Ceratopsians (Ceratopsia)

Ceratopsians were ornithischians, or "bird-hipped" dinosaurs. The oldest ceratopsians appeared at the beginning of the Cretaceous, about 140 million years ago. In the Late Cretaceous, about 100 million years ago, the ceratopsians began to diversify in North America and in Asia. Forms without the enormous horns and frills of Triceratops, in the family Protoceratopsidae, include the Mongolian genus Protoceratops and the unusual bipedal, frill-less dinosaur Psittacosaurus ("parrot-lizard"). The horned, frilled dinosaurs in the family Ceratopsidae are found only in the Late Cretaceous of  North America; they are among the last of the dinosaurs (other than the birds of course).

Ceratopsians 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.
How did ceratopsians live? Their "beak" and rows of grinding cheek teeth suggest that they fed on tough vegetation. The huge, heavy "frill" of ceratopsians such as Triceratops may have served as armor against the attacks of saurischian predators like Tyrannosaurus, which lived in the same time and place as Triceratops. However, other ceratopsians had smaller frills and/or frills with large openings; such frills would have been little defense against a predator. So ceratopsian frills may also have functioned as heat radiators, or signaling devices, or to attract mates, in addition to whatever protective function they may or may not have had. Recent work on the oxygen isotopes found inside the bony frill, which indicate the relative temperatures of different parts of the bone, supports the first of these hypotheses: the frills functioned as heat radiators.

1. Centrosaurus apertus 2. Chasmosaurus belli 3. Torosaurus latus 4. Triceratops horridus
Ceratopsians probably traveled in herds; there are "bone beds" in the western United States that contain the bones of hundreds of individuals of the same species of ceratopsian. If attacked, the herd could stampede, or "circle the wagons" and fend off predators. In terms of animals living today, it may be best to think of ceratopsians — at least the larger ones — as analogues of elephants or rhinos: large herbivores in herds that relied on horns and attitude to protect themselves.
The Ceratopsians and pachycephalosaurs ("bone-heads") together make up the Marginocephalia.

The largest ceratopsian known is Eotriceratops


Eotriceratops (meaning "dawn three-horned face") is a genus of herbivorous ceratopsian dinosaurs which lived in the area of North America during the late Cretaceous period. The only named species is Eotriceratops xerinsularis.
In early August 1910, Barnum Brown during an American Museum of Natural History expedition discovered a large dinosaur skeleton in the Dry Island site, on the west bank of the Red Deer River in southern Alberta, Canada. Brown however, neglected this find as he was more interested in the many Albertosaurus specimens present in the location. Unaware of Brown"s prospect, in 2001 a team of the Royal Tyrrell Museum of Palaeontology and the Canadian Museum of Nature mounted an expedition to the Dry Island. The expedition"s cook, Glen Guthrie, that year by accident rediscovered the skeleton.
The holotype specimen, RTMP 2002.57.5, has been found in a layer of the uppermost Horseshoe Canyon Formation, dated to the early Maastrichtian, about 67.6 million years ago. It consist of a partial skeleton with skull, lacking the lower jaws. It contains a partial skull including parts of the frill sides, large horns above the eyes, and a small horn above the nose, similar to the closely related Triceratops. At least seven neck and five back vertebrae, as well as several ribs and ossified tendons, were also recovered. The bones were largely found disarticulated. Because the specimen was found in weakly bedded shale, many of the bones were badly crushed.
In 2010, Gregory S. Paul renamed the species to Triceratops xerinsularis but this was not followed by other researchers.
Possible additional specimens, which have been variously classified in the species Ojoceratops fowleri and Torosaurus utahensis, are known from the same time period in New Mexico and may also belong to Eotriceratops.
The holotype skull has been estimated to have had an original length of around 3 m (9.8 ft).It has been estimated that this specimen had a total length of about 12 m (37 ft).In 2010, Paul estimated its length at 10 metres, its weight at 13 tonnes. Eotriceratops differs from other chasmosaurine ceratopsians in unique features of the skull bones. In 2007, several autapomorphies, unique derived traits, were established. The process of the praemaxilla, obliquely protruding to above and behind in the bony nostril, does not have a groove or depression on its outer side contrary to the situation with Triceratops; this process is exceptionally wide in side view; it also reaches above the level of the lower border of the fenestra interpraemaxillaris. The episquamosals, the epoccipitals of the squamosal, thus the skin ossifications lining and often protruding from the edge of the frill, have an extremely elongated base, and are flattened and spindly, touching each other as with Torosaurus utahensis. Near the lower edge of the squamosal a clearly demarcated groove or depression is present. On the lower front of the nasal horn core, a vertical, slightly obliquely running, vein groove meets second vein groove, running horizontally. The epijugal forms an unusually pronounced sharp jugal horn. At its rear upper side the epijugal bears a pronounced process, pointing to behind. A depression on the top of the epijugal forms a contact facet with the jugal; a depression at its inner side forms a separate facet contacting the quadratojugal.
The snout of Eotriceratops was relatively flat and elongated. The depressions on the sides of the praemaxillae were connected through an oval fenestra interpraemaxillaris; small rounded processes pointed to above and behind into this opening, originating from the front lower edges. The strut between this opening and the nostril was narrow in side view and transversely thickened with a straight rear edge. The processes jutting into the nostrils had hollow outer sides but were far less excavated and much higher than with Triceratops or Torosaurus.The maxilla bore at least thirty-five tooth positions. The nasal horn was low, situated above the nostril and slightly recurved. It had a narrow rear edge and a transversely flattened point. The horns above the eyes were forward-curving and have been estimated at about 80 centimetres (2.6 ft) long. The lower base of these horns was narrow and vertically directed, which with Triceratops is a juvenile trait. Three bite marks can be observed above the eye, near the base of the left horn, which were interpreted as traces of scavenging. The squamosal shows at least five episquamosals. Little has been preserved of the parietal bones forming the centre of the neck shield.

