Total anky death
Extinct as can be!

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Temporal range: Late Cretaceous
An artist's illustration of Pachycephalosaurs wyomingensis
Scientific classification
Kingdom: Animalia
Phylum: Chordata
clade: Dinosauria
Order: Ornithischia
Family: Pachycephalosauridae
Tribe: †Pachycephalosaurini
Genus: Pachycephalosaurus
Brown & Schlaikjer, 1943
Species: P. wyomingensis

P. spinifer?

Binomial name
Pachycephalosaurs wyomingensis
Gilmore, 1931

Pachycephalosaurus is an extinct genus of pachycephalosaurid dinosaurs. It lived during the late Cretaceous period in what is now North America from 68 to 66 million years ago in the Maastrichtian era. The type species is named P. wyomingensis.

History of discovery[]

Remains attributable to Pachycephalosaurus may have been found as early as the 1850s. As determined by Donald Baird, in 1859 or 1860 Ferdinand Vandeveer Hayden, an early fossil collector in the North American West, collected a bone fragment in the vicinity of the head of the Missouri River, from what is now known to be the Lance Formation in southeastern Montana. This specimen, now ANSP 8568, was described by Joseph Leidy in 1872 as belonging to the dermal armor of a reptile or an armadillo-like animal. It became known as Tylosteus.

Its actual nature was not found until Baird restudied it over a century later and identified it as a squamosal (bone from the back of the skull) of Pachycephalosaurus, including a set of bony knobs corresponding to those found on other specimens of Pachycephalosaurus. Because the name Tylosteus predates Pachycephalosaurus, according to the International Code of Zoological Nomenclature Tylosteus would normally be preferred. In 1985, Baird successfully petitioned to have Pachycephalosaurus used instead of Tylosteus because the latter name had not been used for over fifty years, was based on undiagnostic materials, and had poor geographic and stratigraphic information.

This may not be the end of the story; Robert Sullivan suggested in 2006 that ANSP 8568 is more like the corresponding bone of Dracorex than that of Pachycephalosaurus. The issue is of uncertain importance, though, if Dracorex actually represents a juvenile Pachycephalosaurus, as has been recently proposed.

P. wyomingensis, the type and currently only valid species of Pachycephalosaurus, was named by Charles W. Gilmore in 1931. He coined it for the partial skull USNM 12031, from the Lance Formation of Niobrara County, Wyoming. Gilmore assigned his new species to Troodon as T. wyomingensis. At the time, paleontologists thought that Troodon, then known only from teeth, was the same as Stegoceras, which had similar teeth. Accordingly, what are now known as pachycephalosaurids were assigned to the family Troodontidae, a misconception not corrected until 1945, by Charles M. Sternberg.

In 1943, Barnum Brown and Erich Maren Schlaikjer, with newer, more complete material, established the genus Pachycephalosaurus. They named two species: Pachycephalosaurus grangeri, the type species of the genus Pachycephalosaurus, and Pachycephalosaurus reinheimeri. P. grangeri was based on AMNH 1696, a nearly complete skull from the Hell Creek Formation of Ekalaka, Carter County, Montana. P. reinheimeri was based on what is now DMNS 469, a dome and a few associated elements from the Lance Formation of Corson County, South Dakota.

They also referred the older species "Troodon" wyomingensis to their new genus. Their two newer species have been considered synonymous with P. wyomingensis since 1983.

In 2015, some pachycephalosaurid material and a domed parietal attributable to Pachycephalosaurus were discovered in Scollard Formation, Alberta, Canada, implying dinosaurs of this era were cosmopolitan and didn't have discrete faunal provinces.


Pachycephalosaurus skull

A cast of the only Pachycephalosaurus skull

Pachycephalosaurus was probably bipedal and was the largest known of the bone-headed dinosaurs, with some others being Stygimoloch, Dracorex, and Stegoceras. It is famous for having a large, bony dome atop its skull, up to 25 centimeters (10 inches) thick, which safely cushioned its brain. The dome's rear aspect was edged with bony knobs and short bony spikes were projected upwards from the snout. These features suggest that, despite their bipedal stance, they were likely to have been relatives of the ceratopsians possibly branching from early individuals of the group.

