Ceratopsia

Not to be confused withCeratosauria.

Ceratopsians Temporal range:Late Jurassic–Late Cretaceous,
Triceratopsskeleton,American Museum of Natural History
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Clade:	Dinosauria
Clade:	†Ornithischia
Clade:	†Neornithischia
Clade:	†Marginocephalia
Clade:	†Ceratopsia Marsh,1890
Type species
†Ceratops montanus Marsh,1888
Subgroups
†Ajkaceratops? †Albalophosaurus? †Micropachycephalosaurus? †Psittacosaurus †Stenopelix? †Chaoyangsauridae †NeoceratopsiaSereno, 1986 †Aquilops †Auroraceratops †Beg †Craspedodon? †Graciliceratops †Koreaceratops †Kulceratops †Liaoceratops †Microceratus †Mosaiceratops †Notoceratops? †Sasayamagnomus †Serendipaceratops? †Archaeoceratopsidae †Archaeoceratops †?Helioceratops †?Yamaceratops †EuceratopsiaMadziaet al.,2021 †Leptoceratopsidae †CoronosauriaSereno, 1986 †Protoceratopsidae †CeratopsoideaHay, 1902sensuSereno, 1998 †CeratopsomorphaWolfe & Kirkland, 1998 †Turanoceratops †Zuniceratops †Ceratopsidae

CeratopsiaorCeratopia(/ˌsɛrəˈtɒpsiə/or/ˌsɛrəˈtoʊpiə/;Greek:"horned faces" ) is a group ofherbivorous,beakeddinosaursthat thrived in what are nowNorth America,Europe,andAsia,during theCretaceousPeriod,although ancestral forms lived earlier, in theJurassic.The earliest known ceratopsian,Yinlong downsi,lived between 161.2 and 155.7 million years ago.The last ceratopsian species,Triceratops prorsus,became extinct during theCretaceous–Paleogene extinction event,66million years ago.

Triceratopsis by far the best-known ceratopsian to the general public. It is traditional for ceratopsiangenusnames to end in "-ceratops",although this is not always the case. One of the first named genera wasCeratopsitself, which lent its name to the group, although it is considered anomen dubiumtoday as its fossil remains have no distinguishing characteristics that are not also found in other ceratopsians.

Description

Centrosaurus,with large nasal horn and bony processes over the front of thefrill.Museum of Victoria.

Early members of the ceratopsian group, such asPsittacosaurus,were smallbipedalanimals. Later members, includingceratopsidslikeCentrosaurusandTriceratops,became very largequadrupedsand developed elaborate facialhornsand frills extending over the neck. While these frills might have served to protect the vulnerable neck frompredators,they may also have been used fordisplay,thermoregulation,the attachment of large neck and chewing muscles or some combination of the above. Ceratopsians ranged in size from 1 meter (3.3 feet) and 23 kilograms (51 pounds) to over 9 meters (30 feet) and 9,100 kg (20,100 lb).

Ceratopsians are easily recognized by features of theskull.On the tip of a ceratopsian upper jaw is the rostral bone, an edentulous (toothless) ossification, unique to ceratopsians.Othniel Charles Marshrecognized and named this bone, which acts as a mirror image of thepredentarybone on the lower jaw. This ossification evolved to morphologically aid the chewing of plant matter.Along with thepredentarybone, which forms the tip of the lower jaw in allornithischians,the rostral forms a superficiallyparrot-like beak. Also, thejugalbones below the eye are prominent, flaring out sideways to make the skull appear somewhat triangular when viewed from above. This triangular appearance is accentuated in later ceratopsians by the rearwards extension of theparietalandsquamosalbones of the skull roof, to form the neck frill.

Known skin integument of several ceratopsians

The neck frills of ceratopsids are surrounded by theepoccipital bones.The name is a misnomer, as they are not associated with theoccipital bone.Epoccipitals begin as separate bones thatfuseduring the animal's growth to either thesquamosalorparietalbones that make up the base of the frill. These bones were ornamental instead of functional, and may have helped differentiatespecies.Epoccipitals probably were present in all known ceratopsids.They appear to have been broadly different between short-frilled ceratopsids (centrosaurines) and long-frilled ceratopsids (chasmosaurines), being elliptical with constricted 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 centrosaurines especially, likeCentrosaurus,Pachyrhinosaurus,andStyracosaurus,these bones become long and spike- or hook-like.A well-known example is the coarse sawtooth fringe of broad triangular epoccipitals on the frill ofTriceratops.When regarding the ossification's morphogenetic traits, it can be described as dermal. The termepoccipitalwas coined by paleontologistOthniel Charles Marshin 1889.

