Pachycephalosaurus wyomingensis (S/F)

Pachycephalosaurus wyomingensis is a species of large pachycephalosaurid dinosaur found in North America. It is the archetype of its family, with a genus name meaning “thick-headed reptile” in reference to its nine-inch-thick (22 centimeters) skull dome. The specific epithet means “from Wyoming,” the U.S. state where its fossils were first discovered. This dinosaur originally lived during the late Cretaceous period, between 70 and 66 million years ago, during the Maastrichtian age. It was among the last dinosaurs to live before the Cretaceous-Paleogene mass extinction event. Fossils have been found in the U.S. states of Wyoming, Montana, and South Dakota, as well as the Canadian province of Alberta.

Fossils of Pachycephalosaurus were first found during the late 1850s, possibly in 1859 or 1860, by American geologist Ferdinand Vandeveer Hayden. A bone fragment was found near the Missouri River in an area now known as the Lance Formation. It was identified as an osteoderm by biologist Joseph Leidy in 1872, who believed it came from either a lizard or an armored mammal similar to an armadillo. The bone was assigned to a new genus, Tylosteus, meaning “knob bone.” Its true identity would not be recognized until a century later, when Donald Baird identified it part of a pachycephalosaur squamosal bone, not a lizard or armadillo’s osteoderm. This fossil was eventually reassigned to Stygimoloch.

The naming of Pachycephalosaurus occurred in the early twentieth century, after fossilized remains had already been uncovered for some time. Fossil hunters Othniel Charles Marsh and Edward Drinker Cope found several fossils now known to belong to this species during the Bone Wars, a bitter rivalry between the two scientists. The first was discovered by Marsh’s associate John Bell Hatcher in the Lance Formation of Wyoming, though Marsh believed the bone (once again part of a squamosal) belonged to a Triceratops. Other remains including teeth were found, assigned to wholly different types of dinosaurs, and eventually discovered by later paleontologists to have been misidentified. Many of the fossils found by Hatcher for Marsh are now known to be Pachycephalosaurus remains.

Illustration of a mature P. wyomingensis

In 1931, paleontologist Charles Whitney Gilmore recognized these finds as belonging to a pachycephalosaur, though he named it Troodon wyomingensis (since, at the time, Troodon was mistakenly thought to be a pachycephalosaur). The genus Pachycephalosaurus was finally created by Barnum Brown and Erich Maren Schlaikjer in 1943, based on skull remains. They described two species: P. grangeri, known from the Hell Creek Formation, and P. reinheimeri, which was from the Lance Formation. “Troodonwyomingensis was renamed into a species of Pachycephalosaurus. After a confusing few decades of taxonomic revisions, a final conclusion was reached in 1983: there was only one species, and since P. wyomingensis was named first, that became the species’s official name. The older Tylosteus was dropped from usage since it had been neglected for fifty years.

While there is still only one recognized species of Pachycephalosaurus, taxonomic revisions have continued into the present day regarding supposed close relatives. The smaller pachycephalosaurs, Dracorex and Stygimoloch, lived in the same time and place as Pachycephalosaurus and resemble juveniles of this larger dinosaur. Many paleontologists, including Jack Horner, believe that they represent different growth stages and not different species. Today, the majority of paleontologists agree. More Pachycephalosaurus remains have been found from the 2010s onward too; the Scollard Formation in Alberta, Canada has yielded fossils, suggesting that Pachycephalosaurus roamed farther north than once assumed.

In the late 1980s or early 1990s, while knowledge of this dinosaur was still developing, International Genetic Technologies succeeded in bringing it back from extinction by cloning modified ancient DNA found in Maastrichtian amber samples. Later, they also engineered Stygimoloch, which most paleontologists believe to be synonymous with Pachycephalosaurus; it is possible that InGen created their Stygimoloch by modifying Pachycephalosaurus to retain its juvenile traits. The origins of InGen Stygimoloch are not currently well-known, so any speculation is without evidence.


Paleontologists historically had little material from Pachycephalosaurus to work with, since most of the known fossils were parts of the skull. More complete remains have only been discovered recently, illuminating the differences between the original animal and InGen clones. The recreated form of this dinosaur grows between 13 and 16 feet (4 to 5 meters) from head to tail, and reaches five to six feet (1.5 to 2 meters) tall. It is bulky, with weight ranging from 800 to 1,000 pounds (about 365 to 450 kilograms) at its adult size. InGen Pachycephalosaurus are similar in size to their fossil counterparts, but bodily proportions are noticeably different; their stance is much more upright, often assuming a tripod posture with the tail held near the ground. The neck is thicker, though it still attaches to the back of the skull in a fashion to help the body absorb impacts to the head.

