Triceratops

Triceratops is a ceratopsid dinosaur genus which lived during the Late Cretaceous, about 68 million years ago, in the North American continent. It is one of the last dinosaur genera, which extincted in the Cretaceous-Paleogene mass extinction about 66 million years ago. The name Triceratops means ”three horned face”, and it is the most well-known ceratopsid, and also one of the most popular dinosaurs. The genus was described by Othniel Charles Mars in 1889[1]. However, only two brow horns were found in 1887, and first they were thought to belong to a huge, extinct bison species[2].

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Known occurrences of Triceratops fossils.

Valid species

Actually there was seventeen Triceratops species named and described previously, but now only two of them, T. horridus and T. prorsus are considered to be valid. Triceratops horridus is the type species of the genus. The two species are stratigraphically separated within the Hell Creek Formation, which means that they did not coexist at the same time[3]. Triceratops horridus skulls can be differentiated from T. prorsus on the basis of its shallower snout[4].

Description and anatomy

Triceratops had a large, bony frill at the caudal part of its skull, and also beared three horns – two longer at the level of the eyes (approximately 1 meters long), and one shorter in the top of the nasal part of the skull. Its length reached about 7.9 to 9 meters, and their height 2.9 to 3 meters, and weighed about between 6.1 and 12 tons[5]. This dinosaur had one of the largest skulls among all land animals; the largest Triceratops skull found was about 2.5 meters long[6], and it probably reached near the one-third of its total body length[7]. Triceratops possessed a large beak at the anterior part of the skull, in anteriorly to the teeth. The premaxilla had no teeth, but there was thirty-six to forty tooth positions in the maxilla. In each of these positions, three to five teeth were vertically settled. As tooth replacement was continous, only one tooth per position was used at a time. Triceratops was a quadrupedal dinosaur with strong limbs and a massively built body. It possessed three hooves on each hands of its forelimbs, and four on each feet of the hindlimbs. Earlier it was believed that the forelimbs needed to have a sprawling posture at a certain angle from the chest of the animal, in order to bear more effectively the mass of the head[8]. However, new results based on ichnological evidence from ceratopsids and recent physical and digital skeletal reconstructions suggest that these dinosaurs held their forelegs in a more upright stance normally (elbows flexed behind, and a bit bowed out), similarly to the modern rinoceros[9][10][11][12].


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Triceratops. By Creator: Dmitry Bogdanov - dmitrchel@mail.ru, CC BY 3.0, https://commons.wikimedia.org/w/index.php?curid=4522850

Paleobiology

Earlier the frill and the horns on the skull of the Triceratops were considered as defensive features against predators, but recent theories suggest that they were primarily used in courtship, helping the individuals to recognize conspecifics, and in dominance display. For a long time this dinosaur was known only from fossils of solitarily found specimens[13]. New results suggest that Triceratops lived in groups consisting of 5 – 10 specimens[14]. As Triceratops fossils are quite abundant, we can assume that it was amongst the most common herbivores in the Late Cretaceous North America. Triceratops was a herbivorous dinosaur, which probably grazed the low growing plants. It is likely that Triceratops was among the preys of Tyrannosaurus, as severel Triceratops bones with Tyrannosaurus tooth-scores were found. However, some of them showed signs of healing which might mean that in certain cases Triceratops survived the attack of Tyrannosaurus[15].


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Triceratops skeleton. By Source: Allie_CaulfieldDerivative: User:MathKnight - File:LA-Triceratops mount-1.jpg (by Allie_Caulfield ), CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=38858643

Scientific references

[1] Marsh, O.C. (1889): Notice of new American Dinosauria. American Journal of Science. 37 (220): 331–336. doi:10.2475/ajs.s3-37.220.331.

[2] Marsh, O.C. (1887): Notice of new fossil mammals. American Journal of Science. 34 (202): 323–331. doi:10.2475/ajs.s3-34.202.323.

[3] Scannella, J. B.; Fowler, D. W. (2009): Anagenesis in Triceratops: evidence from a newly resolved stratigraphic framework for the Hell Creek Formation. 9th North American Paleontological Convention Abstracts. Cincinnati Museum Center Scientific Contributions 3. pp. 148–149.

[4] Paul, G. S. (2010): The Princeton Field Guide to Dinosaurs. Princeton University Press. pp. 265–267. ISBN 978-0-691-13720-9.

[5] Alexander, R.M. (1985): Mechanics of posture and gait of some large dinosaurs. Zoological Journal of the Linnean Society. 83: 1–25. doi:10.1111/j.1096-3642.1985.tb00871.x.

[6] Scannella, J.; Horner, J.R. (2010): Torosaurus Marsh, 1891, is Triceratops Marsh, 1889 (Ceratopsidae: Chasmosaurinae): synonymy through ontogeny. Journal of Vertebrate Paleontology. 30 (4): 1157–1168. doi:10.1080/02724634.2010.483632.

[7] Lambert, D. (1993): The Ultimate Dinosaur Book. Dorling Kindersley, New York. pp. 152–167. ISBN 978-1-56458-304-8.

[8] Dodson, P. (1996). The Horned Dinosaurs. Princeton, New Jersey: Princeton University Press. ISBN 978-0-691-02882-8.

[9] Fujiwara, Shin-Ichi (2009): A reevaluation of the manus structure in Triceratops (Ceratopsia: Ceratopsidae)". Journal of Vertebrate Paleontology. 29 (4): 1136–1147. doi:10.1671/039.029.0406.

[10] Christiansen, P.; Paul, G.S. (2001): Limb bone scaling, limb proportions, and bone strength in neoceratopsian dinosaurs. Gaia. 16: 13–29.

[11] Thompson, S.; Holmes, R. (2007): Forelimb stance and step cycle in Chasmosaurus irvinensis (Dinosauria: Neoceratopsia)". Palaeontologia Electronica. 10 (1): 17 p.

[12] Rega, E.; Holmes, R.; Tirabasso, A. (2010): Habitual locomotor behavior inferred from manual pathology in two Late Cretaceous chasmosaurine ceratopsid dinosaurs, Chasmosaurus irvinensis (CMN 41357) and Chasmosaurus belli (ROM 843). In Ryan, Michael J.; Chinnery-Allgeier, Brenda J.; Eberth, David A. (eds.). New Perspectives on Horned Dinosaurs: The Royal Tyrrell Museum Ceratopsian Symposium. Bloomington and Indianapolis: Indiana University Press. pp. 340–354. ISBN 978-0-253-35358-0.

[13] Mathews, Joshua C.; Brusatte, Stephen L.; Williams, Scott A.; Henderson, Michael D. (2009): The first Triceratops bonebed and its implications for gregarious behavior. Journal of Vertebrate Paleontology. 29 (1): 286–290. doi:10.1080/02724634.2009.10010382.

[14] Barrera, Nathanial A. (2020): More than old bones: New study sheds light on Triceratops behavior and living habits. The Dickinson Press. Retrieved March 31, 2020.

[15] Happ, J. (2008): An analysis of predator-prey behavior in a head-to-head encounter between Tyrannosaurus rex and Triceratops. In Larson, P.; Carpenter, K. (eds.). Tyrannosaurus rex, the Tyrant King (Life of the Past). Bloomington: Indiana University Press. pp. 355–368. ISBN 978-0-253-35087-9.