Triceratops

Triceratops (lit. 'three-horned face') is a genus of chasmosaurine ceratopsian dinosaur. It lived during the late Maastrichtian age of the Late Cretaceous period, about 69 to 66 million years ago, on the island continent of Laramidia, which is now western North America. It was one of the last dinosaurs that were not birds. It lived until the Cretaceous–Paleogene extinction event, 66 million years ago. For the band, see Triceratops (band).

The name Triceratops comes from Ancient Greek words meaning 'three', 'horn', and 'face'. It had a large bony frill, three horns on its skull, and a large body with four legs. Its body was shaped a bit like that of rhinoceroses, even though the two animals are not closely related. This is an example of convergent evolution. Triceratops is one of the most recognizable dinosaurs and the best-known ceratopsian.

Triceratops was also one of the largest of its kind. It was about 8–9 m (26–30 ft) long and weighed up to 6–10 t. It lived alongside Tyrannosaurus rex, which most likely hunted it.

Scientists have long wondered what the frills and horns were for. In the past, people thought they were weapons to defend against predators. Newer ideas suggest that these features were mainly used to tell species apart, attract mates, and show which animal was in charge.

Triceratops was once placed among the "short-frilled" ceratopsids. However, modern cladistic studies show that it belongs to Chasmosaurinae, a group that usually has long frills. Today, two species are considered valid, though seventeen different species have been named over time. The first scientific description of the genus was made in 1889 by American paleontologist Othniel Charles Marsh. Many remains have been found, from baby animals to adults. As the archetypal ceratopsian, Triceratops has appeared in many films, postage stamps, and other media.

Discovery and identification

See also: Timeline of ceratopsian research

The first named fossil linked to Triceratops was a pair of brow horns attached to a piece of skull. George Lyman Cannon found them near Denver, Colorado, in the spring of 1887. The fossil was sent to Othniel Charles Marsh, who first thought it came from a large, unusual bison. He named it Bison alticornis. The next year, he realized that these were horns from a dinosaur. Marsh's rival, Edward Drinker Cope, also named some older fossils that might belong to Triceratops. However, those remains were too incomplete to be sure. The main specimen used to describe Triceratops was collected in 1888 by fossil hunter John Bell Hatcher. At first, Marsh named it a different kind of Ceratops. When more of the skull was prepared, he gave it the new name Triceratops, which means "three-horn face."

After Triceratops was described, Hatcher carefully collected thirty-one more of its skulls. Scientists have discussed how many kinds, or species, of Triceratops existed. Early researchers sorted the skulls in different ways. The skulls vary a lot, partly because they came from animals of different ages and both sexes. In 1986, John Ostrom and Peter Wellnhofer proposed that there was only one species, Triceratops horridus. Later, paleontologist Catherine Forster studied the fossils more fully. She concluded that there were two species, T. horridus and T. prorsus. In 2014, John Scannella and his colleagues supported this idea. They noted that the two species lived at different times.

Description

Triceratops was a very large animal. It was about 8–9 meters (26–30 ft) long and weighed up to 6–10 metric tons (6.6–11.0 short tons). A T. horridus specimen named Kelsey was 6.7–7.3 meters (22–24 ft) long. It had a 2-meter (6.5 ft) skull and stood about 2.3 meters (7.5 ft) tall. The Black Hills Institute estimated that Kelsey weighed about 5.4 metric tons (6.0 short tons). A T. horridus specimen named Big John was estimated to be 8.0 meters (26.1 ft) long and 3.0 meters (10 ft) tall. Like all chasmosaurines, Triceratops had a large skull for its body size. It was one of the largest skulls of any land animal. The biggest known skull, specimen MWC 7584 (formerly BYU 12183), is estimated to have been 2.5 meters (8.2 ft) long. That is almost a third of the animal's length. A large beak sat in front of the teeth. It was built around a special rostral bone, with premaxillae bones behind it. A single horn sat on the snout above the nostrils. A pair of brow horns about 1 meter (3.3 ft) long sat above the eyes. The jugal bones pointed downward at the back sides of the skull. The frontal bones folded to form a "double" skull roof. Some specimens show a fontanelle, which is an opening in the upper roof layer. At the back of the skull, the squamosal bones and parietal bones formed a short frill. In young animals, the frill was decorated with epoccipitals. These were small triangular bony bumps, or osteoderms. Unlike most of its relatives, the frill was solid and had no fenestrae, which are openings. A large occipital condyle, up to 106 millimeters (4.2 in) across, connected the head to the neck. The articular bone at the back of the lower jaw was very wide.

