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Ceratopsia, meaning "horned faces", is an infraorder of quadrupedal herbivorous ornithischian dinosaurs. Ceratopsians 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). The group first appeared during the late Jurassic in Asia and evolved from bipedal ancestral forms. These basal ceratopsians, such as Psittacosaurus and Yinlong, possessed prominent bumps and ridges over the nose and eyes which would later develop into the elaborate displays found in late Cretaceous forms. By the middle of the Cretaceous period had dispersed across what is now the Bering Strait into North America. Possible late Cretaceous forms have been found in southern Australia, Europe, and South America. As the group entered the late Cretaceous many forms, including ceratopsids like Centrosaurus and Triceratops, evolved large and elaborate head displays with large horns and frills. While the frill might have served to protect the vulnerable neck from predators, it may also have been used for display, thermoregulation, the attachment of large neck and chewing muscles or some combination of the above. Ceratopsians became extinct, along with most other life forms, during the Cretaceous–Paleogene extinction event 65.5 million years ago.

Ceratopsian remains were first discovered in southwestern Wyoming in 1872 by Fielding Bradford Meek. Agathaumas was described that same year from these remains by Edward Drinker Cope, and was the first ceratopsian genus to be described. Ceratopsia was coined by Cope's rival, Othniel Charles Marsh, in 1890. Another early described genus was Ceratops, which lent its name to the group, although it and Agathaumas are considered a nomen dubium today. Triceratops is by far the best-known ceratopsian to the general public.

All ceratopsians possess a rostral bone, which is the basis for the parrot-like beak. Ceratopsians are a wide-ranging group, and several families exist. Basal forms include leptoceratopsids, psittacosaurids, and protoceratopsids. More derived forms include the late Cretaceous ceratopsids, which grew to enormous sizes. While herbivorous, many ceratopsians, especially basal forms, may have been omnivorous. Late Cretaceous bonebeds have been uncovered in Western North America that show ceratopsians as gregarious social animals.

Description
Ceratopsians are easily recognized by features of the skull. On the tip of a ceratopsian upper jaw is the rostral bone, a unique bone found nowhere else in the animal kingdom. 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 very tall and flare out sideways, making 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.

History
The first ceratopsian remains known to science were discovered by Fielding Bradford Meek during the U.S. Geological and Geographical Survey of the Territories led by the American geologist F.V. Hayden. In 1872, Meek found several giant bones protruding from a hillside in southwestern Wyoming. He altered palaeontologist Edward 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 species Agathaumas sylvestris, meaning "marvellous forest-dweller."

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 pubis. Marsh considered the group distinct enough to warrant its own suborder within Ornithischia. The name is derived from the Greek κερας/keras meaning 'horn' and οψις/opsis meaning 'face'. As early as the 1960s, it was noted that the name Ceratopsia is actually incorrect linguistically and that it should be Ceratopia. 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 ICZN 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 Ornithischia, though occasionally it has been reduced to the level of infraorder.

Following is a list of ceratopsian genera by classification and location:


 * Infraorder Ceratopsia
 * Yinlong - (Xinjiang, western China)
 * Family Chaoyangsauridae
 * Xuanhuaceratops - (Hebei, China)
 * Chaoyangsaurus - (Liaoning, northeastern China)
 * Family Psittacosauridae
 * Psittacosaurus - (China & Mongolia)
 * Hongshanosaurus - (Liaoning, northeastern China)
 * Clade Neoceratopsia
 * Helioceratops - (Jilin, northwestern China)
 * Yamaceratops - (Mongolia)
 * Auroraceratops - (Gansu, northwestern China)
 * Family Archaeoceratopsidae
 * Archaeoceratops - (Gansu, northwestern China)
 * Liaoceratops - (Liaoning, northeastern China)
 * Family Bagaceratopidae
 * Bagaceratops - (Mongolia)
 * Gobiceratops - (Mongolia)
 * Family Leptoceratopsidae
 * Bainoceratops - (Mongolia)
 * Cerasinops - (Montana, USA)
 * Leptoceratops - (Alberta, Canada & Wyoming, USA)
 * Montanoceratops - (Montana, USA)
 * Prenoceratops - (Montana, USA)
 * Udanoceratops - (Mongolia)
 * Family Protoceratopsidae
 * Graciliceratops - (Mongolia)
 * Bagaceratops - (Mongolia)
 * Breviceratops - (Mongolia)
 * Lamaceratops - (Mongolia)
 * Magnirostris - (Inner Mongolia, China)
 * Platyceratops - (Mongolia)
 * Protoceratops - (Mongolia)
 * Superfamily Ceratopsoidea
 * Zuniceratops - (New Mexico, USA)
 * Family Ceratopsidae

There are several fragmentary Asian forms which may or may not be valid: Asiaceratops, Kulceratops, and Microceratus. 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).

