 = Ceratopsia = 
 
 Ceratopsia or <unk> ( / <unk> / or / <unk> / ; Greek : " horned faces " ) is a group of herbivorous , <unk> dinosaurs that <unk> in what are now North America , Europe , and Asia , during the Cretaceous Period , although ancestral forms lived earlier , in the Jurassic . The earliest known ceratopsian , Yinlong <unk> , lived between 161 @.@ 2 and 155 @.@ 7 million years ago . The last ceratopsian species , Triceratops <unk> , became extinct during the Cretaceous – <unk> extinction event , 66 million years ago . 
 Early members of the ceratopsian group , such as Psittacosaurus , were small bipedal animals . Later members , including ceratopsids like Centrosaurus and Triceratops , became very large <unk> and developed elaborate facial horns and frills extending over the neck . While these frills might have served to protect the vulnerable neck from predators , they may also have been used for display , <unk> , the attachment of large neck and chewing muscles or some combination of the above . <unk> 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 ) . 
 Triceratops is by far the best @-@ known ceratopsian to the general public . It is traditional for ceratopsian genus names to end in " <unk> " , although this is not always the case . One of the first named genera was Ceratops itself , which lent its name to the group , although it is considered a nomen dubium today as its fossil remains have no distinguishing characteristics that are not also found in other ceratopsians . 
 
 = = Anatomy = = 
 
 <unk> are easily recognized by features of the skull . On the tip of a ceratopsian upper jaw is the rostral bone , an <unk> ( toothless ) ossification , unique to ceratopsians . Othniel Charles Marsh recognized and named this bone , which acts as a mirror image of the <unk> bone on the lower jaw . This ossification evolved to <unk> aid the <unk> of plant matter . Along with the <unk> bone , which forms the tip of the lower jaw in all ornithischians , the rostral forms a superficially parrot @-@ like beak . Also , the jugal bones below the eye are very tall and flare out sideways , making the skull appear somewhat triangular when viewed from above . This triangular appearance is <unk> in later ceratopsians by the <unk> extension of the parietal and <unk> bones of the skull roof , to form the neck frill . 
 The <unk> is a distinctive bones found lining the frills of ceratopsians . The name is a <unk> , as they are not associated with the <unk> bone . <unk> begin as separate bones that fuse during the animal 's growth to either the <unk> or parietal bones that make up the base of the frill . These bones were ornamental instead of functional , and may have helped differentiate species . <unk> probably were present in all known ceratopsids with the possible exception of Zuniceratops . They appear to have been broadly different between short @-@ frilled ceratopsids ( <unk> ) and long @-@ frilled ceratopsids ( <unk> ) , being elliptical with <unk> bases in the former group , and triangular with wide bases in the latter group . Within these broad definitions , different species would have somewhat different shapes and numbers . In <unk> especially , like Centrosaurus , <unk> , and <unk> , these bones become long and <unk> or hook @-@ like . A well @-@ known example is the coarse <unk> fringe of broad triangular <unk> on the frill of Triceratops . When regarding the ossification 's <unk> traits , it can be described as dermal . The term <unk> was coined by famous paleontologist Othniel Charles Marsh in 1889 . 
 
 = = History of study = = 
 
 The first ceratopsian remains known to science were discovered during the U.S. Geological and Geographical Survey of the Territories led by the American geologist <unk> <unk> . <unk> discovered during an 1855 expedition to Montana were first assigned to hadrosaurids and included within the genus Trachodon . It was not until the early 20th century that some of these were recognized as ceratopsian teeth . During another of <unk> 's expeditions in 1872 , Fielding Bradford <unk> found several giant bones protruding from a hillside in southwestern Wyoming . He alerted paleontologist Edward <unk> Cope , who led a dig to recover the partial skeleton . Cope recognized the remains as a dinosaur , but noted that even though the fossil lacked a skull , it was different from any type of dinosaur then known . He named the new species Agathaumas <unk> , meaning " marvellous forest @-@ dweller " . Soon after , Cope named two more dinosaurs that would eventually come to be recognized as ceratopsids : <unk> and Monoclonius . Monoclonius was notable for the number of <unk> remains found , including the first evidence of ceratopsid horns and frills . Several Monoclonius fossils were found by Cope , assisted by Charles <unk> Sternberg , in the summer of 1876 near the Judith River in <unk> County , Montana . Since the ceratopsians had not been recognised yet as a distinctive group , Cope was uncertain about much of the fossil material , not recognizing the nasal horn core , nor the brow horns , as part of a fossil horn . The frill bone was interpreted as a part of the <unk> . 
 In 1888 and 1889 , Othniel Charles Marsh described the first well preserved horned dinosaurs , Ceratops and Triceratops . In 1890 Marsh classified them together in the family Ceratopsidae and the order Ceratopsia . This prompted Cope to <unk> his own specimens and to realized that Triceratops , Monoclonius , and Agathaumas all represented a single group of similar dinosaurs , which he named <unk> in 1891 . Cope <unk> Monoclonius as a horned dinosaur , with a large nasal horn and two smaller horns over the eyes , and a large frill . 
 