The skull of Pachycephalosaurus is its most distinct feature. In adulthood, the skull is adorned with a dome of solid bone which can reach nine to ten inches thick, with some added thickness from keratin. This protects the dinosaur’s brain, which is quite small. Although it is not intelligent by any means, its senses are good, particularly its vision; the round, bird-like eyes face forward, giving it binocular vision. The sclerae are an amber color. Its mouth is beaked, and unlike its ancestor, it has extensive cheeks for holding food when it eats. Because of the cheeks, InGen specimens have a much smaller gape than ancestral Pachycephalosaurus, restricting how wide their mouths can open. Along with the skull dome, the head of Pachycephalosaurus is ornately decorated with blunt spines, bumps, and knobs, particularly around the rim of the dome and on the snout. Some have a larger, pointier bump on the nose resembling a small horn. Its teeth are arranged with blade-like incisors in the front and leaf-shaped cutting teeth in the back.

Damage sustained to the skull ornamentation may help to differentiate between individual Pachycephalosaurus. While their domes are resilient, they are not indestructible, and will collect scratches and chips as the animal fights both predators and rivals. As the animal survives more fights, the bumps and spikes on its head will sustain damage as well. Injuries like these are common: a study in 2013 by Joseph Peterson described 22% of pachycephalosaur skulls showing signs of osteomyelitis resulting from head trauma (for further reading, see Cranial Pathologies in a Specimen of Pachycephalosaurus). The domes are made of unique fibrolamellar bone, containing fibroblasts that rapidly deposit during bone remodeling and grant pachycephalosaurs a quick healing process.

Its neck is short but strong, and when it lowers its head, the spine is straightened out to turn the animal into a full-body battering ram. This differs from the fossil animal, in which the neck is carried in a U-shape and thus its whole body cannot achieve a totally horizontal posture. The arms are relatively weak, used mostly for grasping food with its five-fingered hands, but the legs are powerful and can push a Pachycephalosaurus along at a solid pace. The feet have four toes, though only three of them actually contact the ground; the fourth is a dewclaw, and is vestigial. Pachycephalosaurus has a heavy tail that makes up about half the length of its body and is kept rigid by ossified tendons. This helps it keep balance while running, and counters the weight of its thick head.

Newer version of P. wyomingensis

Coloration in this dinosaur comes in two main patterns. The first was present on InGen’s earlier specimens, and has historically been the more common color scheme; its base is beige or tan, with dark blue and gray patterning. The patterns appear on the face (particularly around the eyes) and as stripes down its neck, shoulders, back, hips, and tail. Its underbelly is slightly lighter in color, and the dome is lightest-colored of all. Darker colors are usually present on the snout, particularly the beak, which may appear almost black. The second color scheme was present on newer animals bred after InGen was bought out by Masrani Global Corporation in 1997, and is fairly rare. In these specimens, a lighter creamy off-white rather than beige makes the base of the creature’s pelt, and the patterning is light brown. This brown color occurs on the neck, most of the back, and the fore parts of the arms and legs, with cream-colored spotting throughout. Another stripe of brown rings the head between the snout and eyes, while the snout itself as well as the surroundings of the eyes and ears are cream-colored. Scales on its body are variable in size but overall give its skin a pebbly texture.

Pachycephalosaurus in the embryonic stage

Upon hatching, Pachycephalosaurus has a flat skull rather than the characteristic rounded dome of the adult. Most paleontologists believe Dracorex to represent the juvenile form of Pachycephalosaurus, while Stygimoloch is believed to be an adolescent. InGen has created specimens of these different animals that appear to be separate genera, but they may potentially have deliberately engineered some lineages of Pachycephalosaurus to retain juvenile traits, unless these dinosaurs really are separate.

In any case, young Pachycephalosaurus develop spines on their skulls before their domes start to grow. Eventually, their domes become round as they begin maturing. The nearer they get to adulthood, the taller the domes become, reaching a full thickness of up to ten inches when completely mature. As they age, their cranial spines wear down and become smaller, shrinking as the dome grows. By the time they are fully grown, the spines have weathered away to knobs and bumps. The growth rate of Pachycephalosaurus is not known, nor is its average lifespan; genetically-engineered specimens may not show the same life history patterns as the original animals.

Sexual Dimorphism

Although some scientists have speculated that female Pachycephalosaurus might have smaller domes and less ornate heads, this has not yet been observed directly. Sexual dimorphism in this species remains unknown.

Preferred Habitat

This dinosaur prefers prairie or savanna regions for feeding, but the presence of larger predators means that it does need some amount of shelter. Therefore, it is found around the edges of forests and mountains, where trees and large rocks give it places it can hide. Mountainous foothills seem to be ideal. It also seeks out sources of calm fresh water such as rivers and wetlands. An ideal habitat for this dinosaur is a careful balance of open plains and sheltering structure, with fruit-bearing plants and clean water around.