Phylogeny
Paleontologists 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 marginocephalians more closely related to Triceratops than to Pachycephalosaurus. 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 jugals 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 psittacosaurids. Another subset of neoceratopsians is called Coronosauria, which currently includes all ceratopsians more derived than Auroraceratops. Coronosaurs show the first development of the neck frill and the fusion of the first several neck vertebrae 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 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 Leptoceratops. 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 Centrosaurinae and Ceratopsinae (also known as Chasmosaurinae).

Xu/Makovicky/Chinnery Phylogeny:

Xing Xu of the Chinese Institute of Vertebrate Paleontology and Paleoanthropology (IVPP) 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 Liaoceratops. 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 Prenoceratops in 2005 and published a new phylogeny. In 2006, Makovicky and Mark Norell of the AMNH incorporated Chinnery's analysis into their own and also added Yamaceratops, 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. Removal of Asiaceratops stabilizes the entire cladogram.

Makovicky's latest analysis includes IVPP V12722 ("Xuanhuasaurus"), a Late Jurassic ceratopsian from China that at the time was awaiting publication, but has since been published as Xuanhuaceratops. Kulceratops and Turanoceratops are considered nomina dubia in this study. Makovicky believes Lamaceratops, Magnirostris, and Platyceratops to be junior synonyms of Bagaceratops, and Bainoceratops to be synonymous with Protoceratops.

You/Dodson Phylogeny:

You Hailu 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 nomen dubium and not included. Along with Dong Zhiming, You described Magnirostris in 2003, but to date has not included it any of his cladograms.

Biogeography
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 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.

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 ontogenetic variation in these species. Significant sexual dimorphism 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 5/6ths 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.

Diet
While percieved to be herbivores, there is evidence that at least some basal ceratopsians, such as Psittacosaurus were omnivores. All ceratopsians had a large, deep and very often highly recurved beak, somewhat in the manner of a parrot. A beaked non-avian dinosaur is not unusual, but ceratopsian beaks are incredibly deep and robust compared to the flattened, spatulate bill of hadrosaurs or the slender croppers of other beaked dinosaurs. Furthermore, despite the immense side of their heads, ceratopsian bills are tapered, in that they bear little resemblance to the shovel-like mouths of ankylosaurs or hadrosaurs. Ceratopsian beaks seem to indicate that they were capable of producing a decent amount of bite force: certainly the degree of beak curvature produces greater mechanical advantage than a flattened or procumbent beak.

Ceratopsians also posess a unique chewing system. Like other ornithopods, ceratopsians had replaceable, leaf-shaped teeth arranged in batteries. However, chewing ornithopods have pleurokinetic skulls – that is, the cheek region of the upper jaw can bulge ever so slightly when the lower jaw is adducted, meaning the food between their teeth is ground and torn laterally as they masticate. By contrast, ceratopsian jaws are not pleurokinetic and can only operate in the vertical plane. In fact, the tooth wear on ceratopsian teeth shows that the teeth occluded exactly in this manner. Because their cheek region is absolutely stuffed solid with teeth, their dentition essentially acts like a set of shears, chopping foodstuffs rather than grinding it.

The bone surface texture of ceratopsian frills doesn’t show features you’d expect from muscle anchorage and, besides, most of these frills have dirty-big holes in them: you can’t anchor big jaw adductor muscles to nothing but soft-tissue. However, this does not mean the real regions of jaw muscle attachment are anything to be sneezed at: rather, ceratopsians have large, robust coronoid processes (that is, an upright extension of bone on the lower jaw) that would allow for anchorage of big external adductor muscles. Conversely, the sites for anchoring the internal adductor musculature aren’t huge (except for in some basal forms), but the jaw joint certainly is: it’s like the sort of hinge you’d see on a drawbridge. Such a structure would not be needed if ceratopsians had weak, flimsy bites. Further physical breakdown of foodstuffs would take place in a stone-filled gizzard, as known in Psittacosaurus.