History of study

Main article:Timeline of ceratopsian research

Agathaumaswas the first recognized genus of ceratopsian

The first ceratopsian remains known to science were discovered during the U.S. Geological and Geographical Survey of the Territories led by the AmericangeologistF.V. Hayden.Teeth discovered during an 1855 expedition toMontanawere first assigned tohadrosauridsand included within the genusTrachodon.It was not until the early 20th century that some of these were recognized as ceratopsian teeth.During another of Hayden's expeditions in 1872,Fielding Bradford Meekfound several giant bones protruding from a hillside in southwesternWyoming.He alertedpaleontologistEdward Drinker 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 speciesAgathaumas sylvestris,meaning "marvellous forest-dweller".Soon after, Cope named two more dinosaurs that would eventually come to be recognized as ceratopsids:PolyonaxandMonoclonius.Monocloniuswas notable for the number of disassociated remains found, including the first evidence of ceratopsid horns and frills. SeveralMonocloniusfossils were found by Cope, assisted byCharles Hazelius Sternberg,in summer 1876 near theJudith RiverinChouteau 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 breastbone.

In 1888 and 1889,Othniel Charles Marshdescribed the first well preserved horned dinosaurs,CeratopsandTriceratops.In 1890 Marsh classified them together in the familyCeratopsidaeand the order Ceratopsia. This prompted Cope to reexamine his own specimens and to realize thatTriceratops,Monoclonius,andAgathaumasall represented a single group of similar dinosaurs, which he namedAgathaumidaein 1891. Cope redescribedMonocloniusas a horned dinosaur, with a large nasal horn and two smaller horns over the eyes, and a largefrill.

Classification

Psittacosaurus,an early ceratopsian

Prenoceratops,a leptoceratopsid

Protoceratops,a protoceratopsid

Styracosaurus,a centrosaurine ceratopsid

Triceratops,a chasmosaurinae ceratopsid and one of the last and largest ceratopsians

Ceratopsia was coined byOthniel Charles Marshin 1890 to include dinosaurs possessing certain characteristic features, including horns, arostral bone,teeth with tworoots,fused neckvertebrae,and a forward-orientedpubis.Marsh considered the group distinct enough to warrant its own suborder within Ornithischia.The name is derived from theGreekκέρας/kérasmeaning 'horn' andὄψῐς/ópsismeaning 'appearance, view' and by extension 'face'. As early as the 1960s, it was noted that the nameCeratopsiais actually incorrectlinguisticallyand that it should beCeratopia.However, this spelling, while technically correct, has been used only rarely in the scientific literature, and the vast majority ofpaleontologistscontinue to use Ceratopsia. As theICZNdoes not govern taxa above the level ofsuperfamily,this is unlikely to change.

Following Marsh, Ceratopsia has usually been classified as a suborder within the order Ornithischia. 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 infraorder.

Phylogeny

Ceratopsid skulls at theNatural History Museum of Utah

Inclade-basedphylogenetic taxonomy,Ceratopsia is often defined to include allmarginocephaliansmore closely related toTriceratopsthan toPachycephalosaurus.Under this definition, the mostbasalknown ceratopsians areYinlong,from the LateJurassicPeriod, along withChaoyangsaurusand the familyPsittacosauridae,from the EarlyCretaceousPeriod, all of which were discovered in northernChinaorMongolia.The rostral bone and flared jugals are already present in all of these forms, indicating that even earlier ceratopsians remain to be discovered.

ThecladeNeoceratopsiaincludes all ceratopsians morederivedthan psittacosaurids. Another subset of neoceratopsians is calledCoronosauria,which either includes all ceratopsians more derived thanAuroraceratops,or more derived thanLeptoceratopsidae.Coronosaurs show the first development of the neck frill and the fusion of the first several neckvertebraeto support the increasingly heavy head. Within Coronosauria, three groups are generally recognized, although the membership of these groups varies somewhat from study to study and some coronosaurs may not fit in any of them. One group can be calledProtoceratopsidaeand includesProtoceratopsand its closest relatives, all Asian. Another group,Leptoceratopsidae,includes mostlyNorth Americananimals that are more closely related toLeptoceratops.The third group,Ceratopsoidea,includes the familyCeratopsidaeand closely related animals likeZuniceratops.Ceratopsidae itself includesTriceratopsand all the large North American ceratopsians and is further divided into the subfamiliesCentrosaurinaeandChasmosaurinae.

