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Ceratopsia or Ceratopia ( or ; Greek: "horned faces") is a group of herbivorous, beaked
dinosaur Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the evolution of dinosaurs is t ...
s that thrived in what are now
North America North America is a continent in the Northern Hemisphere and almost entirely within the Western Hemisphere. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South America and th ...
,
Europe Europe is a large peninsula conventionally considered a continent in its own right because of its great physical size and the weight of its history and traditions. Europe is also considered a Continent#Subcontinents, subcontinent of Eurasia ...
, and
Asia Asia (, ) is one of the world's most notable geographical regions, which is either considered a continent in its own right or a subcontinent of Eurasia, which shares the continental landmass of Afro-Eurasia with Africa. Asia covers an are ...
, during the
Cretaceous The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of ...
Period, although ancestral forms lived earlier, in the
Jurassic The Jurassic ( ) is a geologic period and stratigraphic system that spanned from the end of the Triassic Period million years ago (Mya) to the beginning of the Cretaceous Period, approximately Mya. The Jurassic constitutes the middle period of ...
. The earliest known ceratopsian, '' Yinlong downsi'', lived between 161.2 and 155.7 million years ago.Holtz, Thomas R. Jr. (2011) ''Dinosaurs: The Most Complete, Up-to-Date Encyclopedia for Dinosaur Lovers of All Ages,'
Winter 2010 Appendix.
/ref> The last ceratopsian species, '' Triceratops prorsus'', became extinct during the
Cretaceous–Paleogene extinction event The Cretaceous–Paleogene (K–Pg) extinction event (also known as the Cretaceous–Tertiary extinction) was a sudden mass extinction of three-quarters of the plant and animal species on Earth, approximately 66 million years ago. With the ...
, . ''Triceratops'' is by far the best-known ceratopsian to the general public. It is traditional for ceratopsian
genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nom ...
names to end in "''-ceratops''", 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 In binomial nomenclature, a ''nomen dubium'' (Latin for "doubtful name", plural ''nomina dubia'') is a scientific name that is of unknown or doubtful application. Zoology In case of a ''nomen dubium'' it may be impossible to determine whether a s ...
'' today as its fossil remains have no distinguishing characteristics that are not also found in other ceratopsians.Dodson, P. 1996. ''The Horned Dinosaurs''. Princeton: Princeton University Press. 346pp.