Using data from other pachycephalosaurids, it has been estimated that Pachycephalosaurus was approximately the length of a large car, maybe around 4.6m long (15 feet) and had a fairly short, thick neck, short fore limbs, a bulky body, long hind legs and a heavy tail, which was likely to have been held rigid by ossified tendons. Large eye-sockets that faced forward suggest that the animal had good vision and was capable of binocular vision.


Pachycephalosaurus scale

Estimated scale between a Pachycephalosaurus adult and a human

Scientists once suspected that Pachycephalosaurus and its dome-headed relatives were the bipedal equivalents of the big-horned sheep of today. It was thought that, in the mating season, big males would run at one another, clashing heads to decide which would dominate and mate with a herd of females. It was also thought that they might have used their domed heads for defense against predators. However, it is now believed that the Pachycephalosaurs would not have used their domes in this way so much.

Pachycephalosaurus skull

Adult skull in two perspectives

The adult head bones could not adequately have withstood pressure and impact and the skulls lacked proper shock absorption like Big Horned Sheep, and it's more likely that they head-butted their sides, to try to knock them off balance. Also, there is no evidence of scars or other damage on fossilized Pachycephalosaurus skulls possibly caused by head-butting. On the other hand, it's unlikely that pachycephalosaurs developed those thick skulls for display alone. It's a rather opinionated discussion.

Scientists do not yet know what these dinosaurs ate. Having very small, ridged teeth they could not have chewed tough, fibrous plants as effectively as other dinosaurs of the same period. It is assumed that pachycephalosaurs lived on a mixed diet of leaves, seeds, fruit and insects. The sharp, serrated teeth would have been very effective for shredding plants such as ferns. The diet of insects is a debatable one however, some say that Pachycephalosaurus was a true carnivore, while some explain how this animal might've been a well omnivore.


It is believe that Pachycephalosaurus lived in woods, forests, feilds, meadows, lowlands, grasslands and plains of Montana, North Dakota, South Dakota, Wyoming and Alberta during the Late Cretaceous and little bit in the Early Paleogene. The dinosaurs it shared these locations with can be found in many of the same locations that Pachycephalosaurus inhabited. The floodplains that Pachycephalosaurus lived in had trees, grass, shrubs, ferns, woodlands, ponds, streams, rivers, brooks, creeks and valleys.

Lance Formation[]

Was a plain filled with streams forest and woods the formation was named after Lance Creek and located in Wyoming. The Lance Formation was one of the many places that Pachycephalosaurus called home. The area had plains with trees, meadows, swamps, steams, creeks, brooks, ponds, ferns, shrubs and wooded areas but it was mostly believed to be a wetland floodplain. Pachycephalosaurus not only lived alongside dinosaurs in the Lace Formation but it shared the area with birds, reptiles like lizards, crocodiles, alligators, snakes, turtles, alongside amphibians like, frogs, salamanders and toads, also invertebrates like, arachnids, insects, arthropods, crustaceans, fish and small mammals. Pachycephalosaurus individuals have been found elsewhere other than Lance Formation.

Scollard Formation[]

Was a plain located near Scollard Canyon the formation is named after the canyon in Alberta, Canada. Scollard Formation was one of the many places that Pachycephalosaurus made it's home like other habitats that the dinosaur lived in this location was believed to be a floodplain at one point with forests, meadows, fields, brooks, ponds, creeks, ferns, grass, trees, shrubs and woods located in the plains. Pachycephalosaurus has also been found alongside next to the Scollard Canyon. Animals like, birds, fish, amphibians like, frogs, toads, salamanders, birds, reptiles like, snakes, lizards, turtles, alligators, crocodiles, invertebrates like, insects, arachnids, crustaceans, arthropods, and small mammals lived in plains of Scollard at the sametime with Pachycephalosaurus and other dinosaurs.


Pachycephalosaurus gives its name to the Pachycephalosauria, a clade of herbivorous ornithischian ("bird hipped") dinosaurs which lived during the Late Cretaceous Period in North America and Asia. Despite their bipedal stance, they were likely more closely related to the ceratopsians than the ornithopods.

