Although
Triceratops is commonly portrayed as a
herding animal, there is currently little evidence to suggest that they lived in herds. While several other ceratopsians are known from
bone beds preserving bones from two to hundreds or even thousands of individuals, there is currently only one documented bonebed dominated by
Triceratops bones: a site in southeastern Montana with the remains of three juveniles. It may be significant that only juveniles were present. In 2012, a group of three
Triceratops in relatively complete condition, each of varying sizes from a full-grown adult to a small juvenile, were found near
Newcastle, Wyoming. The remains are currently under excavation by paleontologist Peter Larson and a team from the
Black Hills Institute. It is believed that the animals were traveling as a family unit, but it remains unknown if the group consists of a mated pair and their offspring, or two females and a juvenile they were caring for. The remains also show signs of predation or scavenging from
Tyrannosaurus, particularly on the largest specimen, with the bones of the front limbs showing breakage and puncture wounds from
Tyrannosaurus teeth. In 2020, Illies and Fowler described the
co-ossified distal caudal vertebrae of
Triceratops. According to them, this pathology could have arisen after one
Triceratops accidentally stepped on the tail of another member of the herd. tooth marks at the middle For many years,
Triceratops finds were known only from solitary individuals. Similarly,
Barnum Brown claimed to have seen over 500 skulls in the field. Unlike most animals, skull fossils are far more common than
postcranial bones for
Triceratops, suggesting that the skull had an unusually high
preservation potential. at
Minnesota Science Museum 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. A 2026 study of the large nasal region suggested that
Triceratops likely had
respiratory turbinates which contained moisture that evaporated as air was inhaled. This released heat and cooled the blood directed to the eyes and brain, which would otherwise overheat within their large, thick skulls. The study also found that in ceratopsians, the lateral nasal nerve supplied the beak rather than the
maxillary nerve as in other reptiles. The latter's path was obstructed by the beak and nasal cavity. A 2022 study by Wiemann and colleagues of various dinosaur genera, including
Triceratops, suggests that it had an
ectothermic (cold blooded) or
gigantothermic metabolism, on par with that of modern reptiles. This was uncovered using the
spectroscopy of lipoxidation signals, which are byproducts of
oxidative phosphorylation and correlate with metabolic rates. They suggested that such metabolisms may have been common for ornithischian dinosaurs in general, with the group evolving towards ectothermy from an ancestor with an
endothermic (warm blooded) metabolism. An isotopic analysis study by Rooij and colleagues suggested that
Triceratops was gigantothermic, if not endothermic due to its large body volume. The jaws were tipped with a deep, narrow beak, believed to have been better at grasping and plucking than biting. The great size and numerous teeth of
Triceratops suggests that they ate large volumes of
fibrous plant material. Other plants that were a part of its diet included
Populus plants,
Pine plants,
Platanus plants,
Hazel plants, and
Taxodium plants. Some researchers suggest it, along with its cousin
Torosaurus ate
palms and
cycads and others suggest it ate
ferns, which then grew in prairies. Studies of the isotopes of ceratopsian and hadrosaur teeth revealed that
Triceratops and
Edmontosaurus respectively engaged in
niche partitioning.
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. 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.
Triceratops were long thought to have used their horns and frills in combat with large predators, such as
Tyrannosaurus, the idea being discussed first by
Charles H. Sternberg in 1917 and 70 years later by Robert Bakker. There is evidence that
Tyrannosaurus did have aggressive head-on encounters with
Triceratops, based on partially healed tyrannosaur tooth marks on a
Triceratops brow horn and
squamosal. The bitten horn is also broken, with new bone growth after the break. Which animal was the aggressor, however, is unknown. Paleontologist Peter Dodson estimates that, in a battle against a bull
Tyrannosaurus, the
Triceratops had the upper hand and would successfully defend itself by inflicting fatal wounds to the
Tyrannosaurus using its sharp horns.
Tyrannosaurus is also known to have fed on
Triceratops, as shown by a heavily tooth-scored
Triceratops ilium and
sacrum. 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, 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. A 2009 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. The frequency of injury was found to be 14% in
Triceratops. The researchers also concluded that the damage found on the specimens in the study was often too localized to be caused by bone disease. Histological examination reveals that the frill of
Triceratops is composed of fibrolamellar bone. This contains
fibroblasts that play a critical role in wound healing and is capable of rapidly depositing bone during remodeling. bone in selected specimens of
Triceratops 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 have been cited as evidence of non-fatal intra-specific competition in these dinosaurs. 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. The large frill also may have helped to increase body area to
regulate body temperature. A similar theory has been proposed regarding the plates of
Stegosaurus, 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. 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. However, 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.
Growth and ontogeny In 2006, the first extensive ontogenetic study of
Triceratops was published in the journal
Proceedings of the Royal Society. The study, by
John R. Horner and Mark Goodwin, found that individuals of
Triceratops could be divided into four general ontogenetic groups: babies, juveniles, subadults, and adults. With a total number of 28 skulls studied, the youngest was only long. Ten of the 28 skulls could be placed in order in a growth series with one representing each age. Each of the four growth stages were found to have identifying features. Multiple ontogenetic trends were discovered, including the size reduction of the epoccipitals, development and reorientation of postorbital horns, and hollowing out of the horns.
Big John, one of the
Triceratops, is estimated to have lived around 60 years when he died.
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. 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 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. 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. In 2013, Farke and Leonardo Maiorino published
morphometric research, a statistical analysis of the
morphospace (shape space) describing the variation of the
Torosaurus,
Triceratops horridus,
Triceratops prorsus, and
Nedoceratops skulls correlated with maturation. They concluded that
Torosaurus latus skulls throughout maturation retained a different form from
T. horridus and
T. prorsus, the last two species showing an overlapping in their proportions. This is even true when the frill shape is disregarded.
Nedoceratops proved, except for size, not to be a plausible transitional form between
Torosaurus and
Triceratops horridus. Farke and Maiorino admitted that the low number of
Torosaurus specimens reduced the reliability of these results, but concluded that
Torosaurus and
Triceratops were separate taxa, though allowing for the possibility of anagenesis, i.e. the several taxa forming a single
chronospecies line of descent, given the lack of good stratigraphic data. The morphometric study was inconclusive on the point of
Torosaurus utahensis, for which most specimens consist of isolated bones, with its morphospace falling in between
Triceratops and
Torosaurus latus and not well separated from either. In 2022, Mallon
et al. argued that two specimens found in Canada's
Frenchman and
Scollard Formations, EM P16.1. (at Eastend Historical Museum in Saskatchewan) and UALVP 1646 (at the
University of Alberta), are subadults and can be referred to
Torosaurus, this indicating that it is a valid taxon. The same study also noted that
Torosaurus indeed lived during the Late
Maastrichtian (contemporaneously with
Triceratops).
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. Farke, in his 2011 redescription of the only known skull, concluded that it was an aged individual of its own valid
taxon,
Nedoceratops hatcheri. Longrich and Fields also did not consider it a transition between
Torosaurus and
Triceratops, suggesting that the frill holes were pathological. ==Paleoecology==