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From Wikipedia, the free encyclopedia
Ceratopsia, meaning "horned faces", is an infraorder of quadrupedal herbivorous ornithischian dinosaurs. Ceratopsians ranged in size from 1 meter (3 ft) and 23 kilograms (50 lb) to over 9 meters (30 ft) and 5,400 kg (12,000 lb). The group first appeared during the late Jurassic in Asia and evolved from bipedal ancestral forms. These basal ceratopsians, such as Psittacosaurus and Yinlong, possessed prominent bumps and ridges over the nose and eyes which would later develop into the elaborate displays found in late Cretaceous forms. By the middle of the Cretaceous period had dispersed across what is now the Bering Strait into North America. Possible late Cretaceous forms have been found in southern Australia, Europe, and South America. As the group entered the late Cretaceous many forms, including ceratopsids like Centrosaurus and Triceratops, evolved large and elaborate head displays with large horns and frills. 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 became extinct, along with most other life forms, during the Cretaceous–Paleogene extinction event 65.5 million years ago.
Ceratopsian remains were first discovered in southwestern Wyoming in 1872 by Fielding Bradford Meek. Agathaumas was described that same year from these remains by Edward Drinker Cope, and was the first ceratopsian genus to be described. Ceratopsia was coined by Cope's rival, Othniel Charles Marsh, in 1890. Another early described genus was Ceratops, which lent its name to the group, although it and Agathaumas are considered a nomen dubium today. Triceratops is by far the best-known ceratopsian to the general public.
All ceratopsians possess a rostral bone, which is the basis for the parrot-like beak. Ceratopsians are a wide-ranging group, and several families exist. Basal forms include leptoceratopsids, psittacosaurids, and protoceratopsids. More derived forms include the late Cretaceous ceratopsids, which grew to enormous sizes. While herbivorous, many ceratopsians, especially basal forms, may have been omnivorous. Late Cretaceous bonebeds have been uncovered in Western North America that show ceratopsians as gregarious social animals.