Ceratopsidae

Ceratopsids Temporal range: Late Cretaceous, 84–66 Ma PreЄ Є O S D C P T J K Pg N
Triceratops prorsus skeleton, Natural History Museum of Los Angeles County.
Centrosaurus nasicornus skeleton, Palaeontological Museum Munich
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Reptilia
Clade:	Dinosauria
Order:	†Ornithischia
Superfamily:	†Ceratopsoidea
Family:	†Ceratopsidae Marsh, 1890
Subgroups
†Centrosaurinae †Chasmosaurinae
Synonyms
Agathaumidae Cope, 1891 Pachyrhinosauridae Sternberg, 1950

Agathaumidae Cope, 1891
Pachyrhinosauridae Sternberg, 1950

Ceratopsidae (sometimes spelled Ceratopidae) is a speciose group of marginocephalian dinosaurs including Triceratops and Styracosaurus. All known species were quadrupedal herbivores from the Upper Cretaceous, mainly of Western North America (though Sinoceratops is known from Asia) and are characterized by beaks, rows of shearing teeth in the back of the jaw, and elaborate horns and frills. The group is divided into two subfamilies. The Ceratopsinae or Chasmosaurinae are generally characterized by long, triangular frills and well-developed brow horns. The Centrosaurinae had well-developed nasal horns or nasal bosses, shorter and more rectangular frills, and elaborate spines on the back of the frill.

These horns and frills show remarkable variation and are the principal means by which the various species have been recognized. Their purpose is not entirely clear. Defense against predators is one possible purpose – although the frills are comparatively fragile in many species – but it is more likely that, as in modern ungulates, they may have been secondary sexual characteristics used in displays or for intraspecific combat. The massive bosses on the skulls of Pachyrhinosaurus and Achelousaurus resemble those formed by the base of the horns in modern musk oxen, suggesting that they may have butted heads. Centrosaurines have frequently been found in massive bone beds with few other species present, suggesting that the animals might have lived in large herds.