All previously published neoceratopsian phylogenetic analyses were incorporated into the analysis of Eric M. Morschhauser and colleagues in2019,along with all previously published diagnostic species excluding the incomplete juvenileArchaeoceratops yujingziensisand the problematic generaBainoceratops,Lamaceratops,PlatyceratopsandGobiceratopsthat are very closely related to and potentially synonymous withBagaceratops.While there were many unresolved areas of the strict consensus, including all of Leptoceratopsidae, a single most parsimonious tree was found that was most consistent with the relative ages of the taxa included, which is shown below.

Ceratopsia

Psittacosaurus Psittacosaurus sinensis Psittacosaurus mongoliensis Neoceratopsia Chaoyangsauridae Yinlong downsi Chaoyangsaurus youngi Hualianceratops wucaiwanensis Xuanhuaceratops niei Stenopelix valdensis Liaoceratops yanzigouensis Archaeoceratops oshimai Aquilops americanus Auroraceratops rugosus Graciliceratops mongoliensis Asiaceratops salsopaludalis Mosaiceratops azumai Yamaceratops dorngobiensis Leptoceratopsidae Helioceratops brachygnathus Leptoceratops gracilis Ischioceratops zhuchengensis Prenoceratops pieganensis Udanoceratops tchizhovi Zhuchengceratops inexpectus Koreaceratops hwaseongensis Montanoceratops cerorhynchus Cerasinops hodgskissi Gryphoceratops morrisoni Unescoceratops kopelhusae Coronosauria Protoceratopsidae Bagaceratops rozhdestvenskyi Magnirostris dodsoni Protoceratops Protoceratops hellenikorhinus Protoceratops andrewsi Ceratopsoidea Ajkaceratops kozmai Zuniceratops christopheri Turanoceratops tardabilis Diabloceratops eatoni Ceratopsidae

Paleobiology

Protoceratopsgrowth series

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 fromembryoto adult are known forPsittacosaurusandProtoceratops,allowing the study ofontogenetic variationin these species.

Most restorations of ceratopsians show them with erect hindlimbs but semi-sprawling forelimbs, which suggest that they were not fast movers. But Paul and Christiansen (2000) argued that at least the later ceratopsians had upright forelimbs and the larger species may have been as fast asrhinos,which can run at up to 56 km or 35 miles per hour.

Anocturnallifestyle has been suggested for the primitive ceratopsianProtoceratops.However, comparisons between thescleral ringsofProtoceratopsandPsittacosaurusand modern birds and reptiles indicate that they may have beencathemeral,active throughout the day at short intervals.

Paleoecology

Paleobiogeography

Ceratopsian fossil discoveries. The presence of Jurassic ceratopsians only in Asia indicates an Asian origin for the group, while the more derived ceratopsids occur only in North America save for one Asian species. Questionable remains are indicated withquestion marks.

Ceratopsia appears to have originated in Asia, as all of the earliest members are found there. Fragmentary remains, including teeth, which appear to be neoceratopsian, are found in North America from theAlbianstage (112 to 100 million years ago), indicating that the group haddispersedacross what is now theBering Straitby the middle of the Cretaceous Period.Almost all leptoceratopsids are North American, aside fromUdanoceratops,which may represent a separate dispersal event, back into Asia. Ceratopsids and their immediate ancestors, such asZuniceratops,were unknown outside of western North America, and were presumedendemicto 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 formTuranoceratops,which may it as a ceratopsid. It is unknown whether this would indicates ceratopsids actually originated in Asia, or if theTuranoceratopsimmigrated from North America.

Possible ceratopsians from the Southern Hemisphere include theAustralianSerendipaceratops,known from anulna,andNotoceratopsfromArgentinais known from a single toothless jaw (which has been lost).Craspedodonfrom theLate Cretaceous(Santonian) ofBelgiummay also be a ceratopsian, specifically a neoceratopsian closer to ceratopsoidea than protoceratopsidae.Possible leptoceratopsid remains have also been described from the earlyCampanianofSweden.

Ecological role

PsittacosaurusandProtoceratopsare the most common dinosaurs in the different Mongoliansedimentswhere they are found.Triceratopsfossilsare 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 dinosaurfaunain some areas.These facts indicate that some ceratopsians were the dominant herbivores in their environments.

Some species of ceratopsians, especiallyCentrosaurusand its relatives, appear to have been gregarious, living inherds.This is suggested bybonebedfinds 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.

External links

• Dinosaurs portal
• Introduction to the Ceratopsians,University of California Museum of Paleontology
• Marginocephaliaat Palaeos.com (technical)