Based upon the nature of their jaws and beaks, it is determined that they were selective feeders: their beaks are far too narrow to harvest food en masse. From the large size of the gut cavities in these animals, it does appear that vegetative matter of some kind made up a reasonable percentage of their diet.

Posture and locomotion
Most restorations of ceratopsians show them with erect hindlimbs but semi-sprawling forelimbs, which suggest 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.

Discovery
The first remains of Dorygnathus, which consisted of isolated bones and jaw fragments, were discovered in the Toarcian-age Posidonia Shale, near Banz, Bavaria. In 1830, they were described by Carl Theodori as Ornithocephalus banthensis, the specific name referring to Banz. The holotype specimen, a lower jaw, is cataloged as PSB 757. The fossils were studied by Christian Erich Hermann von Meyer in 1831 and again by Theodori in 1852 when he referred them to the genus Rhamphorhynchus. During this time, it was assumed that a British pterosaur, later named Dimorphodon, shared several characteristics with Dorygnathus. Some fossils were sent to a professor of palaeontology in Munich named Johann Andreas Wagner. It was he who, having studied new finds by Alfred Oppel in 1856 and 1858, after Richard Owen had named Dimorphodon concluded that the German type was clearly different and that therefore a new genus of pterosaur should be erected, which he formally named Dorygnathus in 1860, from Greek dory, "spear" and gnathos, "jaw". Much more complete remains have been found since in other German locales and especially in Württemberg, including Holzmaden, Ohmden, and Zell. One specimen, SMNS 81840, has in 1978 been dug up in Nancy, France. Dorygnathus fossils were often found in the spoil heaps where unusable rock was dumped from slate quarries worked by local farmers. Most fossils were found in two major waves, one during the twenties, the other during the eighties of the twentieth century. Since then the rate of discovery has slowed considerably because the demand for slate has strongly diminished and many small quarries have closed. At present over fifty specimens have been collected, many of them are preserved in the collection of the State Museum of Natural History Stuttgart, as by law paleontological finds in Baden-Württemberg are property of this Bundesland. Due to the excellent preserval of the later found fossils, Dorygnathus has generated much interest by pterosaur researchers, important studies having been dedicated to the species by Felix Plieninger, Gustav von Arthaber, and more recently Kevin Padian.

Description
Dorygnathus in general has the build of a basal, i.e. non-pterodactyloid pterosaur: a short neck, a long tail and short metacarpals — although for a basal pterosaur the neck and metacarpals of Dorygnathus are again relatively long. The skull is elongated and pointed. The largest known cranium, that of specimen MBR 1920.16 prepared by Bernard Hauff in 1915 and eventually acquired by the Natural History Museum of Berlin, has a length of sixteen centimetres. In the skull the eye socket forms the largest opening, larger than the fenestra antorbitalis that is clearly separated from the slit-like bony naris. No bony crest is visible on the rather straight top of the skull or snout. The lower jaws are thin at the back but deeper toward the front where they fuse into the symphysis ending in a toothless point after which the genus has been named. In MBR 1920.16, the mandibula as a whole has a length of 147 millimetres.

In the lower jaws the first three pairs of teeth are very long, sharp and pointing outwards and forwards. They contrast with a row of eight or more upright-standing much smaller teeth that gradually diminish in size towards the back of the lower jaw. No such extreme contrast exists in the upper jaws, but the four teeth in the premaxilla are longer than the seven in the maxilla that again become smaller posteriorly. The total number of teeth is thus at least 44. The long upper and lower front teeth interlaced when the beak was closed; due to their extreme length they then projected considerably beyond the upper and lower margins of the head.

According to Padian, eight cervical, fourteen dorsal, three or four sacral and twenty-seven or twenty-eight caudal vertebrae are present. The exceptional fourth sacral is the first of the normal caudal series. The number of caudals is not certain because their limits are obscured by long thread-like extensions, stiffening the tail. The cervical vertebrae are rather long and strongly built, their upper surface having a roughly square cross-section. They carry double-headed thin cervical ribs. The dorsal vertebrae are more rounded with flat spines; the first three or four carry ribs that contact the sternal ribs; the more posterior ribs contact the gastralia. The first five or six, rather short, caudal vertebrae form a flexible tail base. To the back the caudals grow longer and are immobilised by their intertwining extensions with a length of up to five vertebrae which together surround the caudals with a bony network, allowing the tail to function as a rudder.

