1. Centrosaurus apertus 2. Chasmosaurus belli 3. Torosaurus latus 4. Triceratops horridus
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.
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 ("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.