Muertes Archipelago

International Genetic Technologies began cloning Pachycephalosaurus at their Isla Sorna laboratory facility sometime during either the late 1980s or early 1990s, originally intending to ship adults to Isla Nublar for exhibition in the Jurassic Park theme park. However, none were approved for exhibition by 1993, suggesting that this might have been one of the more recent species cloned. As of June 1993, there were nine pachys counted by InGen staff on Isla Sorna; the region that they were kept in is currently undisclosed.

InGen activity on Isla Sorna was drastically decreased due to financial stresses encountered in 1993, including a serious incident which shuttered the Isla Nublar facilities. InGen’s President, John Hammond, argued for Isla Sorna to become a secret wildlife preserve for de-extinct animals and slowed down much of the operations there, so population statistics are unavailable. Hurricane Clarissa eventually forced the complete evacuation of Isla Sorna, and the dinosaurs were turned out into the wild where, it was assumed, they would die. However, evidence had been mounting that the dinosaurs’ extinction was not guaranteed. This was confirmed by 1996, as infrared scanning detected Pachycephalosaurus thriving in the southwestern region of Isla Sorna. People physically went to the island in May 1997, encountering a herd of around seventeen adult and subadult Pachycephalosaurus on a game trail in the island’s northeast. With two distinct populations of this dinosaur on the island, it seems to have bred very successfully between 1993 and 1997. Their proliferation was counteracted by the presence of predators, such as Tyrannosaurus rex, which is known to have fed upon them.

Human intervention on Isla Sorna did not subside, beginning with an ill-fated attempt to capture this dinosaur by InGen. At least two adults, including a male nicknamed Friar Tuck, were captured by the InGen Harvester expedition before being released by animal rights activists somewhat near their usual habitat. From then on, the island was visited frequently and illegally by all manner of people, and the ecosystem suffered. Worst of all was InGen’s covert use of the island in 1998 to research and practice de-extinction in violation of U.S. law, which introduced a large number of new animals and promptly abandoned them. The island, unable to sustain its burgeoning population any longer, experienced a trophic cascade which caused numerous animals to become locally extinct. Survivors were captured by Masrani Global Corporation, which had bought InGen, and transported to Isla Nublar in 2004 and 2005. Others were captured by poachers, and brought to parts unknown. Isla Sorna’s status is now heavily guarded, with the United Nations and Masrani Global restricting access. Official records state that no de-extinct life is left on the island, but there is evidence to the contrary. This makes the status of Pachycephalosaurus on Isla Sorna a mystery. None are known from other islands of the archipelago.

Jurassic Park: San Diego

This was among several species InGen intended to exhibit in Jurassic Park: San Diego. While the location had been abandoned in the 1980s when InGen’s CEO John Hammond decided to instead build on an exotic island, Hammond’s successor Peter Ludlow attempted to revive the San Diego location in 1997. Despite his efforts, no Pachycephalosaurus were successfully brought off of Isla Sorna, and so their exhibit in the Park remained unpopulated.

Isla Nublar

Between the autumn of 2004 and the spring of 2005, populations of this animal were transported from Isla Sorna to Isla Nublar, where they were put on exhibition in Jurassic World. Population statistics for this period of time are not currently known, but a decent number of Pachycephalosaurus were kept in the park. Their main attraction was the Pachy Arena, but this does not seem to have been where they were housed; it appears to have served mainly as a theater and not a living space. Instead, the Pachycephalosaurus lived most of their time someplace in the central valley, near other herbivorous dinosaurs in habitat attractions such as Triceratops Territory. New pachys were most likely bred for the park as well, and would have hatched in the Hammond Creation Lab. They would spend a few months here before eventually being introduced to the park.

Sometimes, Pachycephalosaurus would roam outside their designated zone after headbutting contests caused their RFID tracking implants to short out. Normally, these implants would give them a mild shock if they attempted to cross the invisible fence barriers around their habitat. They seem to have been a particular problem for this technology; on December 22, 2015, an adult male Pachycephalosaurus roamed into the West Plains area and had to be sedated by the Asset Containment Unit for relocation back into its proper zone. According to Jurassic World’s Senior Asset Manager Claire Dearing, two other similar incidents had occurred that month.

On the same day as that incident, a more serious safety scandal occurred at Jurassic World, resulting in the park’s indefinite closure. The Pachycephalosaurus, among the other dinosaurs, were allowed to roam freely as their invisible fences were deactivated. Presumably, any pachys within the Arena were already removed to their living space for the night by the time the park’s closure became official. But once they were all in the wild, they would have to contend with predators, resource scarcity, and a lack of medical care; their populations suffered as a result. Many starved, died of disease, or were eaten by other animals. By 2017, their population appeared to consist of a single herd located in the northern mountains, particularly the foothills of Mount Sibo.