Description

Early members of the ceratopsian group, such as '' Psittacosaurus'', were small bipedal animals. Later members, including
ceratopsids Ceratopsidae (sometimes spelled Ceratopidae) is a family of ceratopsian dinosaurs including ''Triceratops'', ''Centrosaurus'', and ''Styracosaurus''. All known species were quadrupedal herbivores from the Upper Cretaceous. All but one species ar ...
like '' Centrosaurus'' and ''
Triceratops ''Triceratops'' ( ; ) is a genus of herbivorous chasmosaurine ceratopsid dinosaur that first appeared during the late Maastrichtian stage of the Late Cretaceous period, about 68 million years ago in what is now North America. It is one ...
'', became very large quadrupeds 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,
thermoregulation Thermoregulation is the ability of an organism to keep its body temperature within certain boundaries, even when the surrounding temperature is very different. A thermoconforming organism, by contrast, simply adopts the surrounding temperatur ...
, the attachment of large neck and chewing muscles or some combination of the above. Ceratopsians ranged in size from 1 meter (3 ft) and 23 kilograms (50 lb) to over 9 meters (30 ft) and 9,100 kg (20,100 lb). Ceratopsians are easily recognized by features of the
skull The skull is a bone protective cavity for the brain. The skull is composed of four types of bone i.e., cranial bones, facial bones, ear ossicles and hyoid bone. However two parts are more prominent: the cranium and the mandible. In humans, th ...
. On the tip of a ceratopsian upper jaw is the rostral bone, an edentulous (toothless) ossification, unique to ceratopsians.
Othniel Charles Marsh Othniel Charles Marsh (October 29, 1831 – March 18, 1899) was an American professor of Paleontology in Yale College and President of the National Academy of Sciences. He was one of the preeminent scientists in the field of paleontology. Among ...
recognized and named this bone, which acts as a mirror image of the predentary bone on the lower jaw. This ossification evolved to morphologically aid the mastication of plant matter. Along with the predentary 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 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 the parietal and squamosal bones of the skull roof, to form the neck frill.You H. & Dodson, P. 2004. Basal Ceratopsia. In: Weishampel, D.B., Dodson, P., & Osmolska, H. (Eds.). ''The Dinosauria'' (2nd Edition). Berkeley: University of California Press. Pp. 478-493.Dodson, P., Forster, C.A., & Sampson, S.D. 2004. Ceratopsidae. In: Dodson, P., Weishampel, D.B., & Osmolska, H. (Eds.). ''The Dinosauria'' (2nd Edition). Berkeley: University of California Press. Pp. 494-513. The epoccipital is a distinctive
bone A bone is a rigid organ that constitutes part of the skeleton in most vertebrate animals. Bones protect the various other organs of the body, produce red and white blood cells, store minerals, provide structure and support for the body, ...
found lining the frills of ceratopsid ceratopsians. The name is a misnomer, as they are not associated with the occipital bone. Epoccipitals begin as separate bones that
fuse Fuse or FUSE may refer to: Devices * Fuse (electrical), a device used in electrical systems to protect against excessive current ** Fuse (automotive), a class of fuses for vehicles * Fuse (hydraulic), a device used in hydraulic systems to protect ...
during the animal's growth to either the squamosal or parietal bones that make up the base of the frill. These bones were ornamental instead of functional, and may have helped differentiate
species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriat ...
. 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 Chasmosaurinae is a subfamily of ceratopsid dinosaurs. They were one of the most successful groups of herbivores of their time. Chasmosaurines appeared in the early Campanian, and became extinct, along with all other non-avian dinosaurs, during t ...
), 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, like '' Centrosaurus'', '' Pachyrhinosaurus'', and ''
Styracosaurus ''Styracosaurus'' ( ; meaning "spiked lizard" from the Ancient Greek / "spike at the butt-end of a spear-shaft" and / "lizard") is a genus of herbivorous ceratopsian dinosaur from the Cretaceous Period (Campanian stage), about 75.5 to 74.5 ...
'', 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 of ''
Triceratops ''Triceratops'' ( ; ) is a genus of herbivorous chasmosaurine ceratopsid dinosaur that first appeared during the late Maastrichtian stage of the Late Cretaceous period, about 68 million years ago in what is now North America. It is one ...
''. When regarding the ossification's morphogenetic traits, it can be described as dermal. The term epoccipital was coined by famous paleontologist
Othniel Charles Marsh Othniel Charles Marsh (October 29, 1831 – March 18, 1899) was an American professor of Paleontology in Yale College and President of the National Academy of Sciences. He was one of the preeminent scientists in the field of paleontology. Among ...
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 A geologist is a scientist who studies the solid, liquid, and gaseous matter that constitutes Earth and other terrestrial planets, as well as the processes that shape them. Geologists usually study geology, earth science, or geophysics, althou ...
F.V. Hayden. Teeth discovered during an 1855 expedition to
Montana Montana () is a state in the Mountain West division of the Western United States. It is bordered by Idaho to the west, North Dakota and South Dakota to the east, Wyoming to the south, and the Canadian provinces of Alberta, British Columb ...
were first assigned to
hadrosaurid Hadrosaurids (), or duck-billed dinosaurs, are members of the ornithischian family Hadrosauridae. This group is known as the duck-billed dinosaurs for the flat duck-bill appearance of the bones in their snouts. The ornithopod family, which inclu ...
