age of Dinosaurs. It had a huge frilled head with horns over each eye that could reach over 3 feet long. Triceratops had a third, smaller horn on its nose. These would be fearsome weapons against a predator.

Triceratops is one of the most common dinosaur fossils found. More than 50 skulls have been found. Within the genus, at least 7 species have been identified. The ceratopsian family is one of the most successful and varied of the Late Cretaceous. Triceratops is the largest member of this family, reaching the size of a school bus.

Triceratops was a herd animal; it is believed that large groups roamed North America. Their large, horny beaks and long rows of teeth were well designed for chewing the tough, low growing plants of the Late Cretaceous. It was likely the main predator of these animals was T. rex. A number of skeletons show bite and chew marks that match the teeth of T. rex. Horns and frills seemed to vary among individuals within the species. Some frills were very broad, others narrow. The nasal horn shows the most variance among individual specimens, no two being the same. The material that covered its horns in life would have added significantly to the length of the fossilized bone.

## Dinosaur Field Guide Description

Triceratops ("three-horned face") may hold the record for holding records! It has the largest skull (tied with Torosaurus at 10 feet/3 m) and longest hip bone (4 feet/1.2 m) of any dinosaur, the strongest jaw of any land dwelling herbivore (or plant-eater that's ever lived, and the largest teeth of any herbivorous dinosaur. It was also the second most famous dinosaur, after Tyrannosaurus, for over a century; the first big dinosaur mounted at the Smithsonian Institution; and the first fully restored horned dinosaur (family Ceratopsidae). With its parrot-like beak, self-sharpening and ever-replacing teeth with muscles, 3-foot (I m) horns, and body more powerful than a rhino, Triceratops was the only dinosaur that could (and sometimes did) outfight a T. rex!

### Fun Facts

One scientist assumed the first Triceratops specimen belonged to a bison.

### Trivia

In 1999, Triceratops became the world's first fully "digital dinosaur." The Smithsonian's complete mounted skeleton- as well as each individual bone--was scanned into a computer and made available on their Web site, where you can move its individual bones.

## Appearance in Jurassic Park and other media

### *Jurassic Park*

*Triceratops* appeared in all five Jurassic Park movies. However, it only played an important role in the first film, where an individual is sick and has collapsed, leading the characters to try to figure out what's wrong with it. Unlike the originals, the adult clones have triangular epoccipitals around their frills but in real life, the triangular epoccipitals can only be found on young and juveniles. It also shows that it has jugal cheek horns instead of one cheek horn on each side of the head.

### *The Land Before Time*

The most notable *Triceratops* in the series are Cera, one of the main characters, Topps, Cera's father, Tria, her stepmother, and Tricia, her half-sister. Other *Triceratops* throughout the franchise include Cera's mother, full siblings, and her niece and nephew, Dinah and Dana. There are many background characters who are *Triceratops*.

## Links

* https://web.archive.org/web/20040806054211fw\_/http://www.jpinstitute.com/dinopedia/dinocards/dc\_trice.html
* https://web.archive.org/web/20080517084524/http://kids.yahoo.com/dinosaurs/48--Triceratops