Triceratops had a sturdy body, with strong limbs, short hands, and short feet. Chasmosaurines looked quite similar in their skeletons. Its vertebral column had ten neck, twelve back, ten sacral, and about forty-five tail vertebrae. Its front neck bones were fused into a syncervical. Earlier scientists thought this included the first three vertebrae. Later work supported an old idea by John Bell Hatcher. That idea said a small part of the real atlas, with its spinous process, could be seen at the very front. The back vertebrae had bone bands around the spinal canal. The sacrum, which connects to the pelvis, was fused in adults. Bone plates on top formed a shape like a carapace. The pelvis had a long ilium, and the ischium curved downward. It was certainly quadrupedal, but its posture has long been debated. People once believed its front legs stuck out sideways from the thorax. Paintings by Charles Knight and Rudolph Zallinger showed it this way. Newer ichnological evidence from trackways and skeleton models suggests it stood upright. This is similar to a modern rhinoceros. Tracks named Ceratopsipes goldenensis may have been made by Triceratops or the closely related Torosaurus. Its hands kept a fairly simple structure compared with thyreophorans and many sauropods. Like other ceratopsians, ornithopods (together forming the Cerapoda), and theropods, most of its fingers pointed out and away from the body. Only the first three fingers carried its weight, and its phalangeal formula shows this pattern. Fossil skin from Triceratops has also been found. A specimen nicknamed "Lane" (HMNS PV.1506) was found in Wyoming in 2002. It keeps large areas of skin and is on display at the Houston Museum of Natural Science. This skin is preserved as a thin layer of clay, not as real skin. Scientists learned this method from studying two Edmontosaurus "mummy" specimens. Its large scales could be up to 90 millimetres (3.5 in) across. Larger scattered scales had small cone-like bumps. It has been suggested that these bumps probably did not have bristles, unlike those of Psittacosaurus.

Classification

Triceratops is the best-known kind of Ceratopsidae, a family of large ceratopsians. Most of them lived in North America. For many years, scientists were not sure where Triceratops fit among its relatives. It had a short, solid frill like Centrosaurinae, but it had long brow horns like Chasmosaurinae. In an early overview of ceratopsians, R. S. Lull placed Triceratops with the centrosaurines. In 1949, Charles Mortram Sternberg disagreed. He said Triceratops was more closely related to Arrhinoceratops and Chasmosaurus, so it belonged with the chasmosaurines. Later discoveries and studies, including work by Peter Dodson, supported Sternberg's idea.

The cladogram below follows Longrich (2014), who named a new species of Pentaceratops. His study included almost all of the chasmosaurine species.

Scientists did not know much about the early family history of Triceratops for a long time. In 1922, Henry Fairfield Osborn thought the newly found Protoceratops was its ancestor. Newer discoveries have helped scientists understand how ceratopsians changed over time. One is Zuniceratops, the earliest known ceratopsian with brow horns. Another is Yinlong, the first known Jurassic ceratopsian. In phylogenetic taxonomy, Triceratops is also used as a reference point for defining Dinosauria. Dinosaurs are described as all the descendants of the most recent common ancestor of Triceratops and modern birds. Ornithischia includes the dinosaurs that are more closely related to Triceratops than to modern birds.

Paleobiology

Many people picture Triceratops as a herding animal, but there is little evidence that it lived in herds. Only one bone beds site is mostly Triceratops bones, and it holds the remains of three young animals. In 2012, three Triceratops of different sizes were found near Newcastle, Wyoming. They may have traveled together as a family. Their bones show signs of attack or scavenging by Tyrannosaurus. Paleontologist Peter Larson and the Black Hills Institute are studying these remains.

