Triceratops
Triceratops | |
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Skeletal mount of a T. prorsus specimen at the Natural History Museum of Los Angeles | |
Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Chordata |
Clade: | Dinosauria |
Clade: | †Ornithischia |
Clade: | †Ceratopsia |
Family: | †Ceratopsidae |
Subfamily: | †Chasmosaurinae |
Tribe: | †Triceratopsini |
Genus: | †Triceratops Marsh, 1889b |
Type species | |
†Ceratops horridus Marsh, 1889a
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Species | |
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Synonyms | |
List
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Triceratops () meaning 'face'.
Bearing a large bony
Triceratops was traditionally placed within the "short-frilled" ceratopsids, but modern
Triceratops has been documented by numerous remains collected since the genus was first described in 1889 by American paleontologist
Discovery and identification
The first named
Although not confidentially assignable, fossils possibly belonging to Triceratops were described as two taxa, Agathaumas sylvestris and Polyonax mortuarius, in 1872 and 1874, respectively, by Marsh's archrival Edward Drinker Cope.[6][7] Agathaumas was named based on a pelvis, several vertebrae, and a few ribs collected by Fielding Bradford Meek and Henry Martyn Bannister near the Green River of southeastern Wyoming from layers coming from the Maastrichtian Lance Formation.[8] Due to the fragmentary nature of the remains, it can only confidently be assigned to Ceratopsidae.[9][10] Polyonax mortuarius was collected by Cope himself in 1873 from northeastern Colorado, possibly coming from the Maastrichtian Denver Formation.[11][7] The fossils only consisted of fragmentary horn cores, 3 dorsal vertebrae, and fragmentary limb elements.[7] Polyonax has the same issue as Agathaumas, with the fragmentary remains non-assignable beyond Ceratopsidae.[12][9]
The Triceratops holotype, YPM 1820, was collected in 1888 from the Lance Formation of Wyoming by fossil hunter John Bell Hatcher, but Marsh initially described this specimen as another species of Ceratops.[13] Cowboy Edmund B. Wilson had been startled by the sight of a monstrous skull poking out of the side of a ravine. He tried to recover it by throwing a lasso around one of the horns. When it broke off, the skull tumbling to the bottom of the cleft, Wilson brought the horn to his boss. His boss was rancher and avid fossil collector Charles Arthur Guernsey, who just so happened to show it to Hatcher. Marsh subsequently ordered Hatcher to locate and salvage the skull.[9] The holotype was first named Ceratops horridus. When further preparation uncovered the third nose horn, Marsh changed his mind and gave the piece the new generic name Triceratops (lit. 'three horn face'), accepting his Bison alticornis as another species of Ceratops.[14] It would, however, later be added to Triceratops.[15] The sturdy nature of the animal's skull has ensured that many examples have been preserved as fossils, allowing variations between species and individuals to be studied. Triceratops remains have subsequently been found in Montana and South Dakota (and more in Colorado and Wyoming), as well as the Canadian provinces of Saskatchewan and Alberta.
Species
After Triceratops was described, between 1889 and 1891, Hatcher collected another thirty-one of its skulls with great effort. The first species had been named T. horridus by Marsh. Its specific name was derived from the Latin word horridus meaning "rough" or "rugose", perhaps referring to the type specimen's rough texture, later identified as an aged individual. The additional skulls varied to a lesser or greater degree from the original holotype. This variation is unsurprising, given that Triceratops skulls are large three-dimensional objects from individuals of different ages and both sexes that which were subjected to different amounts and directions of pressure during fossilization.[9]