In early 2017, the mountain began to show signs of volcanic activity. The pachy population persisted into 2018, lasting up until the late spring or early summer. Poaching occurred on the island, but it is not known whether any of this species were captured. The volcanic activity worsened, with ashfall and toxic gas emission threatening the dinosaurs. Since the Pachycephalosaurus herd lived very close to the volcano, they were among the most heavily affected species, and they were pushed to the brink of extinction. On June 22, 2018, Mount Sibo’s eruption turned violent, likely obliterating all the remaining Pachycephalosaurus on Isla Nublar. They are now believed to be regionally extinct.

Mantah Corp Island

During the years of Jurassic World’s operation, numerous de-extinct animal species were appropriated by InGen’s rival Mantah Corporation, which had constructed a facility on Mantah Corp Island for studying and exploiting the animals. No Pachycephalosaurus have currently been confirmed among their menagerie.

BioSyn Genetics Sanctuary

Following the release of de-extinct animals into the wild in 2018, several governments have authorized BioSyn Genetics to round up and relocate problematic creatures in cooperation with the Department of Prehistoric Wildlife. Although Pachycephalosaurus has not been reported among the creatures of the BioSyn Genetics Sanctuary, it is not impossible that this often-trafficked species was acquired by the company. As of spring 2022, the facility is now partly administered by the United Nations, which oversees operations there.

Black market

This dinosaur may have been poached from Isla Sorna or Isla Nublar between 1997 and 2018, though due to the illicit nature of such acts, details are scarce. The last major poaching operation in the Gulf of Fernandez took place in June 2018; no Pachycephalosaurus were specifically confirmed among the captured animals.

Pachycephalosaurus has been reported in the illegal animal trade as of 2022. Poachers and illegal breeders, having likely obtained this animal’s DNA after it went open-source in 2018, have been apprehended with this animal in the United States and England. Two animals were rescued from American poachers on May 17, 2022 by the Department of Prehistoric Wildlife, while a breeding operation was broken up by DPW agents cooperating with the Metropolitan Police in Finsbury Park, London. At least one adult Pachycephalosaurus escaped from breeders during the conflict. In both cases, the animals were captured by the DPW and transported to secure facilities.

Not all captive animals are free, since illegal breeding and trafficking continues. It may be that some Pachycephalosaurus yet remain in captivity, unknown to the authorities. A major hub of this illegal trade is the Amber Clave night market in Valletta, Malta.

Wild populations

This dinosaur first evolved in North America during the Cretaceous period, with the earliest fossils dated at 70 million years ago. It seems to have inhabited forested uplands of the western part of the continent, though the poor fossil quality in the east means that any animals living there might simply not have fossilized. At the very end of the Cretaceous, a mass extinction event destroyed most of the world’s megafauna, including all Pachycephalosaurus. Genetic material persisted in fossil form for 66 million years, eventually being discovered by scientists who used genetic modification to restore the animal to life.

De-extinct animals have, since 2018, reentered the world’s ecosystems due to human intervention. Pachycephalosaurus has been transported around the world, illegally bred, and in some cases escaped captivity due to the difficulty of containing it. No wild populations have yet been reported as establishing anywhere, since this dinosaur remains rare.

Behavior and Ecology
Activity Patterns

Pachycephalosaurus is predominantly active during the day, meaning it is diurnal.

Diet and Feeding Behavior

This dinosaur is mainly herbivorous; according to Jurassic World animal behaviorists its diet consists entirely of fruits and seeds. It uses its beak to snip off pieces of food, and its incisors are useful for slashing through the meat of fruit. In the rear of its mouth it has cutting teeth to further shred its food before swallowing. InGen Pachycephalosaurus have much more extensive cheek tissue than their ancestors, which is a double-edged sword; they are less likely to drop food while eating, but cannot open their mouths as wide. They must take smaller bites. These restricted mouths also limit the types of food they can feed upon.

Illustration of Pachycephalosaurus feeding on aquatic vegetation (image from the Dinosaur Protection Group)

Paleontologists believe that the teeth of Pachycephalosaurus would have originally allowed it to eat animal meat as well as plants, making it omnivorous. It may have scavenged from carcasses. Due to their smaller gape, it would be difficult for an InGen pachy to bite off meat from a dead animal. In theory, they could still supplement their diet with eggs, though these were not provided to them in captivity. Their are known to eat lysine-rich plants such as soy on Isla Sorna, allowing them to circumvent InGen’s lysine contingency. Fossil evidence about their diet is virtually non-existent, but their teeth suggest to scientists a diet including leaves, fruit, and seeds, relatively similar to what the InGen animals eat.