Pachycephalosaurus is the most famous member of the Pachycephalosauria (though not the best-preserved member). The clade also includes Stenopelix, Wannanosaurus, Goyocephale, Stegoceras, Homalocephale, Tylocephale, Sphaerotholus and Prenocephale. Within the tribe Pachycephalosaurini, Pachycephalosaurus is most closely related to Alaskacephale. Dracorex and Stygimoloch have been synonymized with Pachycephalosaurus. Debates and arguments of how Dracorex or Stygimoloch may have been a juvenile of Pachycephalosaurus are still ongoing.



Dracorex and Stygimoloch were first proposed to be juvenile or female morphologies of Pachycephalosaurus at the 2007 annual meeting of the Society of Vertebrate Paleontology. Jack Horner of Montana State University presented evidence, from analysis of the skull of the single existing Dracorex specimen, that this dinosaur may well be a juvenile form of Stygimoloch. In addition, he presented data that indicates that both Stygimoloch and Dracorex may be juvenile forms of Pachycephalosaurus. Horner and M.B. Goodwin published their findings in 2009, showing that the spike/node and skull dome bones of all three "species" exhibit extreme plasticity and that both Dracorex and Stygimoloch are known only from juvenile specimens while Pachycephalosaurus is known only from adult specimens.

These observations, in addition to the fact that all three forms lived in the same time and place, led them to conclude that Dracorex and Stygimoloch were simply juvenile Pachycephalosaurus, which lost spikes and grew domes as they aged. A 2010 study by Nick Longrich and colleagues also supported the hypothesis that all flat-skulled pachycephalosaur species were juveniles of the dome-headed adults, such as Goyocephale and Homalocephale.

The discovery of baby skulls assigned to Pachycephalosaurus that were described in 2016 from two different bone beds in the Hell Creek Formation has been presented as further evidence for this hypothesis. The fossils, as described by David Evans and Mark Goodwin et al are identical to all three supposed genera in the placement of the rugose knobs on their skulls, and the unique features of Stygimoloch and Dracorex are thus instead morphologically consistent features on a Pachycephalosaurus growth curve.

Dome function[]

It has been commonly hypothesized that Pachycephalosaurus and its relatives were the bipedal equivalents of bighorn sheep or musk oxen, where male individuals would ram each other headlong, and that they would horizontally straighten their head, neck, and body in order to transmit stress during ramming. However, there have also been alternative suggestions that the pachycephalosaurs could not have used their domes in this way.

The primary argument that has been raised against head-butting is that the skull roof may not have adequately sustained impact associated with ramming, as well as a lack of definitive evidence of scars or other damage on fossilized Pachycephalosaurus skulls (however, more recent analyses have uncovered such damage; see below). Furthermore, the cervical and anterior dorsal vertebrae show that the neck was carried in an "S"- or "U"-shaped curve, rather than a straight orientation, and thus unfit for transmitting stress from direct head-butting. Lastly, the rounded shape of the skull would lessen the contacted surface area during head-butting, resulting in glancing blows.

Alternatively, Pachycephalosaurus and other pachycephalosaurid genera may have engaged in flank-butting during intraspecific combat. In this scenario, an individual may have stood roughly parallel or faced a rival directly, using intimidation displays to cow its rival. If intimidation failed, the Pachycephalosaurus would bend its head downward and to the side, striking the rival pachycephalosaur on its flank. This hypothesis is supported by the relatively broad torso of most pachycephalosaurs, which would have protected vital organs from trauma. The flank-butting theory was first proposed by Sues in 1978, and expanded upon by Ken Carpenter in 1997.

In 2012, a study showed that cranial pathologies in a P. wyomingensis specimen were likely due to agonistic behavior. It was also proposed that similar damage in other pachycephalosaur specimens previously explained as taphonomic artifacts and bone absorptions may instead have been due to such behavior. Peterson et al. (2013) studied cranial pathologies among the Pachycephalosauridae and found that 22% of all domes examined had lesions that are consistent with osteomyelitis, an infection of the bone resulting from penetrating trauma, or trauma to the tissue overlying the skull leading to an infection of the bone tissue. This high rate of pathology lends more support to the hypothesis that pachycephalosaurid domes were employed in intra-specific combat.