s and included within the genus '' Trachodon''. It was not until the early 20th century that some of these were recognized as ceratopsian teeth.Hatcher, J.B., Marsh, O.C. and Lull, R.S. (1907). ''The Ceratopsia''. Government Printing Office, Washington, D.C., 300 pp. During another of Hayden's expeditions in 1872, Fielding Bradford Meek found several giant bones protruding from a hillside in southwestern
Wyoming Wyoming () is a state in the Mountain West subregion of the Western United States. It is bordered by Montana to the north and northwest, South Dakota and Nebraska to the east, Idaho to the west, Utah to the southwest, and Colorado to t ...
. He alerted
paleontologist Paleontology (), also spelled palaeontology or palæontology, is the scientific study of life that existed prior to, and sometimes including, the start of the Holocene epoch (roughly 11,700 years before present). It includes the study of fossi ...
Edward Drinker Cope Edward Drinker Cope (July 28, 1840 – April 12, 1897) was an American zoologist, paleontologist, comparative anatomist, herpetologist, and ichthyologist. Born to a wealthy Quaker family, Cope distinguished himself as a child prodigy interes ...
, 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 sylvestris'', meaning "marvellous forest-dweller".Gillette, D.D. (1999). ''Vertebrate Paleontology In Utah''. Utah Geological Survey, 554 pp. , Soon after, Cope named two more dinosaurs that would eventually come to be recognized as ceratopsids: ''
Polyonax ''Polyonax'' (meaning "master over many") was a genus of ceratopsid dinosaur from the late Maastrichtian-age Upper Cretaceous Denver Formation of Colorado, United States. Founded upon poor remains, it is today regarded as a dubious name. Hi ...
'' and '' Monoclonius''. ''Monoclonius'' was notable for the number of disassociated remains found, including the first evidence of ceratopsid horns and frills. Several ''Monoclonius'' fossils were found by Cope, assisted by
Charles Hazelius Sternberg Charles Hazelius Sternberg (June 15, 1850 – July 20, 1943) was an American fossil collector and paleontologist. He was active in both fields from 1876 to 1928, and collected fossils for Edward Drinker Cope and Othniel C. Marsh, and for the ...
, in summer 1876 near the
Judith River The Judith River is a tributary of the Missouri River, approximately 124 mi (200 km) long, running through central Montana in the United States. It rises in the Little Belt Mountains and flows northeast past Utica and Hobson. It is ...
in
Chouteau County Chouteau County is a county located in the North-Central region of the U.S. state of Montana. As of the 2020 census, the population was 5,895. Its county seat is Fort Benton. The county was established in 1865 as one of the original nine cou ...
, 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 Marsh Othniel Charles Marsh (October 29, 1831 – March 18, 1899) was an American professor of Paleontology in Yale College and President of the National Academy of Sciences. He was one of the preeminent scientists in the field of paleontology. Among ...
described the first well preserved horned dinosaurs, '' Ceratops'' and ''
Triceratops ''Triceratops'' ( ; ) is a genus of herbivorous chasmosaurine ceratopsid dinosaur that first appeared during the late Maastrichtian stage of the Late Cretaceous period, about 68 million years ago in what is now North America. It is one ...
''. In 1890 Marsh classified them together in the family Ceratopsidae and the order Ceratopsia. This prompted Cope to reexamine his own specimens and to realize that ''Triceratops'', ''Monoclonius'', and ''Agathaumas'' all represented a single group of similar dinosaurs, which he named Agathaumidae in 1891. Cope redescribed ''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 Othniel Charles Marsh (October 29, 1831 – March 18, 1899) was an American professor of Paleontology in Yale College and President of the National Academy of Sciences. He was one of the preeminent scientists in the field of paleontology. Among ...
in 1890 to include dinosaurs possessing certain characteristic features, including horns, a rostral bone, teeth with two
roots A root is the part of a plant, generally underground, that anchors the plant body, and absorbs and stores water and nutrients. Root or roots may also refer to: Art, entertainment, and media * ''The Root'' (magazine), an online magazine focusing ...
, fused neck
vertebra The spinal column, a defining synapomorphy shared by nearly all vertebrates, Hagfish are believed to have secondarily lost their spinal column is a moderately flexible series of vertebrae (singular vertebra), each constituting a characteristi ...
e, and a forward-oriented pubis. Marsh considered the group distinct enough to warrant its own suborder within Ornithischia. The name is derived from the Greek ''κέρας''/''kéras'' meaning 'horn' and ''ὄψῐς''/''ópsis'' meaning 'appearance, view' and by extension 'face'. As early as the 1960s, it was noted that the name ''Ceratopsia'' is actually incorrect
linguistically Linguistics is the scientific study of human language. It is called a scientific study because it entails a comprehensive, systematic, objective, and precise analysis of all aspects of language, particularly its nature and structure. Linguis ...
and that it should be ''Ceratopia''.Steel, R. 1969. Ornithischia. In: Kuhn, O. (Ed.). ''Handbuch de Paleoherpetologie'' (Part 15). Stuttgart: Gustav Fischer Verlag. 87pp. However, this spelling, while technically correct, has been used only rarely in the scientific literature, and the vast majority of
paleontologist Paleontology (), also spelled palaeontology or palæontology, is the scientific study of life that existed prior to, and sometimes including, the start of the Holocene epoch (roughly 11,700 years before present). It includes the study of fossi ...
s continue to use Ceratopsia. As the ICZN does not govern taxa above the level of
superfamily SUPERFAMILY is a database and search platform of structural and functional annotation for all proteins and genomes. It classifies amino acid sequences into known structural domains, especially into SCOP superfamilies. Domains are functional, str ...
, 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.Benton, M.J. (2004). ''Vertebrate Palaeontology, Third Edition''. Blackwell Publishing, 472 pp.