In the game Jurassic World: Evolution, this dinosaur prefers to feed on cycads. They will also eat grasses and horsetails, but cannot effectively digest tree ferns, conifers, or ginkgoes. In the sequel, it is shown to feed on leafy climbers.

Social Behavior

The social lives of Pachycephalosaurus have been likened to those of the African buffalo, another curmudgeonly herd-dwelling herbivorous creature. However, a notable difference is that Pachycephalosaurus is not very intelligent, so its herds have considerably less complex behaviors. They herd together for defense, though they probably also gain a sense of familiarity from their companions; their herds appear to not be extremely large. Considering its low intelligence, it probably cannot remember very many faces.

While it is not known how rigid their social hierarchies are, Pachycephalosaurus is known to settle disputes through fighting. When two animals fight, often over something such as mating rights or access to resources, they will face one another and strike with their skulls. The head of a Pachycephalosaurus is not actually built for mutual head-on ramming, as their rounded shapes would cause them to glance off each other. Instead, they will side-swipe their domes at one another or try to ram the flank of their opponent. A successfully strong hit leaves a rival winded and reeling, and the fight is over once one animal gives up. Fighting in this way helps pachys to determine dominance over each other, but it also serves another purpose: it keeps them in shape for defending themselves against predators, who they combat using similar techniques.

Friendlier interactions are shown in Jurassic World: Evolution 2 to also involve the head. When not using them to fight, they will more gently knock their domes together without it turning into combative behavior. These more relaxed bumps are mutually engaged in, rather than one challenging another.


Breeding among this dinosaur has yet to be observed, but it is highly likely that the domed skull and its knobby ornamentation play a role in courtship. Males with worn-down head spines are more mature, giving an easy way to distinguish successful adults, and those with larger domes will be better at fighting rivals and predators. Males will engage in headbutting brawls to impress females, with mating rights going to the victor. In captivity, pachys will ram inanimate objects, but it is not known whether they use this to show off their strength in the wild.

All dinosaurs lay eggs, and since Pachycephalosaurus is a herd animal, they probably nest in groups. This would give the eggs and juveniles better protection against predators. Aside from these conclusions, not much is known about how these animals breed; the average clutch size and survival rate is unknown. Medium-sized and smaller dinosaurs typically have incubation periods lasting around three months, but in Pachycephalosaurus, the duration has not been confirmed.

Concept art of young Pachycephalosaurus by Shaun Keenan. The domes are illustrated as larger than fossil evidence would suggest for this age group.

Nearly all dinosaurs exhibit parental behavior. Many do so extensively, including the ceratopsians, which are somewhat closely related to pachycephalosaurs. The growth rate is not entirely known, but takes at least a few years. Fossil evidence suggests that juveniles, whose skull domes have not yet grown thick and resilient, do not headbutt as rigorously as adults. As they mature, their long cranial spines wear down into bumps, and their skulls stop growing as their domes reach their final size. These are signs of sexual maturity, indicating that the Pachycephalosaurus is ready to mate.

Most paleontologists believe that the smaller pachycephalosaurs Dracorex and Stygimoloch are different growth stages of Pachycephalosaurus, rather than totally different genera. The flat-headed Dracorex is thought to be a juvenile of a few months to years old, while the spiny Stygimoloch is an adolescent or young adult. While InGen has created these species separately, it may be that they have used genetic engineering to cause some Pachycephalosaurus to retain their “cute” juvenile traits into adulthood, possibly for marketing purposes.


A simple creature, Pachycephalosaurus does not have especially complicated communication and mostly grunts and snorts to its fellow animals. Its most noticeable vocalization is a loud, ringing bellow, which it uses when it is distressed. The volume and alarming tone of this cry make it easy to hear and unmistakable in meaning. Other pachys in the area will immediately know that one of their own kind has encountered a threat. Pachycephalosaurus will also make squealing, screeching, and hissing sounds when it is agitated.

Body language is also important. When it is showing aggression, it will wave its head around and paw at the ground, warning that it is ready to charge. Since this animal has distinct coloration, it probably relies strongly on visual cues.

Ecological Interactions

This dinosaur forms herd associations with Parasaurolophus, Gallimimus, and Mamenchisaurus. With the exception of Gallimimus (which is omnivorous), all of these species are herbivores. They avoid competition and live comfortably among one another through niche partitioning. None of them prefer quite the same lifestyle, and none of them feed in quite the same way, so they coexist without conflict. Pachycephalosaurus eats lower-growing plants with soft leaves and fruit, whereas Gallimimus feeds mainly from the ground and Parasaurolophus can rear up to reach higher branches. The huge sauropod Mamenchisaurus feeds from the tops of trees. These animals’ keen senses also complement one another, and the defensive capabilities of Pachycephalosaurus benefit its neighbors.