Pachycephalosaurus wyomingensis specimen BMR P2001.4.5 was observed to have 23 lesions in its frontal bone and P. wyomingensis specimen DMNS 469 was observed to have 5 lesions. The frequency of trauma was comparable across the different genera in the pachycephalosaurid family, despite the fact that these genera vary with respect to the size and architecture of their domes, and fact that they existed during varying geologic periods. These findings were in stark contrast with the results from analysis of the relatively flat-headed pachycephalosaurids, where there was an absence of pathology. This would support the hypothesis that these individuals represent either females or juveniles, where intra-specific combat behavior is not expected.

Histological examination reveals that pachycephalosaurid domes are composed of a unique form of fibrolamellar bone which contains fibroblasts that play a critical role in wound healing, and are capable of rapidly depositing bone during remodeling. Peterson et al. (2013) concluded that taken together, the frequency of lesion distribution and the bone structure of frontoparietal domes, lends strong support to the hypothesis that pachycephalosaurids used their unique cranial structures for agonistic behavior. CT scan comparisons of the skulls of Stegoceras validum, Prenocephale prenes, and several head-striking artiodactyls have also supported pachycephalosaurids as being well-equipped for head-butting. New studies reveal that Pachycephalosaurus and other Pachycephalosaurids may have actually rammed the sides of each other instead, rather than going head-on.


Scientists do not yet know what these dinosaurs ate. Having very small, ridged teeth, they could not have chewed tough, fibrous plants as effectively as other dinosaurs of the same period. It is assumed that pachycephalosaurs lived on a mixed diet of leaves, seeds, and fruits. The sharp, serrated teeth would have been very effective for shredding plants. It is also suspected that the dinosaur may have included meat in its diet. The most complete fossil jaw shows that it had serrated blade-like front teeth, reminiscent of those of carnivorous theropods. For now, it's safe to assume that the Pachycephalosaurus likely ate assorted plants like moss, ferns, seeds, and fruits. There are discussions about this particular dinosaur could potentially be Omnivorous.


Nearly all Pachycephalosaurus fossils have been recovered from the Lance Formation and Hell Creek Formation of the western United States. Pachycephalosaurus possibly coexisted alongside additional pachycephalosaur species of the genera Sphaerotholus, as well as Dracorex and Stygimoloch, though these last two genera may represent juveniles of Pachycephalosaurus itself. Other dinosaurs that shared its time and place include Thescelosaurus, the hadrosaurid Edmontosaurus and a possible species of Parasaurolophus, ceratopsids like Triceratops, Torosaurus, and Leptoceratops, ankylosaurid Ankylosaurus, nodosaurids Denversaurus and Edmontonia, and the theropods Acheroraptor, Dakotaraptor, Ornithomimus, Struthiomimus, Anzu, Leptorhynchos, Pectinodon, Paronychodon, Richardoestesia, and Tyrannosaurus.

In the Media[]


The Lost World: Jurassic Park Pachycephalosaurus

  • Pachycephalosaurus appeared in the 1997 film The Lost World: Jurassic Park stampeding with the other dinosaurs. One of them appeared in the 2015 film Jurassic World & was tranquilized to sleep after escaping it's enclosure. It has been revealed that there are surviving populations of Pachycephalosaurus on Isla Nublar, but none were seen being evacuated from the island aboard the S.S Arcadia in the 2018 film, Jurassic World: Fallen Kingdom but its sound was heard when the poison gas is leaking before all the dinosaurs escape into the mainland. In the 2022 film, Jurassic World: Dominion, it was theorized that the Pachycephalosaurus as well as other Jurassic Park originals may make a debut themselves.
  • Pachycephalosaurus also had some roles in the Land Before Time franchise, where they are depicted as secondary villains. A trio of Pachycephalosaurus attack Cera in The Land Before Time, but they make their return in The Land Before Time IV: Journey Through the Mists when a pair of them fight each other and Petrie gets dizzy to see them fighting. However in the later movies they were one of the dinosaurs living in the Great Valley.

