That is a Pachycephalosaurus. These creatures literately invented the term "thick-headed​".
— Allen, describing Pachycephalosaurus

Pachycephalosaurus (name meaning "Thick-Headed Lizard"), often nicknamed Pachy for short, is a genus of herbivorous pachycephalosaurid dinosaur that originated during the Late Cretaceous period of what is now North America. Measuring around 5 meters long and identifiable by its thick domed skull, it is one of the world's most recognizable dinosaurs.

In the episode "Fall of a Kingdom Part II: The Return of the King", a group of ten Pachycephalosaurus were brought back to the park from Late Cretaceous Montana of 65 million years ago. The team also brought some of their eggs so they can incubate them so they can hatch.   

Facts Edit

Era & DiscoveryEdit

Pachycephalosaurus lived in western North America during the Late Cretaceous period, from 77–65 million years ago. Therefore, it died out with the other dinosaurs at the end of the Cretaceous. It shared its environment with other dinosaurs like the hadrosaurs, ceratopsians, and ankylosaurus as well as the Raptors and tyrannosaurs that saw it as prey.

Pachycephalosaurus remains were first discovered in the early 1850s but the dinosaur itself was not named until 1931 by Charles W. Gilmore. Remains have been excavated in Montana, South Dakota, and Wyoming. Pachycephalosaurus has also become one of the most well-known dinosaurs in the world.

Physical AttributesEdit

Pachycephalosaurus is the largest known pachycephalosaur, growing to be about 6 – 7 feet (2 – 2.2 m) tall, measured 15 – 17 feet (4.6 – 5.2 m) long, and weighed around 1 ton (2,000 lbs.) It also possessed long legs and small forearms. Its head was equipped with a small beak, round eyes, and most notably an extremely thick, domed skull roof.

The thick, well over 9-inch skull domes of Pachycephalosaurus was used in infraspecific combat, for example, bashing heads during the mating season, just like the modern ibex do. It is also likely that the animals butted their heads against each other's flanks during the mating season, not unlike giraffes do today. Given the chance, it is also possible they used their heads to defend themselves against predators. Additionally, the head of Pachycephalosaurus is strong enough to burst through a concrete wall.

Behavior & TraitsEdit

Pachycephalosaurus lived in small herds of around, at maximum, six other individuals in a single herd. Like many herbivores, Pachycephalosaurus often separated while feeding, which often gave predators and advantage to attack.

Pachycephalosaurus was generally a highly curious creature, known to follow interesting other animals like humans around and to investigate other things of interest. However, when dealing with its own kind, Pachycephalosaurus could be highly aggressive, attacking other Pachycephalosaurus (or at least what it thought to be them) with a powerful headbutt. Pachycephalosaurus also didn't seem to be highly intelligent, as it could mistake its own reflection for another Pachycephalosaurus.

Much like the larger ceratopsians, Pachycephalosaurus jousted with each other. The young did it for fun, but the adults fought for dominance. With their heads measuring more than 9 inches thick (therefore, making them in comparison to a battering ram) and their spines built to withstand the impact of the hit, it would be very painful to get hit by a Pachycephalosaurus.

Journal Entry Edit

Distinctive for the reinforced domed skull that they use to fight by head-butting, Pachycephalosaurus lived in North America. They are one of the last non-avian dinosaurs before the Cretaceous-Paleogene extinction event about 65 million years ago.

Like many herbivores, Pachycephalosaurus uses its large, round-domed head with elaborate spikes around the skull when it comes to defense. With a skull over 10 inches thick and long powerful back legs, it can ram head-first into enemies with tremendous force.

They are among the fastest dinosaurs, easily able to sprint over long distances. A high metabolic rate gives them incredible stamina and a real thrust. Pachys normally stick to the redwood forests where they are less exposed, this has led them to favor the plants growing below.

— Allen, in his Journal, about Pachycephalosaurus



  • Pachycephalosaurus is the largest member of its family to be brought to the park.
  • The sound effects of Pachycephalosaurus are that of bull and horse sound effects.
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