In the first attempt to understand the many species, Richard Swann Lull found two groups, although he did not say how he distinguished them. One group composed of T. horridus, T. prorsus, and T. brevicornus ('the short-horned'). The other composed of T. elatus and T. calicornis. Two species (T. serratus and T. flabellatus) stood apart from these groups.[15] By 1933, alongside his revision of the landmark 1907 Hatcher–Marsh–Lull monograph of all known ceratopsians, he retained his two groups and two unaffiliated species, with a third lineage of T. obtusus and T. hatcheri ('Hatcher's') that was characterized by a very small nasal horn.[10] T. horridus–T. prorsus–T. brevicornus was now thought to be the most conservative lineage, with an increase in skull size and a decrease in nasal horn size. T. elatus–T. calicornis was defined by having large brow horns and small nasal horns.[10][16] Charles Mortram Sternberg made one modification by adding T. eurycephalus ('the wide-headed') and suggesting that it linked the second and third lineages closer together than they were to the T. horridus lineage.[17]
With time, the idea that the differing skulls might be representative of individual variation within one (or two) species gained popularity. In 1986, John Ostrom and Peter Wellnhofer published a paper in which they proposed that there was only one species, Triceratops horridus.[18] Part of their rationale was that there are generally only one or two species of any large animal in a region. To their findings, Thomas Lehman added the old Lull–Sternberg lineages combined with maturity and sexual dimorphism, suggesting that the T. horridus–T. prorsus–T. brevicornus lineage was composed of females, the T. calicornis–T. elatus lineage was made up of males, and the T. obtusus–T. hatcheri lineage was of pathologic old males.[19]
These findings were contested a few years later by paleontologist Catherine Forster, who reanalyzed Triceratops material more comprehensively and concluded that the remains fell into two species, T. horridus and T. prorsus, although the distinctive skull of T. ("Nedoceratops") hatcheri differed enough to warrant a separate genus.[20] She found that T. horridus and several other species belonged together and that T. prorsus and T. brevicornus stood alone. Since there were many more specimens in the first group, she suggested that this meant the two groups were two species. It is still possible to interpret the differences as representing a single species with sexual dimorphism.[9][21]
In 2009, John Scannella and Denver Fowler supported the separation of T. prorsus and T. horridus, noting that the two species are also separated stratigraphically within the Hell Creek Formation, indicating that they did not live together at the same time.[22]
Valid species
- T. horridus (Marsh, 1889) Marsh, 1889 (originally Ceratops) (type species)
- T. prorsus Marsh, 1890
Synonyms and doubtful species
Some of the following species are synonyms, as indicated in parentheses ("=T. horridus" or "=T. prorsus"). All the others are each considered a nomen dubium (lit. 'dubious name') because they are based on remains too poor or incomplete to be distinguished from pre-existing Triceratops species.
- T. albertensis C. M. Sternberg, 1949
- T. alticornis (Marsh 1887) Hatcher, Marsh, and Lull, 1907 [originally Bison alticornis, Marsh 1887, and Ceratops alticornis, Marsh 1888]
- T. brevicornus Hatcher, 1905 (=T. prorsus)
- T. calicornis Marsh, 1898 (=T. horridus)
- T. elatus Marsh, 1891 (=T. horridus)
- T. eurycephalus Schlaikjer, 1935
- T. flabellatus Marsh, 1889 (= Sterrholophus Marsh, 1891) (=T. horridus)
- T. galeus Marsh, 1889
- T. hatcheri (Hatcher & Lull 1905) Lull, 1933 (contentious; see Nedoceratops below)
- T. ingens Marsh vide Lull, 1915
- T. maximus Brown, 1933
- T. mortuarius (Polyonax mortuarius)
- T. obtusus Marsh, 1898 (=T. horridus)
- T. serratus Marsh, 1890 (=T. horridus)
- T. sulcatus Marsh, 1890
- T. sylvestris (Cope, 1872) Kuhn, 1936 (Agathaumas sylvestris)
Description
Size
Triceratops was a very large animal, reaching 8–9 metres (26–30 ft) in length and weighing 5–9 metric tons (5.5–9.9 short tons).