Triceratops

For most people this is ‘the’ ceratopsian dinosaur of choice, and the one that is by far the most popular of them all. Triceratops had three large horns (hence the name Triceratops which means ‘three horned face’), a robust neck frill, and a larger than average size, all things that have confirmed its place in popular culture. Triceratops has often been shown in opposition against large predatory dinosaurs such as tyrannosaurs, usually charging at them like a rhino. However the skull of Triceratops has been proven to be incapable of withstanding the stresses that impacts from charging would inflict. Also while there is fossil evidence that shows tyrannosaur tooth marks on Triceratops fossils, no tyrannosaurs have been proven to have been hurt by Triceratops. With that said, tyrannosaurs did have other kinds of dinosaurs to target such as hadrosaurs that would have been far easier prey than ceratopsians. Some Triceratops crests show damage that some palaeontologists have interpreted as being caused by the horns of other Triceratops. It has been considered that rather than charging at predators, Triceratops may have used their horns on each other in duelling contests in order to assert dominance over rivals that could not be intimidated by just a visual display.
Triceratops would have lived alongside other types of ceratopsian dinosaurs, though not the previously mentioned Styracosaurus as it is often depicted since this genus lived much earlier in Campanian stage of the Cretaceous, whereas Triceratops is late Maastrichtian. In 2010 it was claimed that another genus of ceratopsian named Torosaurus was not only a synonym to Triceratops, but actually represented the true adult form. Torosaurus is noted for having a very similar body and horn arrangement to Triceratops, but a much larger neck frill with openings, whereas the frill on known Triceratops is relatively short and solid. Others have not been convinced however noting that a lack of known Torosaurus individuals at different ages makes a comparison to Triceratops difficult to establish. Differences in the skulls of Triceratops and Torosaurus are also pointed out, as well as to date there is no known occurrence of holes appearing in frills of adult ceratopsians when subadults and even juveniles do not have them (holes in the frill usually start developing very early on in life). Either Triceratops and Torosaurus are indeed separate, or Triceratops would be the first known ceratopsian where frill holes suddenly appear upon adulthood.