Primeval: New World Pachycephalosaurus

  • Pachycephalosaurus appeared in the 35th episode of Dink, the Little Dinosaur and one of them was a new but minor character and Allie named Nobbie.
  • Pachycephalosaurus made some appearances in DinoRiders.
  • A Dinosaucer Pachycephalosaurus named Bonehead appears in Various episodes of Dinosaucers, Bonehead can sometimes Devolve into his ancestral appearance.
  • Pachycephalosaurus made some appearances in Cadillacs & Dinosaurs. "Both Some Comic Books & only episode 12 nicknamed a bonehead".
  • A Pachycephalosaurus was seen briefly along with different species of Dinosaurs from the Cretaceous Period in the 3rd episode of the PBS Program The Dinosaurs! “The Nature of the Beast”.
  • Some Pachycephalosaurus appeared in a few episodes of Kong: The Animated Series. One of them was also seen briefly on the Film Kong Return to the Jungle.
  • Pachycephalosaurus is the title of a song on a 2006 album by the band Showbread, entitled Age of Reptiles. However, despite its name, the song itself doesn't have something to do with the dinosaur.
  • The Transformers characters of Hardhead and Dinotron turned into Pachycephalosaurus.
  • A Zord in Power Rangers: Dino Thunder was based on Pachycephalosaurus, and another in Power Rangers: Dino Charge.
  • Pachycephalosaurus made a few appearances in the video game Jurassic The Hunted. "Both dead & alive. The PS2 version featured only the living Pachys Stampeding to get away from Spike the Spinosaurus.
Jurassic world pachycephalosaurus by sideswipe217-d8qhkv9

Jurassic World Pachycephalosaurus

  • Pachycephalosaurus was featured in a PS3 Game Wonderbook: Walking With Dinosaurs. Staring The 2 Notable individuals Ficus & Lily in the 2 part Final Chapter Level King of Dragons.
  • Pachycephalosaurus also appeared in a couple Dinosaur Arcade Games The Lost World Jurassic Park & Savage Quest.
  • It is a huntable species in Carnivores.
  • Pachycephalosaurus was seen at the beginning of the PBS Nova Documentary Arctic Dinosaurs.
  • A juvenile Pachycephalosaurus is seen chased by two Juvenile T.Rexes & another hunted by a pair of Troodon in Dinosaur Revolution (Dinotasia). It is the model of the scrapped Prenocephale.
  • Pachycephalosaurus appears in Two National Geographic Documentaries Bizarre Dinosaurs & in Dinosaurs Decoded, where Jack Horner talks about how Stygimoloch and Dracorex are actually young Pachycephalosaurus, however, not many people agree with this, and the idea has mostly been rid of.
  • Pachycephalosaurus appeared in Dinosaur Train in season 2. Featuring the 2 Siblings Patrick & Pamela Pachycephalosaurus in the Episode Dome Headed Dinosaur.
  • Pachycephalosaurus will be in the upcoming game Saurian as a playable dinosaur.
  • In Dinozaurs There's a character named Dino Pachy his dinosaur form is a Pachycephalosaurus and his Dino Weapon mode is the Pachy Spike Sword.
  • A Pachycephalosaurus appeared in a few episodes of Dinosaur King. It was also one of the Secret Dinosaurs with tremendous powers.
  • In Pokemon series, Cranidos and its evolved form Rampardos are based on Pachycephalosaurus. These two Pokemon were first introduced in the video games, Pokemon Diamond & Pearl.
  • Pachycephalosaurus appears in Anime film Age of the Great Dinosaurs with one being the victim of the one-eyed Tyrannosaurus rex.
  • It was also in the 1994 Japanese film Tyranno's Claw.
  • The Pachycephalosaurus is one of the many creatures you can tame in the survival game Ark: Survival Evolved.
  • Pachycephalosaurus makes an appearance in the mobile game, Jurassic World: Alive as an Epic Resilient creature. It can be fused to create the Smilocephalosaurus, hybrid of the Pachycephalosaurus and the Smilodon.
  • Pachycephalosaurus appeared in the 2019 Disney show “Gigantosaurus (TV series)” as a character named Patchy who’s a friend of the 4 Dino kids Mazu, Rocky, Tiny & Bill.
    Prehistoric Planet II Pachycephalosaurus headbutting

    A Pachycephalosaurus head-butting another Pachycephalosaurus in Prehistoric Planet season 2 in the episode "Swamps"

  • Pachycephalosaurus appeared in Prehistoric Planet II in the episode Swamps.



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