Skull
Like all chasmosaurines, Triceratops had a large skull relative to its body size, among the largest of all land animals. The largest-known skull, specimen MWC 7584 (formerly BYU 12183), is estimated to have been 2.5 meters (8.2 ft) in length when complete[29] and could reach almost a third of the length of the entire animal.[30]
The front of the head was equipped with a large beak in front of its teeth. The core of the top beak was formed by a special rostral bone. Behind it, the premaxillae bones were located, embayed from behind by very large, circular nostrils. In chasmosaurines, the premaxillae met on their midline in a complex bone plate, the rear edge of which was reinforced by the "narial strut". From the base of this strut, a triangular process jutted out into the nostril. Triceratops differs from most relatives in that this process was hollowed out on the outer side. Behind the toothless premaxilla, the maxilla bore thirty-six to forty tooth positions, in which three to five teeth per position were vertically stacked. The teeth were closely appressed, forming a "dental battery" curving to the inside. The skull bore a single horn on the snout above the nostrils. In Triceratops, the nose horn is sometimes recognisable as a separate ossification, the epinasal.[31]
The skull also featured a pair of supraorbital "brow" horns approximately 1 meter (3.3 ft) long, with one above each eye.[32][33] The jugal bones pointed downward at the rear sides of the skull and were capped by separate epijugals. With Triceratops, these were not particularly large and sometimes touched the quadratojugals. The bones of the skull roof were fused and by a folding of the frontal bones, a "double" skull roof was created. In Triceratops, some specimens show a fontanelle, an opening in the upper roof layer. The cavity between the layers invaded the bone cores of the brow horns.[31]
At the rear of the skull, the outer
The lower jaws were elongated and met at their tips in a shared epidentary bone, the core of the toothless lower beak. In the dentary bone, the tooth battery curved to the outside to meet the battery of the upper jaw. At the rear of the lower jaw, the articular bone was exceptionally wide, matching the general width of the jaw joint.[31] T. horridus can be distinguished from T. prorsus by having a shallower snout.[25]
Postcranial skeleton
Chasmosaurines showed little variation in their postcranial skeleton.[31] The skeleton of Triceratops is markedly robust. Both Triceratops species possessed a very sturdy build, with strong limbs, short hands with three hooves each, and short feet with four hooves each.[35] The vertebral column consisted of ten neck, twelve back, ten sacral, and about forty-five tail vertebrae. The front neck vertebrae were fused into a syncervical. Traditionally, this was assumed to have incorporated the first three vertebrae, thus implying that the frontmost atlas was very large and sported a neural spine. Later interpretations revived an old hypothesis by John Bell Hatcher that, at the very front, a vestige of the real atlas can be observed, the syncervical then consisting of four vertebrae. The vertebral count mentioned is adjusted to this view. In Triceratops, the neural spines of the neck are constant in height and don't gradually slope upwards. Another peculiarity is that the neck ribs only begin to lengthen with the ninth cervical vertebra.[31]
The rather short and high vertebrae of the back were, in its middle region, reinforced by ossified tendons running along the tops of the
Although certainly
The hands and forearms of Triceratops retained a fairly primitive structure when compared to other quadrupedal dinosaurs, such as
Skin
Preserved skin from Triceratops is known. This skin consist of large scales, some of which exceed 100 millimetres (3.9 in) across, which have conical projections rising from their center. A preserved piece of skin from the frill of a specimen is also known, which consists of small polygonal basement scales.[40]
Classification
Triceratops is the best-known genus of
In 1949, Charles Mortram Sternberg was the first to question this position, proposing instead that Triceratops was more closely related to Arrhinoceratops and Chasmosaurus based on skull and horn features, making Triceratops a chasmosaurine ("ceratopsine" in his usage) genus.[17] He was largely ignored, with John Ostrom[43] and later David Norman placing Triceratops within the Centrosaurinae.[44]
Subsequent discoveries and analyses, however, proved the correctness of Sternberg's view on the position of Triceratops, with Thomas Lehman defining both subfamilies in 1990 and diagnosing Triceratops as "ceratopsine" on the basis of several morphological features. Apart from the one feature of a shortened frill, Triceratops shares no derived traits with centrosaurines.
The cladogram below follows Longrich (2014), who named a new species of Pentaceratops, and included nearly all species of chasmosaurine.[47]
Chasmosaurinae |
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For many years after its discovery, the deeper evolutionary origins of Triceratops and its close relatives remained largely obscure. In 1922, the newly discovered Protoceratops was seen as its ancestor by Henry Fairfield Osborn,[9] but many decades passed before additional findings came to light. Recent years have been fruitful for the discovery of several antecedents of Triceratops. Zuniceratops, the earliest-known ceratopsian with brow horns, was described in the late 1990s, and Yinlong, the first known Jurassic ceratopsian, was described in 2005.
These new finds have been vital in illustrating the origins of ceratopsians in general, suggesting an Asian origin in the Jurassic and the appearance of truly horned ceratopsians by the beginning of the Late Cretaceous in North America.[31]
In
Paleobiology
Although Triceratops is commonly portrayed as a
For many years, Triceratops finds were known only from solitary individuals.