For many years, Triceratops fossils were known only from single animals. But they are very common. Bruce Erickson of the Science Museum of Minnesota reported seeing 200 specimens in the Hell Creek Formation of Montana. Barnum Brown said he had seen over 500 skulls in the field. Its fossils are so common in western North America at the end of the Late Cretaceous that it is seen as one of the most common plant-eaters of its time. Skulls are found much more often than postcranial bones, which suggests that skulls were especially likely to be preserved. In 1986, Robert Bakker estimated that Triceratops made up five sixths of the large dinosaurs of the Lancian faunal stage of the late Maastrichtian.

Studies of its skull suggest that Triceratops had a poor sense of smell, but its ears were good at hearing low sounds. It probably held its head about 45 degrees to the ground, which showed off its horns and frill while it grazed. A 2026 study suggested that its respiratory turbinates moistened the air it breathed, which cooled the blood going to the eyes and brain. A 2022 study suggested that it had a cold-blooded (ectothermic) or gigantothermic metabolism, similar to modern reptiles. Another study suggested it may have been warm-blooded (endothermic) because of its large body. Its environment included floodplains and inland forests.

Triceratops were herbivorous, which means they ate only plants. Because its head was low, it probably ate low-growing plants. It may have knocked down taller ones with its horns, beak, and bulk. Its teeth were arranged in groups called batteries. Many teeth were in use at once, and they were replaced throughout its life. Its diet may have included fibrous plant material, Populus, Pine, Platanus, Hazel, and Taxodium plants. It may also have eaten palms, cycads, and ferns.

There has been much discussion about the purpose of the horns and frill. The two main ideas were fighting and courtship display. Display is now thought to be the most likely main purpose. Early on, Lull suggested the frill helped anchor jaw muscles, but later studies did not find evidence for this. For a long time, scientists thought Triceratops used its horns against predators such as Tyrannosaurus. Charles H. Sternberg first discussed this idea in 1917. Fossil bite marks on a Triceratops horn and squamosal show that the two animals did meet head-on. However, it is not known which animal attacked. Other Triceratops fossils show that Tyrannosaurus also fed on them.

Some damage on Triceratops skulls was once blamed on fights between horns, but a 2006 study found no evidence for this. A 2009 study suggested that the frill protected the animal, and that its horns were used in fights. One skull has a hole in the jugal bone that healed while the animal was alive. This suggests that Triceratops fought with others of its own kind and survived. The frill may also have helped control body temperature, but this idea does not explain the wide variety of frill shapes. The idea that frills were used in courtship display was first proposed in 1961 and has gained support since. A 2006 study found that the frill and horns developed at a very early age. This suggests they were important for communication and for recognizing members of the same kind.

In 2006, John R. Horner and Mark Goodwin published the first large study of how Triceratops grew. They sorted the animals into four general groups: babies, juveniles, subadults, and adults. Each group had its own features, and the horns changed shape as the animals grew.

Main article: Torosaurus

Torosaurus was first identified in 1891 from a pair of skulls. It was similar to Triceratops in age, location, and size. However, it had a longer skull and two holes in its frill. In 2009, John Scannella suggested that Torosaurus was actually a fully grown form of Triceratops. Horner and Scannella later argued this in print. Other scientists disagreed, pointing out that Triceratops and Torosaurus differed in ways that would be unusual for growth. Later studies by Farke and Maiorino concluded that they were separate kinds of dinosaurs, though the question is still debated. In 2022, researchers argued that some young specimens from Canada were a kind of Torosaurus.

Main article: Nedoceratops

Scientists have disagreed about whether Nedoceratops was a separate genus. Some considered it a growth stage of Triceratops. Farke concluded that it was a valid kind of its own. Other researchers suggested that some newly described animals were also Triceratops, or young animals with unusual features.

Paleoecology

Triceratops lived in the Late Cretaceous in western North America. Its fossils have been found in the Evanston Formation, Scollard Formation, Laramie Formation, Lance Formation, Denver Formation, and Hell Creek Formation. These rock layers date to the time of the Cretaceous–Paleogene extinction event, about 66 million years ago. Many animals and plants have been found in them, mostly from the Lance and Hell Creek Formations. Triceratops was one of the last ceratopsians to appear before the end of the Mesozoic. The related Torosaurus and the much more distantly related, smaller Leptoceratops also lived there, though their remains are rarely found. Chemical studies suggest that Triceratops fossils from DTB (Darnell Triceratops Bonebed) may have lived on freshwater floodplains, although they likely did not live in only one kind of place.

