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 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. 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. Since the Triceratops wounds healed, it is most likely that the Triceratops survived the encounter and managed to overcome the Tyrannosaurus. Paleontologist Peter Dodson estimates that in a battle against a bull Tyrannosaurus, the Triceratops had the upper hand and would successfully defend itself by inflicting fatal wounds to the Tyrannosaurus using its sharp horns. 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, it was by Peter Dodson defined to include Triceratops, Centrosaurus, and all descendants of their most recent common ancestor. See also Timeline of ceratopsian research References Dodson, P. (1996). The Horned Dinosaurs. Princeton University Press, Princeton, New Jersey, pp. xiv-346 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. 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. Footnotes External links Campanian first appearances Maastrichtian extinctions Taxa named by Othniel Charles Marsh Prehistoric dinosaur families