Analysis of the endocranial anatomy of Triceratops suggest its sense of smell was poor compared to that of other dinosaurs. Its ears were attuned to low frequency sounds, given the short cochlear lengths recorded in an analysis by Sakagami et al,. This same study also suggests that Triceratops held its head about 45 degrees to the ground, an angle which would showcase the horns and frill most effectively that simultaneously allowed the animal to take advantage of food through grazing.[57]
A 2022 study by Wiemann and colleagues of various dinosaur genera, including Triceratops, suggests that it had an
Dentition and diet
Triceratops were
Triceratops teeth were arranged in groups called batteries, which contained 36 to 40 tooth columns in each side of each jaw and 3 to 5 stacked teeth per column, depending on the size of the animal.[31] This gives a range of 432 to 800 teeth, of which only a fraction were in use at any given time (as tooth replacement was continuous throughout the life of the animal).[31] They functioned by shearing in a vertical to near-vertical orientation.[31] The great size and numerous teeth of Triceratops suggests that they ate large volumes of fibrous plant material. Some researchers suggest it ate palms and cycads[60][61] and others suggest it ate ferns, which then grew in prairies.[62]
Functions of the horns and frill
There has been much speculation over the functions of Triceratops' head adornments. The two main theories have revolved around use in combat and in courtship display, with the latter now thought to be the most likely primary function.[31]
Early on, Lull postulated that the frills may have served as anchor points for the jaw muscles to aid chewing by allowing increased size and power for the muscles.[63] This has been put forward by other authors over the years, but later studies do not find evidence of large muscle attachments on the frill bones.[64]
Triceratops were long thought to have used their horns and frills in combat with large predators, such as
In addition to combat with predators using its horns, Triceratops are popularly shown engaging each other in combat with horns locked. While studies show that such activity would be feasible, if unlike that of present-day horned animals,[68] there is disagreement about whether they did so. Although pitting, holes, lesions, and other damage on Triceratops skulls (and the skulls of other ceratopsids) are often attributed to horn damage in combat, a 2006 study finds no evidence for horn thrust injuries causing these forms of damage (with there being no evidence of infection or healing). Instead, non-pathological bone resorption, or unknown bone diseases, are suggested as causes.[69] A newer study compared incidence rates of skull lesions and periosteal reaction in Triceratops and Centrosaurus, showing that these were consistent with Triceratops using its horns in combat and the frill being adapted as a protective structure, while lower pathology rates in Centrosaurus may indicate visual use over physical use of cranial ornamentation or a form of combat focused on the body rather than the head.[70] The frequency of injury was found to be 14% in Triceratops.[71] The researchers also concluded that the damage found on the specimens in the study was often too localized to be caused by bone disease.[72] Histological examination reveals that the frill of Triceratops is composed of fibrolamellar bone.[73] This contains fibroblasts that play a critical role in wound healing and is capable of rapidly depositing bone during remodeling.[74][75]
One skull was found with a hole in the jugal bone, apparently a puncture wound sustained while the animal was alive, as indicated by signs of healing. The hole has a diameter close to that of the distal end of a Triceratops horn. This and other apparent healed wounds in the skulls of ceratopsians has been cited as evidence of non-fatal intraspecific competition in these dinosaurs.[76][77] Another specimen, referred to as "Big John", has a similar fenestra to the squamosal caused by what appears to be another Triceratops horn and the squamosal bone shows signs of significant healing, further vindicating the hypothesis that this ceratopsian used its horns for intra-specific combat.[78]
The large frill also may have helped to increase body area to regulate body temperature.[79] A similar theory has been proposed regarding the plates of Stegosaurus,[80] although this use alone would not account for the bizarre and extravagant variation seen in different members of Ceratopsidae, which would rather support the sexual display theory.[31]
The theory that frills functioned as a sexual display was first proposed by Davitashvili in 1961 and has gained increasing acceptance since.[19][64][81] Evidence that visual display was important, either in courtship or other social behavior, can be seen in the ceratopsians differing markedly in their adornments, making each species highly distinctive. Also, modern living creatures with such displays of horns and adornments use them similarly.[82] A 2006 study of the smallest Triceratops skull, ascertained to be a juvenile, shows the frill and horns developed at a very early age, predating sexual development and probably important for visual communication and species recognition in general.[83] The use of the exaggerated structures to enable dinosaurs to recognize their own species has been questioned, as no such function exists for such structures in modern species.[84]
Growth and ontogeny
In 2006, the first extensive ontogenetic study of Triceratops was published in the journal
Torosaurus as growth stage of Triceratops
Torosaurus is a ceratopsid genus first identified from a pair of skulls in 1891, two years after the identification of Triceratops by Othneil Charles Marsh. The genus Torosaurus resembles Triceratops in geological age, distribution, anatomy, and size, so it has been recognised as a close relative.[86] Its distinguishing features are an elongated skull and the presence of two ovular fenestrae in the frill. Paleontologists investigating dinosaur ontogeny in Montana's Hell Creek Formation have recently presented evidence that the two represent a single genus.