Meat-eating dinosaurs from these rock layers include groups of dromaeosaurids, tyrannosaurids, ornithomimids, troodontids, avialans, and caenagnathids. From the Hell Creek Formation, dromaeosaurids include Acheroraptor and Dakotaraptor. Some teeth once linked to Dromaeosaurus and Saurornitholestes are now thought to belong to Acheroraptor. Tyrannosauroids include Nanotyrannus and Tyrannosaurus. Ornithomimids include Struthiomimus and Ornithomimus, and an animal called "Orcomimus," which has not been formally described, may also be from the formation. Troodontids include Pectinodon and Paronychodon from the Hell Creek Formation, and a possible species of Troodon from the Lance Formation. Teeth from an unknown coelurosaur, named Richardoestesia, are found in the Hell Creek and similar formations. Oviraptorosaurs from the Hell Creek Formation include Anzu. Avialans include Avisaurus, several species of Brodavis, other hesperornithoforms, and several true birds, including Cimolopteryx.

Ornithischians are common in the Scollard, Laramie, Lance, Denver, and Hell Creek Formations. Their main groups are ankylosaurians, ornithopods, ceratopsians, and pachycephalosaurians. Three ankylosaurians are known: Ankylosaurus, Denversaurus, and possibly a species of Edmontonia or a genus that has not been named. Other ceratopsians from these formations include the leptoceratopsid Leptoceratops and the chasmosaurine ceratopsids Torosaurus, Nedoceratops, and Tatankaceratops. Ornithopods are common in the Hell Creek Formation, with several species of the thescelosaurine Thescelosaurus and the hadrosaurid Edmontosaurus. Several pachycephalosaurians have been found in the Hell Creek Formation and similar formations, including the pachycephalosaurids Stygimoloch, Dracorex, Pachycephalosaurus, Sphaerotholus, and an unnamed specimen from North Dakota. The first two might be junior synonyms of Pachycephalosaurus.

Mammals are plentiful in the Hell Creek Formation. Groups include multituberculates, metatherians, and eutherians. The multituberculates include Paracimexomys, the cimolomyids Paressonodon, Meniscoessus, Essonodon, Cimolomys, Cimolodon, and Cimexomys, and the neoplagiaulacids Mesodma and Neoplagiaulax. The metatherians include the alphadontids Alphadon, Protalphodon, and Turgidodon, the pediomyids Pediomys, Protolambda, and Leptalestes, the stagodontid Didelphodon, the deltatheridiid Nanocuris, the herpetotheriid Nortedelphys, and the glasbiid Glasbius. A few eutherians are known, including Alostera, Protungulatum, the cimolestids Cimolestes and Batodon, the gypsonictopsid Gypsonictops, and the possible nyctitheriid Paranyctoides.

Cultural significance

See also: Cultural depictions of dinosaurs

Since the early 1900s, Triceratops has been one of the most famous dinosaurs. It is a well-known example of the ceratopsian dinosaurs. Museums often show it to the public because many of its fossils have been found. A mounted Triceratops skeleton was shown at the 1900 Paris Exposition. This may have been the first time the dinosaur was put on display. About 21,000 visitors saw it in the first two days. A model of Triceratops by American sculptor Louis Paul Jonas was also shown at the 1964 New York World's Fair.

Triceratops appears in many dinosaur films, including The Lost World (1925) and Jurassic Park (1993). In books, Edgar Rice Burroughs called these animals "Gryfs" in his 1921 novel Tarzan the Terrible. In the 1956 children's book The Enormous Egg by Oliver Butterworth, a Triceratops hatches from a chicken egg. After Tyrannosaurus and Stegosaurus, it is the dinosaur shown most often on stamps. Triceratops is the official state fossil of South Dakota and the official state dinosaur of Wyoming. In 1928, Charles R. Knight painted a mural at the Field Museum of Natural History in Chicago. It showed a Tyrannosaurus facing a Triceratops, which helped people think of the two animals as rivals. Paleontologist Robert Bakker said that the two giants made a dramatic match. He described them as rivals in the last days of the last epoch of the Age of Dinosaurs.