## References

1. ↑ Lehman T.M., 1987 *Late Maastrichtian paleoenvironments and dinosaur biogeography in the Western Interior of North America*, from the Journal of *Paleogeography, Paleoacclimatology and Paleoecology*, vol. 60, pp. 290.
2. ↑ Fowler, D. W., and Sullivan, R. M. (2006). A ceratopsid pelvis with toothmarks from the Upper Cretaceous Kirtland Formation, New Mexico: evidence of late Campanian tyrannosaurid feeding behavior. *New Mexico Museum of Natural History and Science Bulletin* **35**:127–130.
3. ↑ 3.0 3.1 Erickson, GM, and Olson, KH, in 1996. "Bite marks attributable to *Tyrannosaurus rex*: preliminary description and implications", from the Journal of Vertebrate Paleontology, vol. 16, issue 1, pages 175–178.
4. ↑ 4.0 4.1 *The Ultimate Dinosaur Book*, 1993, by Lambert, D.; pp. 152–167. Published by Dorling Kindersley, New York, ISBN 1-56458-304-X
5. ↑ 5.0 5.1 5.2 5.3 5.4 5.5 5.6 *The Horned Dinosaurs*, 1996, by Dodson, P. Published by the Princeton University Press, Princeton, New Jersey, ISBN 0-691-02882-6
6. ↑ DinoDictionary.com :: T Dinosaurs Page 2
7. ↑ Triceratops in The Natural History Museum's Dino Directory
8. ↑ Alexander, R.M. (1985). "Mechanics of posture and gait of some large dinosaurs." *Zoological Journal of the Linnean Society*, 83, 1–25.
9. ↑ 9.0 9.1 9.2 9.3 9.4 9.5 9.6 9.7 9.8 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.
10. ↑ Christiansen, P., and Paul, G.S. (2001). Limb bone scaling, limb proportions, and bone strength in neoceratopsian dinosaurs. *Gaia* **16**:13–29.
11. ↑ 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.
12. ↑ 12.0 12.1 12.2 Hatcher, J. B., Marsh, O. C. and Lull, R. S. (1907) *The Ceratopsia*. Government Printing Office, Washington, D.C. ISBN 0405127138.
13. ↑ Lambe, L.M. (1915). On *Eoceratops canadensis*, gen. nov., with remarks on other genera of Cretaceous horned dinosaurs. *Canada Department of Mines Geological Survey Museum Bulletin* **12**:1–49.
14. ↑ 14.0 14.1 14.2 Lull, R. S. (1933) A revision of the Ceratopsia or horned dinosaurs. *Memoirs of the Peabody Museum of Natural History* **3**(3):1–175.
15. ↑ 15.0 15.1 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.
16. ↑ Ostrom, J. H. (1966). Functional morphology and evolution of the ceratopsian dinosaurs. *Evolution* **20**:220–227.
17. ↑ Norman, David; *The Illustrated Encyclopaedia of Dinosaurs*. Published 1985, by Salamander Books, in London. ISBN 0-517-468905
18. ↑ 18.0 18.1 18.2 Lehman, T. M. (1990). The ceratopsian subfamily Chasmosaurinae: sexual dimorphism and systematics. in: Carpenter, K., and Currie, P. J. (eds.). *Dinosaur Systematics: Perspectives and Approaches*, Cambridge University Press, Cambridge, pp. 211–229. ISBN 0-521-36672-0.
19. ↑ Dodson, P., and Currie, P. J. (1990). Neoceratopsia. 593–618. in Weishampel, D. B., Dodson, P., & Osmólska, H. (eds.). *The Dinosauria* University of California Press:Berkeley, pp. 593–618. ISBN 0-520-06727-4.
20. ↑ Dodson, P. (1993). Comparative Craniology of the Ceratopsia. In: *American Journal of Science* **293**, pp. 200–234.
21. ↑ Gauthier, J. A. (1986). Saurischian monophyly and the origin of birds. The Origin of Birds and the Evolution of Flight, K. Padian (ed.), *Memoirs of the California Academy of Sciences* **8**:1–55.
22. ↑ Sereno, P. C. (1998). A rationale for phylogenetic definitions, with application to the higher-level taxonomy of Dinosauria. *Neues Jahrbuch für Geologie und Paläontologie, Abhandlungen* **210**(1):41–83.
23. ↑ Dodson, P. (1996). *The Horned Dinosaurs*. Princeton University Press:Princeton, New Jersey, p. 244. ISBN 0-691-02882-6.
24. ↑ Liddell & Scott, 1980; *Greek-English Lexicon, Abridged Edition*. Published by the Oxford University Press, Oxford, UK. ISBN 0-19-910207-4
25. ↑ 25.0 25.1 Carpenter, K. (2006). "*Bison*" *alticornis* and O.C. Marsh's early views on ceratopsians. In: Carpenter, K. (ed.). *Horns and Beaks: Ceratopsian and Ornithopod Dinosaurs* Indiana University Press:Bloomington and Indianapolis, pp. 349–364. ISBN 0-253-34817-X.
26. ↑ Marsh, O.C. (1887). Notice of new fossil mammals. *American Journal of Science* **34**:323–331.
27. ↑ Marsh, O.C. (1888). A new family of horned Dinosauria, from the Cretaceous. *American Journal of Science* **36**:477–478.
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59. ↑ State of South Dakota, *Signs and Symbols of South Dakota.....* [1].
60. ↑ State of Wyoming, *State of Wyoming - General Information*, [2].