 = = Classification = = 
 
 Ceratopsia was coined by Othniel Charles Marsh in 1890 to include dinosaurs possessing certain characteristic features , including horns , a rostral bone , teeth with two roots , fused neck vertebrae , and a forward @-@ oriented <unk> . Marsh considered the group distinct enough to warrant its own suborder within <unk> . The name is derived from the Greek <unk> / <unk> meaning ' horn ' and <unk> / <unk> meaning ' face ' . As early as the 1960s , it was noted that the name Ceratopsia is actually incorrect linguistically and that it should be <unk> . However , this spelling , while technically correct , has been used only rarely in the scientific literature , and the vast majority of paleontologists continue to use Ceratopsia . As the <unk> does not govern taxa above the level of superfamily , this is unlikely to change . 
 
 = = = Taxonomy = = = 
 
 Following Marsh , Ceratopsia has usually been classified as a suborder within the order <unk> . While ranked taxonomy has largely fallen out of favor among dinosaur paleontologists , some researchers have continued to employ such a classification , though sources have differed on what its rank should be . Most who still employ the use of ranks have retained its traditional ranking of suborder , though some have reduced to the level of <unk> . 
 This list of ceratopsian genera by classification and location follows a review by Thomas R. Holtz , Jr. in 2010 . 
 Ceratopsia 
 <unk> - ( Japan ) 
 <unk> - ( Shandong , eastern China ) 
 <unk> - ( Germany ) 
 Yinlong - ( Xinjiang , western China ) 
 Family <unk> 
 Chaoyangsaurus - ( <unk> , northeastern China ) 
 <unk> - ( Hebei , China ) 
 Family Psittacosauridae 
 Psittacosaurus - ( China & Mongolia ) 
 Neoceratopsia 
 <unk> - ( Gansu , northwestern China ) 
 Auroraceratops - ( Gansu , northwestern China ) 
 <unk> - ( <unk> , northwestern China ) 
 <unk> - ( South Korea ) 
 <unk> - ( Uzbekistan ) 
 <unk> - ( <unk> , northeastern China ) 
 <unk> - ( Mongolia ) 
 <unk> - ( central China ) 
 <unk> - ( Mongolia ) 
 Family Leptoceratopsidae 
 Asiaceratops - ( China , Mongolia , Uzbekistan ) 
 <unk> - ( Montana , US ) 
 <unk> - ( Alberta , Canada ) 
 <unk> - ( China ) 
 <unk> - ( Alberta , Canada & Wyoming , US ) 
 <unk> - ( Montana , US ) 
 <unk> - ( Montana , US ) 
 <unk> - ( Mongolia ) 
 <unk> - ( Alberta , Canada ) 
 <unk> - ( <unk> , China ) 
 Family <unk> 
 <unk> - ( Hungary ) 
 <unk> - ( Mongolia ) 
 <unk> - ( Mongolia ) 
 <unk> - ( Mongolia ) 
 <unk> - ( Mongolia ) 
 Family Protoceratopsidae 
 <unk> - ( Mongolia ) 
 <unk> - ( Mongolia ) 
 Magnirostris - ( Inner Mongolia , China ) 
 Protoceratops - ( Mongolia ) 
 <unk> Ceratopsoidea 
 Turanoceratops - ( Uzbekistan ) 
 Zuniceratops - ( New Mexico , US ) 
 Family Ceratopsidae 
 Subfamily <unk> 
 <unk> - ( Alberta , Canada & ? Montana , USA ) 
 <unk> - ( Montana , USA ) 
 <unk> - ( Montana , USA & Alberta , Canada ) 
 Centrosaurus - ( Alberta , Canada ) 
 <unk> - ( Alberta , Canada ) 
 <unk> - ( Utah , USA ) 
 Monoclonius - ( Montana , USA & Alberta , Canada ) 
 <unk> - ( Utah , USA ) 
 <unk> - ( Montana , USA ) 
 <unk> - ( Alberta , Canada ) 
 <unk> - ( Alberta , Canada & Montana , USA ) 
 <unk> - ( Alberta , Canada ) 
 Tribe <unk> 
 <unk> - ( Montana , USA ) 
 <unk> - ( Montana , USA ) 
 <unk> ( Alberta , Canada & Alaska , USA ) 
 <unk> - ( Shandong , China ) 
 Subfamily <unk> 
 Ceratops - ( Montana , USA & Alberta , Canada ) 
 Subfamily <unk> 
 Agathaumas - ( Wyoming , USA ) 
 <unk> - ( Texas , USA ) 
 <unk> - ( Alberta , Canada ) 
 <unk> - ( Alberta , Canada ) 
 Chasmosaurus - ( Alberta , Canada ) 
 <unk> - ( <unk> , Mexico ) 
 ? <unk> - ( Montana , USA ) 
 <unk> - ( Montana , USA ) 
 <unk> - ( Utah , USA ) 
 <unk> - ( Montana , USA ) 
 <unk> - ( Alberta & Saskatchewan , Canada ) 
 <unk> - ( New Mexico , USA ) 
 ? <unk> - ( Colorado , USA ) 
 <unk> - ( Utah , USA ) 
 <unk> - ( Alberta , Canada ) 
 Tribe <unk> 
 <unk> - ( Alberta , Canada ) 
 <unk> - ( Wyoming , USA ) 
 <unk> - ( New Mexico , USA ) 
 <unk> - ( Alberta , Canada ) 
 <unk> - ( South Dakota , USA ) 
 <unk> - ( New Mexico , USA ) 
 <unk> - ( Wyoming , Montana , South Dakota , North Dakota , & Utah , USA & Saskatchewan , Canada ) 
 Triceratops - ( Montana & Wyoming , USA & Saskatchewan & Alberta , Canada ) 
 Possible ceratopsians from the Southern Hemisphere include the Australian <unk> , known from an <unk> , and <unk> from Argentina is known from a single toothless jaw ( which has been lost ) . <unk> from the Late Cretaceous ( <unk> ) of Belgium may also be a ceratopsian , specifically a neoceratopsian closer to <unk> than <unk> . Possible leptoceratopsid remains have also been described from the early Campanian of Sweden . 
 
