Almost all leptoceratopsids are North American, aside from Udanoceratops, which may represent a separate dispersal event, back into Asia. Ceratopsids and their immediate ancestors, such as Zuniceratops, were unknown outside of western North America, and were presumed endemic to that continent. The traditional view that ceratopsoids originated in North America was called into question by the 2009 discovery of better specimens of the dubious Asian form Turanoceratops, which confirmed it as a ceratopsid. It is unknown whether this indicates ceratopsids actually originated in Asia, or if the Turanoceratops immigrated from North America. Possible ceratopsians from the Southern Hemisphere include the Australian Serendipaceratops, known from an ulna, and Notoceratops from Argentina is known from a single toothless jaw (which has been lost). Craspedodon from the Late Cretaceous (Santonian) of Belgium may also be a ceratopsian, specifically a neoceratopsian closer to ceratopsoidea than protoceratopsidae. Possible leptoceratopsid remains have also been described from the early Campanian of Sweden. Ecological role Psittacosaurus and Protoceratops are the most common dinosaurs in the different Mongolian sediments where they are found. Triceratops fossils are far and away the most common dinosaur remains found in the latest Cretaceous rocks in the western United States, making up as much as 5/6ths of the large dinosaur fauna in some areas. These facts indicate that some ceratopsians were the dominant herbivores in their environments. Some species of ceratopsians, especially Centrosaurus and its relatives, appear to have been gregarious, living in herds. This is suggested by bonebed finds with the remains of many individuals of different ages. Like modern migratory herds, they would have had a significant effect on their environment, as well as serving as a major food source for predators. References External links Introduction to the Ceratopsians, University of California Museum of Paleontology Marginocephalia at Palaeos.com (technical) Marginocephalians Late Jurassic first appearances Maastrichtian extinctions Taxa named by Othniel Charles Marsh