John Scannella, in a paper presented in Bristol at the conference of the Society of Vertebrate Paleontology (September 25, 2009), reclassified Torosaurus as especially mature Triceratops individuals, perhaps representing a single sex. Horner, Scannella's mentor at Bozeman Campus, Montana State University, noted that ceratopsian skulls consist of metaplastic bone. A characteristic of metaplastic bone is that it lengthens and shortens over time, extending and resorbing to form new shapes. Significant variety is seen even in those skulls already identified as Triceratops, Horner said, "where the horn orientation is backwards in juveniles and forward in adults". Approximately 50% of all subadult Triceratops skulls have two thin areas in the frill that correspond with the placement of "holes" in Torosaurus skulls, suggesting that holes developed to offset the weight that would otherwise have been added as maturing Triceratops individuals grew longer frills.[87] A paper describing these findings in detail was published in July 2010 by Scannella and Horner. It formally argues that Torosaurus and the similar contemporary Nedoceratops are synonymous with Triceratops.[29]
The assertion has since ignited much debate. Andrew Farke had, in 2006, stressed that no systematic differences could be found between Torosaurus and Triceratops, apart from the frill.
Other genera as growth stages of Triceratops
Opinion has varied on the validity of a separate genus for Nedoceratops. Scannella and Horner regarded it as an intermediate growth stage between Triceratops and Torosaurus.[29][91] Farke, in his 2011 redescription of the only known skull, concluded that it was an aged individual of its own valid taxon, Nedoceratops hatcheri.[88] Longrich and Fields also did not consider it a transition between Torosaurus and Triceratops, suggesting that the frill holes were pathological.[90]
As described above, Scannella had argued in 2010 that Nedoceratops should be considered a synonym of Triceratops.[29] Farke (2011) maintained that it represents a valid distinct genus.[88] Longrich agreed with Scannella about Nedoceratops and made a further suggestion that the recently described Ojoceratops was likewise a synonym. The fossils, he argued, are indistinguishable from the Triceratops horridus specimens that were previously attributed to the defunct species Triceratops serratus.
Longrich observed that another newly described genus, Tatankaceratops, displayed a strange mix of characteristics already found in adult and juvenile Triceratops. Rather than representing a distinct genus, Tatankaceratops could as easily represent a dwarf Triceratops or a Triceratops individual with a developmental disorder that caused it to stop growing prematurely.[92]
Paleoecology
Triceratops lived during the Late Cretaceous of western North America, its fossils coming from the Evanston Formation, Scollard Formation, Laramie Formation, Lance Formation, Denver Formation, and Hell Creek Formation.[93] These fossil formations date back to the time of the Cretaceous–Paleogene extinction event, which has been dated to 66 ± 0.07 million years ago.[94] Many animals and plants have been found in these formations, but mostly from the Lance Formation and Hell Creek Formation.[93] Triceratops was one of the last ceratopsian genera to appear before the end of the Mesozoic. The related Torosaurus and more distantly related diminutive Leptoceratops were also present, though their remains have been rarely encountered.[9]
Theropods from these formations include genera of
, and an undescribed specimen from North Dakota. The first two might be junior synonyms of Pachycephalosaurus.Cultural significance
Triceratops is the official
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External links
- Media related to Triceratops at Wikimedia Commons
- Wikijunior Dinosaurs/Triceratops at Wikibooks
- Works related to Notice of Gigantic Horned Dinosauria from the Cretaceous at Wikisource
- Data related to Triceratops at Wikispecies
- Triceratops at The Dinosaur Picture Database
- LiveScience: Facts about Triceratops at LiveScience.com
- Clash of the Dinosaurs: The Defenders – The Triceratops Threat on YouTube
- Dinosaur Mailing List post on Triceratops stance Archived October 13, 2007, at the Wayback Machine
- Smithsonian Exhibit
- Triceratops in the Dino Directory
- Triceratops (short summary and good color illustration)
- Triceratops For Kids (a fact sheet about the Triceratops with activities for kids)
- Triceratops, BBC Dinosaurs
- (in French) Triceratops Archived October 17, 2016, at the Wayback Machine – Liste de Dinosauria et Extinction