 = = = Phylogeny = = = 
 
 <unk> today agree on the overall structure of the ceratopsian family tree , although there are differences on individual taxa . There have been several cladistic studies performed on basal ceratopsians since 2000 . None have used every taxon listed above and many of the differences between the studies are still unresolved . 
 In clade @-@ based phylogenetic taxonomy , Ceratopsia is often defined to include all <unk> more closely related to Triceratops than to <unk> . Under this definition , the most basal known ceratopsians are Yinlong , from the Late Jurassic Period , along with Chaoyangsaurus and the family Psittacosauridae , from the Early Cretaceous Period , all of which were discovered in northern China or Mongolia . The rostral bone and flared <unk> are already present in all of these forms , indicating that even earlier ceratopsians remain to be discovered . 
 The clade Neoceratopsia includes all ceratopsians more derived than <unk> . Another subset of <unk> is called <unk> , which currently includes all ceratopsians more derived than Auroraceratops . <unk> show the first development of the neck frill and the fusion of the first several neck vertebrae to support the increasingly heavy head . Within <unk> , three groups are generally recognized , although the membership of these groups varies somewhat from study to study and some animals may not fit in any of them . One group can be called Protoceratopsidae and includes Protoceratops and its closest relatives , all Asian . Another group , Leptoceratopsidae , includes mostly North American animals that are more closely related to <unk> . The Ceratopsoidea includes animals like Zuniceratops , which are more closely related to the family Ceratopsidae . This last family includes Triceratops and all the large North American ceratopsians and is further divided into the subfamilies <unk> and <unk> ( also known as <unk> ) . 
 
 = = = = <unk> phylogeny = = = = 
 
 Andrew <unk> and his colleagues in 2014 published a description of a new neoceratopsian , Aquilops americanus , through the peer @-@ reviewed science journal <unk> <unk> . They analysed their taxa as well as most other primitive ceratopsians to get a consensus cladogram . They created their own data matrix and through it found that many groups of ceratopsians could be supported , and that Aquilops was a basal neoceratopsian that could potentially be a <unk> , leptoceratopsid , or ceratopsid , although any one of these groups would have a large ghost lineage with Aquilops . 
 Their study also found an equal consensus cladogram finding <unk> not as a neoceratopsian but a <unk> . Nothing else about the cladograms changed . 
 