Titanoceratops (Titan horned face)

Initially thought to represent a large Pentaceratops individual, Titanoceratops was declared its own genera after further study found the material to belong to a new, although still very similar, ceratopsian dinosaur. The large size of Titanoceratops was the inspiration for the new genera name, with the species name T. ouranos derived from the Titan Ouranos, who in Greek mythology was the first ruler of the Titans.
The skull measures 1.2 m (3.9 ft) from the tip of the snout to the quadrate and its restored frill extends its total length up to 2.65 m (8.7 ft) making it a candidate for the longest skull of any terrestrial vertebrate. Titanoceratops was as large as the later triceratopsins with an estimated weight of 6.55 tonnes (7.22 short tons) and a mounted skeleton measuring 6.8 metres (22 ft) long and 2.5 metres (8.2 ft) tall at the back. Tom Holtz (2012) noted that it is extremely similar to its closely related contemporaries Eotriceratops and Ojoceratops, which may all be synonymous. The holotype skeleton of Titanoceratops consists of a partial skull with jaws, syncervical, cervical, dorsal, and sacral vertebrae, caudal certebrae, ribs, humeri, a right radius, femora, tibiae, a right fibula, both ilia, both ischia, and ossified tendons. In total, the amount of material assigned to Titanoceratops means it is quite well known, along with genera like Triceratops, Vagaceratops, Pentaceratops, Chasmosaurus, Centrosaurus, Styracosaurus, and Anchiceratops.

Torosaurus latus

Torosaurus ("perforated lizard", in reference to the large openings in its frill) is a genus of herbivorous ceratopsid dinosaur that lived during the late Maastrichtian stage of the Cretaceous period, between 68 and 66 million years ago. Fossils have been discovered across the Western Interior of North America, from Saskatchewan to southern Texas.
Torosaurus possessed one of the largest skulls of any known land animal. The frilled skull reached up to 2.77 metres (9.1 ft) in length. From head to tail, Torosaurus is thought to have measured about 7.6 to 9 m (25 to 30 ft) long and weighed four to six tonnes. Torosaurus is distinguished from the contemporary Triceratops by an elongate frill with large openings (fenestrae), long squamosal bones of the frill with a trough on their upper surface, and the presence of five or more pairs of hornlets (epoccipitals) on the back of the frill.Torosaurus also lacked the long nose horn seen in Triceratops prorsus, and instead resembled the earlier and more basal Triceratops horridus in having a short nose horn. Three species have been named, Torosaurus latus, T. gladius and T. utahensis. T. gladius is no longer considered a valid species, however.

Pachycephalosaurids

1. Prenocephale 2. Homalocephale 3. Pachycephalosaurus 4. Stegoceras 5. Stygimoloch
Pachycephalosaurs, also known colloquially as "bone heads", were small to medium sized herbivores who lived during the Mid to Late Cretaceous. With the exception of two species, most pachycephalosaurs lived during the Late Cretaceous Period, dating between about 85.8 and 65.5 million years ago. Pachycephalosaurs lived exclusively in Laurasia, being found in western North America and central Asia. Pachycephalosaurs originated in Asia and had two major dispersal events, resulting in the two separate waves of pachycephalosaur evolution observed in Asia. The first, occurring before the late Santonian or early Campanian, involved a migration from Asia to North America, most likely by way of the Bering Land Bridge. This migration was by a common ancestor of Stygimoloch, Stegoceras, Tylocephale, Prenocephale, and Pachycephalosaurus. The second event occurred before the middle Campanian, and involved a migration back into Asia from North America by a common ancestor of Prenocephale and Tylocephale.Two species originally reported to be pachycephalosaurs discovered outside this range, Yaverlandia bitholus of England and Majungatholus atopus of Madagascar, have recently been shown to actually be theropods.
Candidates for the earliest known pachycephalosaur include Ferganocephale adenticulatum from Middle Jurassic Period strata of Kyrgyzstan and Stenopelix valdensis from Early Cretaceous strata of Germany, although R.M. Sullivan has doubted that either of these species are pachycephalosaurs.In 2017, a phylogenetic analysis conducted by Han and colleagues identified Stenopelix as a member of the Ceratopsia.