Phylogeny

In
clade A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. Rather than the English ter ...
-based phylogenetic taxonomy, Ceratopsia is often defined to include all marginocephalians more closely related to ''Triceratops'' than to '' Pachycephalosaurus''. Under this definition, the most basal known ceratopsians are '' Yinlong'', from the Late
Jurassic The Jurassic ( ) is a geologic period and stratigraphic system that spanned from the end of the Triassic Period million years ago (Mya) to the beginning of the Cretaceous Period, approximately Mya. The Jurassic constitutes the middle period of ...
Period, along with '' Chaoyangsaurus'' and the family Psittacosauridae, from the Early
Cretaceous The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of ...
Period, all of which were discovered in northern
China China, officially the People's Republic of China (PRC), is a country in East Asia. It is the world's List of countries and dependencies by population, most populous country, with a Population of China, population exceeding 1.4 billion, slig ...
or
Mongolia Mongolia; Mongolian script: , , ; lit. "Mongol Nation" or "State of Mongolia" () is a landlocked country in East Asia, bordered by Russia to the north and China to the south. It covers an area of , with a population of just 3.3 million ...
. The rostral bone and flared jugals are already present in all of these forms, indicating that even earlier ceratopsians remain to be discovered. The
clade A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. Rather than the English ter ...
Neoceratopsia includes all ceratopsians more
derived Derive may refer to: *Derive (computer algebra system), a commercial system made by Texas Instruments * ''Dérive'' (magazine), an Austrian science magazine on urbanism *Dérive, a psychogeographical concept See also * *Derivation (disambiguation ...
than psittacosaurids. Another subset of neoceratopsians is called Coronosauria, which either includes all ceratopsians more derived than '' Auroraceratops'', or more derived than Leptoceratopsidae. Coronosaurs show the first development of the neck frill and the fusion of the first several neck
vertebra The spinal column, a defining synapomorphy shared by nearly all vertebrates, Hagfish are believed to have secondarily lost their spinal column is a moderately flexible series of vertebrae (singular vertebra), each constituting a characteristi ...
e to 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 called Protoceratopsidae and includes '' Protoceratops'' and its closest relatives, all Asian. Another group, Leptoceratopsidae, includes mostly
North America North America is a continent in the Northern Hemisphere and almost entirely within the Western Hemisphere. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South America and th ...
n animals that are more closely related to '' Leptoceratops''. The third group, Ceratopsoidea, includes the family Ceratopsidae and closely related animals like '' Zuniceratops''. Ceratopsidae itself includes ''Triceratops'' and all the large North American ceratopsians and is further divided into the subfamilies Centrosaurinae and
Chasmosaurinae Chasmosaurinae is a subfamily of ceratopsid dinosaurs. They were one of the most successful groups of herbivores of their time. Chasmosaurines appeared in the early Campanian, and became extinct, along with all other non-avian dinosaurs, durin ...
. All previously published neoceratopsian phylogenetic analyses were incorporated into the analysis of Eric M. Morschhauser and colleagues in 2019, along with all previously published diagnostic species excluding the incomplete juvenile '' Archaeoceratops yujingziensis'' and the problematic genera '' Bainoceratops'', '' Lamaceratops'', '' Platyceratops'' and '' Gobiceratops'' that are very closely related to and potentially synonymous with '' Bagaceratops''. 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.