Other dinosaurs known from its habitat on Isla Sorna include Edmontosaurus, Stegosaurus and Triceratops, which it does not appear to herd with, as well as the carnivores Compsognathus and Tyrannosaurus. While the former is only threatening in very large groups, a tyrannosaur can easily kill a pachy without any struggle or risk, making this giant carnivore one of the pachy’s most threatening predators. Even some of the local herbivores may be dangerous, such as the aggressive Triceratops, which is known to harass smaller herbivores. To defend itself from predators, this dinosaur employs its head. While the skull dome originally evolved as a competitive structure that aided males in courting females, it also works quite well against other species. A predator the size of Velociraptor, which is believed to have hunted this animal from time to time on Isla Sorna, could be seriously injured by a strike from a pachy head.

Its relationships on Isla Nublar were not as well understood, but in the wild, it inhabited mountainous foothills alongside the tiny herbivore Microceratus. There is also a possibility it encountered Sinoceratops with some frequency, since this ceratopsian was heard using an aggression cry that sounds very much like that of Pachycephalosaurus. Before its extinction in early 2018, the predator Metriacanthosaurus inhabited northern forests, and may have preyed upon pachys. A large number of other animals lived in the north before they were all killed off in the summer of 2018, but since Pachycephalosaurus became quite rare on Isla Nublar, little is known of its ecological relations on that island.

A habitual frugivore, this dinosaur could benefit many species of plants in its habitat by spreading their seeds. By feeding on various fruits throughout its habitat range, a Pachycephalosaurus would end up distributing seeds far and wide in its dung, depositing them in ready-made fertilizer. The shrubs and trees it feeds from likely become common in its habitat over time. Other plants, however, have their leaves and seeds eaten by this dinosaur, which would harm them. The specific plants it feeds upon are not known, but it has been seen near coniferous and palm forest.

It also hosts a large microbiome, as most animals do, including species both beneficial and harmful. Opportunistic pathogens living on its scaly skin can infect surface wounds, weakening the dinosaur. Pachycephalosaurus is susceptible to the disease bumblefoot, in which an infected foot wound is healed over and develops into a swollen mass. This can make its movements more cumbersome, and in addition, the smell of the festering wound under the skin can draw the attention of carnivores. Because of this, bacteria that would normally be harmless can unexpectedly lead to its death. Fossils also show wounds to its skull becoming diseased; some fossil skulls show signs of osteomyelitis, or infection of the bone. This can occur after fights. Macroscopic pests such as mosquitoes will also bite it. According to the game Jurassic World: Evolution, it is also host to the bacterium Campylobacter, which can cause the disease campylobacteriosis.

Cultural Significance

This dinosaur has long been known as the archetype of pachycephalosaurs, despite its confusing early taxonomic history. Popularly called the “bonehead” for its thick skull, it is famous for its powerful ramming ability and low intelligence. Both scientists and laypeople have compared it to a bighorn sheep, assuming that its head meant it would clash heads with rival males, but a more modern understanding suggests that they would not have been able to hit head-on. In art, it is almost universally shown in combat. Pachycephalosaurus is thought of as aggressive and stubborn, and so it comes to symbolize anger, impulsiveness, and ignorance. Recent studies suggesting it may have been able to eat meat as well as plants have further enhanced the monster-like reputation of this dinosaur. Among all the herbivores (and mostly-herbivores), few dinosaurs are more demonized than the thick-skulled, hair-trigger Pachycephalosaurus.

Some people have compared pachycephalosaurs’ appearance to that of elderly people, being that they stand upright but hunched, have human-like five-fingered hands, and appear bald. In many cultures old people are known for their stubbornness, another stereotype they share with this short-tempered dinosaur.

In Captivity

Although InGen had plans to exhibit this animal in the 1990s, it was never successfully integrated into Jurassic Park (at either the Isla Nublar or San Diego locations), and details about its exhibits there are not specifically known. It was not until the 2000s that living Pachycephalosaurus made it into public view. At Jurassic World, these creatures were put on display in an attraction called the Pachy Arena. Located near Main Street, this enclosure contained target objects that the dinosaurs could ram, showing off their strength for visitors. The name of the attraction, as well as some of its descriptions, imply that the Pachycephalosaurus would sometimes engage in headbutting contests with each other in the arena too. This is a natural behavior, but can be stressful for the animals and could lead to injury. Encouraging it for the entertainment of guests is ethically dubious at best. After the closure of Jurassic World in late 2015, the Pachy Arena was specifically criticized by the Dinosaur Protection Group.

