Ceratopsidae (sometimes spelled Ceratopidae) is a family of ceratopsian including Triceratops, Centrosaurus, and Styracosaurus. All Knowledge species were Quadrupedalism herbivores from the Upper Cretaceous. All but one species are known from western North America, which formed the island continent of Laramidia during most of the Late Cretaceous. Ceratopsids are characterized by beaks, rows of shearing Tooth in the back of the jaw, elaborate nasal horns, and a thin parietal-squamosal shelf that extends back and up into a frill. The group is divided into two subfamilies—Chasmosaurinae and Centrosaurinae. The chasmosaurines are generally characterized by long, triangular frills and well-developed brow horns. The centrosaurines 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 is one possible purpose – although the frills are comparatively fragile in many species – but it is more likely that, as in modern , they were 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 butted heads. Centrosaurines have frequently been found in massive bone beds with few other species present, suggesting that the animals lived in large herds.
Paleobiology
Behavior
Fossil deposits dominated by large numbers of ceratopsids from individual species suggest that these animals were at least somewhat social.
However, the exact nature of ceratopsid social behavior has historically been controversial.
In 1997, Lehman argued that the aggregations of many individuals preserved in bonebeds originated as local "infestations" and compared them to similar modern occurrences in crocodiles and tortoises.
Other authors, such as Scott D. Sampson, interpret these deposits as the remains of large "socially complex" herds.
Modern animals with mating signals as prominent as the horns and frills of ceratopsians tend to form these kinds of large, intricate associations.
Other researchers who support the idea of ceratopsid herding have speculated that these associations were seasonal.
Diet
Ceratopsids were adapted to processing high-
fiber plant material with their highly derived
dental batteries and advanced dentition.
They may have utilized fermentation to break down plant material with a gut
microflora.
Mallon et al. (2013) examined herbivore coexistence on the island continent of
Laramidia, during the Late Cretaceous. It was concluded that ceratopsids were generally restricted to feeding on vegetation at, or below, the height of 1 meter.
Physiology
Ceratopsians probably had the "low mass-specific metabolic rate" typical of large bodied animals.
Sexual dimorphism
According to Scott D. Sampson, if ceratopsids were to have sexual dimorphism modern ecological analogues suggest it would be in their mating signals like horns and frills.
No convincing evidence for sexual dimorphism in body size or mating signals is known in ceratopsids, although it was present in the more primitive ceratopsian
Protoceratops andrewsi, whose sexes were distinguishable based on frill and nasal prominence size.
This is consistent with other known
tetrapod groups where midsized animals tended to exhibit markedly more sexual dimorphism than larger ones.
However, if there were sexually dimorphic traits, they may have been soft tissue variations like colorations or
that would not have been preserved as fossils.
Evolution
Scott D. Sampson has compared the evolution of ceratopsids to that of some mammal groups: both were rapid from a geological perspective and precipitated the simultaneous evolution of large body size, derived feeding structures, and "varied hornlike organs."
The earliest ceratopsids, including members of both Centrosaurinae and Chasmosaurinae are known from the early
Campanian stage, though the fossil record for early ceratopsids is poor.
All but one of the named species of ceratopsid is known from Western North America, which formed the island continent of
Laramidia during the Late Cretaceous, separated from the island continent of Appalachia to the east by the Western Interior Seaway. The latitudinal range of ceratopsians across Laramidia extends from Alaska to Mexico. The only named ceratopsid outside of Laramidia is
Sinoceratops, a centrosaurine from the late Campanian of China.
An indeterminate tooth of a ceratopsid is known from Mississippi dating to the late Maastrichtian, a few million years prior to the close of the Cretaceous, indicating that ceratopsids dispersed into eastern North America corresponding to the closure of the Western Interior Seaway at the end of the Cretaceous.
Paleoecology
The chief predators of ceratopsids were
tyrannosaurids.
Ca ratios in tyrannosaurids indicate that ceratopsids were among their most preferred prey.
There is evidence for an aggressive interaction between a Triceratops and a Tyrannosaurus in the form of partially healed tyrannosaur tooth marks on a Triceratops brow horn and squamosal (a bone of the neck frill); the bitten horn is also broken, with new bone growth after the break. It is not known what the exact nature of the interaction was, though: either animal could have been the aggressor.[Dodson, Peter, The Horned Dinosaurs, Princeton Press. p.19]
Classification
The
clade Ceratopsidae was in 1998 defined by
Paul Sereno as the group including the last common ancestor of
Pachyrhinosaurus and
Triceratops; and all its descendants.
In 2004,
Peter Dodson defined it to include
Triceratops,
Centrosaurus, and all descendants of their most recent common ancestor.
Ceratopsidae was given an official definition in the
PhyloCode by Daniel Madzia and colleagues in 2021 as "the smallest clade containing
Centrosaurus apertus,
Ceratops montanus,
Chasmosaurus belli, and
Triceratops horridus".
This definition ensures that the type species of Ceratopsidae,
Ceratops montanus, is included in the clade's definition.
See also
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Timeline of ceratopsian research
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Dodson, P. (1996). The Horned Dinosaurs. Princeton University Press, Princeton, New Jersey, pp. xiv-346
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Dodson, P., & Currie, P. J. (1990). "Neoceratopsia." 593–618 in Weishampel, D. B., Dodson, P., & Osmólska, H. (eds.), 1990: The Dinosauria. University of California Press, Berkeley, Los Angeles, Oxford, 1990 xvi-733.
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Sampson, S. D., 2001, Speculations on the socioecology of Ceratopsid dinosaurs (Ornithischia: Neoceratopsia): In: Mesozoic Vertebrate Life, edited by Tanke, D. H., and Carpenter, K., Indiana University Press, pp. 263–276.
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