 = = = = Xu / Makovicky / Chinnery Phylogeny = = = = 
 
 Xu <unk> of the Chinese Institute of <unk> <unk> and <unk> ( <unk> ) in Beijing , along with Peter Makovicky , formerly of the American Museum of Natural History ( AMNH ) in New York City and others , published a cladistic analysis in the 2002 description of <unk> . This analysis is very similar to one published by Makovicky in 2001 . Makovicky , who currently works at the Field Museum of Natural History in Chicago , also included this analysis in his 2002 doctoral thesis . Xu and other colleagues added Yinlong to this analysis in 2006 . 
 Brenda Chinnery , formerly of the Museum of the Rockies in Bozeman , Montana , independently described <unk> in 2005 and published a new phylogeny . In 2006 , Makovicky and Mark <unk> of the AMNH incorporated Chinnery 's analysis into their own and also added <unk> , although they were not able to include Yinlong . The cladogram presented below is a combination of Xu , Makovicky , and their colleagues ' most recent work . 
 Chaoyangsaurus is recovered in a more basal position than Psittacosauridae , although Chinnery 's original analysis finds it within Neoceratopsia . Protoceratopsidae is considered to be the sister group of Ceratopsoidea . The fragmentary Asiaceratops was included in these studies and is found to have a variable position , either as a basal neoceratopsian or as a leptoceratopsid , most likely due to the amount of missing information . <unk> of Asiaceratops <unk> the entire cladogram . 
 Makovicky 's latest analysis includes <unk> <unk> ( " <unk> " ) , a Late Jurassic ceratopsian from China that , at the time , was awaiting publication , but has since been published as <unk> . <unk> and Turanoceratops are considered nomina dubia in this study . Makovicky believes <unk> , Magnirostris , and <unk> to be junior synonyms of <unk> , and <unk> to be synonymous with Protoceratops . 
 
 = = = = You / Dodson Phylogeny = = = = 
 
 You <unk> of Beijing 's Chinese Academy of Geological Sciences , was a co @-@ author with Xu and Makovicky in 2002 but , in 2003 , he and Peter Dodson from the University of Pennsylvania published a separate analysis . The two presented this analysis again in 2004 . In 2005 , You and three others , including Dodson , published on Auroraceratops and inserted this new dinosaur into their phylogeny . 
 In contrast to the previous analysis , You and Dodson find Chaoyangsaurus to be the most basal neoceratopsian , more derived than Psittacosaurus , while Leptoceratopsidae , not Protoceratopsidae , is recovered as the sister group of Ceratopsidae . This study includes Auroraceratops , but lacks seven taxa found in Xu and Makovicky 's work , so it is unclear how comparable the two studies are . Asiaceratops and Turanoceratops are each considered nomina dubia and not included . Along with <unk> <unk> , You described Magnirostris in 2003 , but to date has not included it in any of his cladograms . 
 
 = = <unk> = = 
 
 
 = = = <unk> = = = 
 
 Ceratopsia appears to have originated in Asia , as all of the earliest members are found there . <unk> remains , including teeth , which appear to be neoceratopsian , are found in North America from the <unk> stage ( 112 to 100 million years ago ) , indicating that the group had dispersed across what is now the Bering Strait by the middle of the Cretaceous Period . Almost all <unk> are North American , aside from <unk> , which may represent a separate dispersal event , back into Asia . <unk> 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 <unk> 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 . 
 
 = = = Individual variation = = = 
 
 Unlike almost all other dinosaur groups , skulls are the most commonly preserved elements of ceratopsian skeletons and many species are known only from skulls . There is a great deal of variation between and even within ceratopsian species . Complete growth series from embryo to adult are known for Psittacosaurus and Protoceratops , allowing the study of <unk> variation in these species . Significant sexual <unk> has been noted in Protoceratops and several ceratopsids . 
 
 = = = 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 / <unk> 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 <unk> 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 . 
 Although ceratopsians are generally considered herbivorous , a few paleontologists , such as Darren <unk> and Mark <unk> , have speculated online that at least some ceratopsians may have been <unk> omnivorous . 
 
 = = = <unk> and <unk> = = = 
 
 Most restorations of ceratopsians show them with erect hindlimbs but semi @-@ sprawling forelimbs , which suggest that they were not fast <unk> . But Paul and Christiansen ( 2000 ) argued that at least the later ceratopsians had upright forelimbs and the larger species may have been as fast as <unk> , which can run at up to 56 km or 35 miles per hour . 
 
 = = = Daily activity patterns = = = 
 
 A nocturnal lifestyle has been suggested for the primitive ceratopsian Protoceratops . However , comparisons between the <unk> rings of Protoceratops and Psittacosaurus and modern birds and reptiles indicate that they may have been <unk> , active throughout the day at short intervals . 
 
 = = = <unk> = = = 
 
 <unk> @-@ related bone fractures have been documented in ceratopsians . <unk> has also been documented in the shoulder blade of a ceratopsian . 
 
 = = Timeline of genera = = 
 
 
 