A Pachy being sedated by the ACU
Escaped animal being sedated, Isla Nublar (12/22/2015)

While not performing, the pachys were housed elsewhere in the park. They appear to have inhabited the west side of the central valley, where three other attractions existed: the Gyrosphere, Gallimimus Valley, and Triceratops Territory. Pachys do not seem to have lived in the Gyrosphere area, but may have inhabited one of the other two. They are known to have herded with Gallimimus in the wild, so they would have been comfortable here. When in their living space, they would still practice their headbutting attacks among each other, and fight for dominance or mating rights. This posed a regular problem for Jurassic World’s security staff, since the shock would disrupt the contestants’ RFID tracking implants. When these chips shorted out, the animals were no longer constrained by the park’s invisible fence system, and they could roam into areas of the island such as the West Plains where they were not supposed to be. It also made it impossible to track the animal by GPS. When this happened, staff would have to locate and tranquilize them, repair or replace the damaged RFID chip, and return the escapee to its habitat.

There are challenges to keeping Pachycephalosaurus in captivity, as demonstrated in Jurassic World. It is a reactive and moody creature, but it does have one clear advantage: it is not very smart. Easily chased down should it escape, and outwitted if its attempt is caught in time, Pachycephalosaurus poses little threat to a well-prepared park security team. Keeping it satisfied is also fairly easy, since unintelligent animals are more easily entertained in general. Pachys enjoy using their heads in play, so they should be given sturdy things they can ram. In Jurassic World, this was accomplished using sandbags and other objects. Their heads and necks are designed for taking impacts, but remember that they did not originally evolve alongside modern materials such as concrete and metal. Pachys should be provided with safer targets and kept entertained so that they do not begin ramming things they may injure themselves on.


This was not only one of the first pachycephalosaurs known to paleontologists, but also the first to be subject to de-extinction in the late twentieth century. A substantial amount of genetic research had to go into bringing this animal back to life, including sequencing its genome and determining compatible donors to replace missing segments. Once it was alive, its biology could be studied in new ways. Historically, one of the questions surrounding pachycephalosaurs was their ontogeny; the related Dracorex and Stygimoloch are now thought to probably be the same species as Pachycephalosaurus, but at different stages of growth. InGen has recreated them separately, raising questions about the identities of these animals that have yet to be answered. In paleontological history, Pachycephalosaurus itself took a good many decades to be truly understood. When they were first found, pachycephalosaurs and troodontids were thought to have been the same type of animal, due to the fragmentary nature of their remains.


In Jurassic World, the Pachy Arena was a popular attraction in which visitors could see Pachycephalosaurus butting heads and ramming targets. After the park closed, however, the Dinosaur Protection Group made controversial commentary about the attraction, criticizing it for using the dinosaurs’ fighting behavior for entertainment.

Male Pachycephalosaurus being captured for Jurassic Park: San Diego

At the same time, Pachycephalosaurus was involved in the debate as to whether or not de-extinct animals had the right to exist at all. The volcano Mount Sibo was becoming active in 2017, leading to the possibility that Isla Nublar’s ecosystem could be completely destroyed. Pachycephalosaurus was among the most at-risk dinosaurs since its habitat lay in the foothills of the volcanic mountain, exposing it to all kinds of hazards. Debate raged in the United States and abroad; while many people argued that the dinosaurs deserved not to suffer and die, many more in positions of power were opposed to helping them. The argument was that these organisms were corporate products, not natural animals, and that it was the responsibility of their owners to care for them. This argument went back all the way to when people outside of InGen first began learning about dinosaurs; Pachycephalosaurus had been around then too, and was involved in the early conflicts surrounding de-extinct animal rights. In the end, Mount Sibo erupted after the U.S. government declared no federal responsibility, and Masrani Global cited high costs as reason not to intervene. Pachycephalosaurus has likely become extinct on Isla Nublar because of corporate and government inaction. If any survived by being transplanted to the mainland, they are now subject to a wider range of animal rights and ecological debates.


The original reason Pachycephalosaurus was cloned was for entertainment. At the time, its creator International Genetic Technologies was planning for a de-extinction theme park which would exhibit various Mesozoic life forms for tourists, and a species like Pachycephalosaurus would make a valuable addition. While this dinosaur’s public debut was delayed by many years due to difficulties surrounding the park, it had already contributed significantly to genetic research by being the first pachycephalosaur subject to the de-extinction process. It was one of the earliest additions to InGen’s genetic library, being among a handful of species cloned between 1983 and 1993. Ecologically, it is useful as a distributor of seeds when it eats fruit, helping plants to germinate and spread.

Pachycephalosaurus in charging posture

It was exhibited during the 2000s and 2010s, though its attraction was not one of the most famous draws to Jurassic World. Despite being a simple-minded animal, it proved capable of being trained to respond to basic commands, especially those that encouraged its aggressive fighting behaviors (this is considered controversial as it stresses the animals and can cause injury). During its time in the park, Pachycephalosaurus was studied by geneticists, animal behaviorists, and paleoveterinarians, all of whom learned valuable new information about its biology. At least one variety of artificially-engineered hybrid animal designed by InGen’s Dr. Henry Wu is believed to have incorporated Pachycephalosaurus genes.