Some researchers insist that the domed skulls of pachycephalosaurs, which in some cases are eight inches thick, were made from brittle bone, and those with particularly high and curved domes would require the precision of a surgeon to pull off anything more than a glancing blow. Also, despite being quite stocky and well made, their head, neck and spine could not be aligned in such a way to transmit stress, unlike modern day Musk Ox. So perhaps, instead, they participated in bouts of flank-butting which would inflict pain-a-plenty on whatever was on the receiving end, especially when you consider the lumps and horns that adorn some domes.
The opposition researchers, well, they are all for head banging. As well as a unique "wall" of bone on the inside of the eye socket to perhaps secure the eyeball and protect it from contact-shock during ramming contests, around 22% of 100 pachycephalosaur skulls that were scrutinized as part of a 2013 study sported damage that had previously been brushed off as artifacts of preservation, but which were consistent with osteomyelitis; an infection of the bone resulting from penetrating trauma, or trauma to the tissue overlying the skull leading to an infection of the bone tissue. Unless consistent external factors were at work, it seems likely that these surface wounds, which had healed as well as could be, were incurred during bouts of head-to-head combat. Flat-headed specimens, which are probably all juveniles, were damage free.
Of course, whether pachycephalosaurs were head bangers or not we"ll never know for sure, but we"re willing to bet that males with the biggest domes were more popular with females than those with smaller ones.

Pachycephalosaurus

Pachycephalosaurus is the last, largest, and most famous member of the Pachycephalosauria, or thick-headed dinosaurs. In the 1970s paleontologist Peter Galton proposed that male pachycephalosaurs used their dome heads as battering rams, like Bighorn sheep. The idea caught the public"s imagination, and two individuals are seen doing this in The Lost World: Jurassic Park. But by the 1990s, scientists began to question Galton"s head butting theory. It was pointed out that animals who do butt heads have a wide surface area where the heads come into contact to prevent "head slippage." This happens when two animals butt heads at high speed and do not hit straight on. The risk breaking their necks when their heads suddenly snap to one side. Pachycephalosaurus has a domed, or rounded, head, which would minimize surface contact and therefore increase the risk of head slippage. This throws doubt on the idea of any high speed head-butting between pachycephalosaurs, but it does not exclude "head-pushing" of "head-ramming" against non-pachycephalosaurs.
Pachycephalosaurus is famous for having a large, bony dome atop its skull, up to 25 cm (10 in) thick, which safely cushioned its tiny brain. The dome"s rear aspect was edged with bony knobs and short bony spikes projected upwards from the snout. The spikes were probably blunt, not sharp.

The skull was short, and possessed large, rounded eye sockets that faced forward, suggesting that the animal had good eyesight and was capable of binocular vision. Pachycephalosaurus had a small muzzle which ended in a pointed beak. The teeth were tiny, with leaf-shaped crowns. The head was supported by an "S"- or "U"-shaped neck.Younger individuals of Pachycephalosaurus maybe have had flatter skulls, with larger horns projecting from the back of the skull. As the animal grew, the horns shrunk and rounded out, as the dome grew.
Pachycephalosaurus was probably bipedal and was the largest of the pachycephalosaurid (bone-headed) dinosaurs. It has been estimated that Pachycephalosaurus was about 5.5 metres (18 ft) long and weighed about 550 kilograms (1200 lb).Based on other pachycephalosaurids, it probably had a fairly short, thick neck, short fore limbs, a bulky body, long hind legs and a heavy tail, which was likely held rigid by ossified tendons.
Pachycephalosaurus possibly co-existed alongside additional pachycephalosaur species of the genera Sphaerotholus, as well as Dracorex and Stygimoloch, though these last two genera may represent juveniles of Pachycephalosaurus itself.Other dinosaurs that shared its time and place include Thescelosaurus, the hadrosaurid Edmontosaurus and a possible species of Parasaurolophus, ceratopsids like Triceratops, Torosaurus, Nedoceratops, Tatankaceratops and Leptoceratops, ankylosaurids Ankylosaurus, nodosaurids Denversaurus and Edmontonia, and the theropods Acheroraptor, Dakotaraptor, Ornithomimus, Struthiomimus, Anzu, Leptorhynchos, Troodon, Pectinodon, Paronychodon, Richardoestesia and Tyrannosaurus.