The breastbone is triangular and relatively small; Padian has suggested it may have been extended at its back with a cartilaginous tissue. It is connected to the coracoid which in older individuals is fused to the longer scapula forming a saddle-shaped shoulder joint. The humerus has a triangular deltopectoral crest and is pneumatised. The lower arm is 60% longer than the upper arm. From the five carpal bones in the wrist a short but robust pteroid points towards the neck, in the living animal a support for a flight membrane, the propatagium. The first three metacarpals are connected to three small fingers, equipped with short but strongly curved claws; the fourth to the wing finger, in which the second or third phalanx is the longest; the first or fourth the shortest. The wing finger supports the main flight membrane.

In the pelvis, the ilium, ischium and pubis are fused. The ilium is elongated with a length of six vertebrae. The lower leg, in which the lower two thirds of the tibia and fibula of adult specimens are fused, is a third shorter than the thighbone, the head of which makes an angle of 45° with its shaft. The proximal tarsals are never fused in a separate astragalocalcaneum; a tibiotarsus is formed. The third metatarsal is the longest; the fifth is connected to a toe of which the second phalanx shows a 45° bend and has a blunt and broad end; it perhaps supported a membrane between the legs, a cruropatagium.

In some specimens, soft parts have been preserved but these are rare and limited, providing little information. It is unknown whether the tail featured a vane on its end, as with Rhamphorhynchus. However, Ferdinand Broili reported the presence of hairs in specimen BSP 1938 I 49, an indication that Dorygnathus also had fur and an elevated metabolism, as is presently assumed for all pterosaurs.

Dorygnathus mistelgauensis
In 1971 Rupert Wild described and named a second species: Dorygnathus mistelgauensis, based on a specimen collected in a brick pit near the railway station of Mistelgau, to which the specific name refers, by teacher H. Herppich, who donated it to the private collection of Günther Eicken, a local amateur paleontologist at Bayreuth, where it still resides. As a result the exemplar has no official inventory number. The fossil comprises a shoulder-blade with wing, a partial leg, a rib and a caudal vertebra. Wild justified the creation of a new species name by referring to the great size, with an about 50% larger wingspan than with a typical specimen; the short lower leg and the long wing.

Padian in 2008 pointed out that D. banthensis specimen MBR 1977.21, the largest then known, has with a wingspan of 169 centimetres an even larger size; that wing and lower leg proportions are rather variable in D. banthensis and that the geological age is comparable. He concluded that D. mistelgauensis is a subjective junior synonym of D. banthensis.

Phylogeny
The affinity between Dorygnathus and Dimorphodon, assumed by early researchers, was largely based on a superficial resemblance in tooth form. Baron Franz Nopcsa in 1928 assigned the species to the Rhamphorhynchinae, which was confirmed by Peter Wellnhofer in 1978. Modern exact cladistic analyses of the relationships of Dorygnathus have not resulted in a consensus. David Unwin in 2003 found that it belonged to the clade Rhamphorhynchinae, but analyses by Alexander Kellner resulted in a much more basal position, below Dimorphodon or Peteinosaurus. Padian, using a comparative method, in 2008 concluded that Dorygnathus was close to Scaphognathus and Rhamphorhynchus in the phylogenetic tree but also that these species were forming a series of successive off-shoots, meaning that they would not be united in a separate clade. This was again contradicted by the results of a cladistic study by Brian Andres in 2010 showing that Dorygnathus was part of a monophyletic Rhamphorhynchinae. The following cladogram shows the position of Dorygnathus according to Andres:

Palaeobiology
Dorygnathus is commonly thought to have had a piscivorous way of living, catching fish or other slippery sea-creatures with its long teeth. This is confirmed by the fact that the fossils have been found in marine sediments, deposited in the seas of the European Archipelago. In these it is present together with the pterosaur Campylognathoides that however is much more rare. Very young juveniles of Dorygnathus are unknown, the smallest discovered specimen having a wingspan of sixty centimetres; perhaps they were unable to venture far over open sea. Padian concluded that Dorygnathus after a relatively fast growth in its early years, faster than any modern reptile of the same size, kept slowly growing after having reached sexual maturity, which would have resulted in exceptionally large individuals with a 1.7 metres wingspan.

On land, Dorygnathus was probably not a good climber; its claws show no special adaptations for this type of locomotion. According to Padian, Dorygnathus, as a small pterosaur with a long tail, was well capable of bipedal movement, though its long metacarpals would make him better suited for a quadrupedal walk than most basal pterosaurs. Most researchers however, today assume quadrupedality for all pterosaurs.