Though it is no longer exhibited to the public due to Jurassic World’s closure, it may still have value to people. All de-extinct animals have unique biological properties when compared to modern life, and the genetic engineering processes inherent to their recreation further alter their biology and essentially make them entirely new creatures. The exact biopharmaceutical uses for Pachycephalosaurus have not been explored, but one can imagine the highly unusual and fast-healing type of bone found in its skull dome could be medically valuable. It is trainable, but due to its tendency to ram things that annoy it, this dinosaur probably would not make for a good companion. Instead it is best left in the wild, or in zoological facilities capable of supporting it.


Generally, Pachycephalosaurus would rather avoid danger, but it is a very reactive animal and is fully capable of defending itself from a human-sized threat. You stand on two legs, like most of its theropod predators, so there is a chance that this unintelligent dinosaur may think of you as a potential attacker. This goes double if you do anything to provoke it, such as harassing the dinosaur or its family group or making sounds that it could mistake for a challenge. If you see one, keep a good distance, since it can run fairly fast. When it is preparing to charge, a pachy will paw at the ground and growl or hiss, warning you to back off. Should you fail to do this, it will run headlong at you, intending to strike and incapacitate. If it lowers its head, get ready to dodge and find shelter. Hide somewhere very sturdy, as it can ram through most barriers, or climb a tree where it cannot follow you. If you are in a vehicle, stay toward the center, away from doors and windows. Its ramming attack can damage most vehicles and could shatter glass.

Pachycephalosaurus ramming a vehicle in self-defense, Isla Sorna (5/28/1997)

When it strikes something, it will take a moment to recover and get its bearings. This will give you a window of opportunity to get away, but running is only an ideal option if shelter is within reach or your stamina is very, very good. Instead of fleeing in a panic, which might provoke it further, back down and act submissive, trying to convince it that the fight is won. However, if it is still aggressive and attacks again, you may need to try and shield yourself. Use an arm or any object on your person to protect your head and chest, or turn aside to sustain a glancing blow instead of a full collision. In many cases, pachycephalosaurs will retreat after knocking down an enemy, so if it hits you, stay down until it leaves. After it has gone, get any wounds treated; the horns of this dinosaur can cause lacerations and its ramming attacks may bruise muscles and organs or even break bones. The most preferable way to encounter a Pachycephalosaurus is at enough distance that it does not feel threatened by you in the first place. Avoid making sudden movements or loud sounds that could agitate it. Remember that it is not very smart, and so your actions should leave no room for interpretation. If it does not think you are a danger, it will remain peaceful, and you can be on your way without any trouble.

Behind the Scenes

It was originally suggested that the pachycephalosaurs created by InGen had undergone some changes, based on the amount of smaller specimens seen in The Lost World: Jurassic Park. This seemed to warrant a new taxonomic subspecies, Pachycephalosaurus wyomingensis vegrandis,” but more accurate paleontological research in recent times have proven such assignment unnecessary and incorrect. As it turned out, the pachycephalosaurs in the film were the correct size, according to the Making of Book animatronic picture seen here and here. A size comparison was also done of animals in the round-up sequence, seen here.

When this animal made a cameo appearance in 2015’s Jurassic World, it briefly became the subject of a bizarre case of manufactured outrage. Shortly after the film was released, conservative news blogs began reporting that “liberals” were offended by the dinosaur’s nickname, “pachy,” because it sounds phonetically similar to a racial slur used against people from Pakistan. Supposed film quotes that people were allegedly offended by were even fabricated for these news stories (e.g., “Those pachys are out of control,” a line of dialogue that does not occur in the film, and was never in any known version of the script). Since fans and general audiences universally understood the dinosaur’s nickname to be derived from its genus name, no one had actually assumed Pachycephalosaurus to be an allegory for any racial group, especially as it appears in the film for mere seconds. With no actual backlash against the dinosaur, the reactionary counter-backlash had little means to stay relevant, and died out within a few days.

In later installments of the film series, Pachycephalosaurus was replaced by Stygimoloch, which in real life is a junior synonym of Pachycephalosaurus. Paleontologists believe them to be two different stages of growth for the same animal. According to the franchise’s science advisor Jack Horner, someone on the design team for Jurassic World: Fallen Kingdom had their heart set on portraying Stygimoloch as a legitimate genus in spite of Horner’s protests.

Disambiguation Links

Pachycephalosaurus wyomingensis (C/N)

Pachycephalosaurus wyomingensis (JN)

Pachycephalosaurus wyomingensis (L/M)

Pachycephalosaurus wyomingensis “gigas” (IDW-JPR)

Pachycephalosaurus wyomingensis “gigas” (CB-Topps)