Paleobiology

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 An embryo is an initial stage of development of a multicellular organism. In organisms that reproduce sexually, embryonic development is the part of the life cycle that begins just after fertilization of the female egg cell by the male spe ...
to adult are known for ''Psittacosaurus'' and ''Protoceratops'', allowing the study of ontogenetic variation in 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 as rhinos, which can run at up to 56 km or 35 miles per hour. A
nocturnal Nocturnality is an animal behavior characterized by being active during the night and sleeping during the day. The common adjective is "nocturnal", versus diurnal meaning the opposite. Nocturnal creatures generally have highly developed sens ...
lifestyle has been suggested for the primitive ceratopsian '' Protoceratops''. However, comparisons between the
scleral ring Sclerotic rings are rings of bone found in the eyes of many animals in several groups of vertebrates, except for mammals and crocodilians. They can be made up of single bones or multiple segments and take their name from the sclera. They are beli ...
s of ''Protoceratops'' and '' Psittacosaurus'' and modern birds and reptiles indicate that they may have been cathemeral, active throughout the day at short intervals.


Paleoecology


Paleobiogeography

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 the Albian 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 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 Endemism is the state of a species being found in a single defined geographic location, such as an island, state, nation, country or other defined zone; organisms that are indigenous to a place are not endemic to it if they are also found else ...
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
Australia Australia, officially the Commonwealth of Australia, is a sovereign country comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands. With an area of , Australia is the largest country by ...
n '' Serendipaceratops'', known from an ulna, and ''
Notoceratops ''Notoceratops'' (meaning "southern horned face") is a nomen dubium, dubious genus of extinct ornithischian dinosaur based on an incomplete, toothless left dentary (now lost) from the Late Cretaceous of Patagonia (in Argentina), probably dating t ...
'' from
Argentina Argentina (), officially the Argentine Republic ( es, link=no, República Argentina), is a country in the southern half of South America. Argentina covers an area of , making it the List of South American countries by area, second-largest ...
is known from a single toothless jaw (which has been lost).Rich, T.H. & Vickers-Rich, P. 2003. Protoceratopsian? ulnae from the Early Cretaceous of Australia. ''Records of the Queen Victoria Museum.'' No. 113. '' Craspedodon'' from the
Late Cretaceous The Late Cretaceous (100.5–66 Ma) is the younger of two epochs into which the Cretaceous Period is divided in the geologic time scale. Rock strata from this epoch form the Upper Cretaceous Series. The Cretaceous is named after ''creta'', ...
(
Santonian The Santonian is an age in the geologic timescale or a chronostratigraphic stage. It is a subdivision of the Late Cretaceous Epoch or Upper Cretaceous Series. It spans the time between 86.3 ± 0.7 mya (million years ago) and 83.6 ± 0.7 mya. ...
) of
Belgium Belgium, ; french: Belgique ; german: Belgien officially the Kingdom of Belgium, is a country in Northwestern Europe. The country is bordered by the Netherlands to the north, Germany to the east, Luxembourg to the southeast, France to ...
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 Sweden, formally the Kingdom of Sweden,The United Nations Group of Experts on Geographical Names states that the country's formal name is the Kingdom of SwedenUNGEGN World Geographical Names, Sweden./ref> is a Nordic countries, Nordic c ...
.


Ecological role

''Psittacosaurus'' and ''Protoceratops'' are the most common dinosaurs in the different Mongolian
sediments Sediment is a naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of wind, water, or ice or by the force of gravity acting on the particles. For example, sa ...
where they are found. ''Triceratops''
fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...
s 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 Fauna is all of the animal life present in a particular region or time. The corresponding term for plants is '' flora'', and for fungi, it is '' funga''. Flora, fauna, funga and other forms of life are collectively referred to as '' biota''. ...
in some areas.Bakker, R.T. (1986). ''The Dinosaur Heresies: New Theories Unlocking The Mystery of the Dinosaurs and Their Extinction''. William Morrow:New York, p. 438. 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
herd A herd is a social group of certain animals of the same species, either wild or domestic. The form of collective animal behavior associated with this is called '' herding''. These animals are known as gregarious animals. The term ''herd'' i ...
s. 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

at Palaeos.com (technical) {{Taxonbar, from=Q131381 Marginocephalians Late Jurassic first appearances Maastrichtian extinctions Taxa named by Othniel Charles Marsh