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This article is about the Pachycephalosaurus species, not the Pachycephalosaur family group.

Pachycephalosaurus was a herbivorous species of dinosaur from the Late Cretaceous, notable for its thick domed skull.


Pachycephalosaurus was a bipedal creature which grew to be about five feet tall and seven feet long, and had long legs and small forearms. Its head was equipped with a small beak, round eyes, and most notably a very thick, domed skull roof. Helen Cutter claimed that Pachycephalosaurus' skull roof was only used for display, (Extinction Event) but one Pachycephalosaurus specimen was shown to use its skull roof for headbutting opponents. (Truth)

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Pachycephalosaurus vision. (Truth)

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. (Truth)

Incursions and encounters

Extinction Event

In the Cretaceous, Helen Cutter, Jenny Lewis, and the men assigned to help them, watched as a Pachycephalosaurus was hunted, killed and eaten by a male Tyrannosaurus rex. According to Helen, Pachycephalosaurus used its domed forehead for display rather than head-butting.


A Pachycephalosaurus came through an Anomaly to Vancouver in the present day and began investigating the area. It headbutted and smashed numerous windows and other reflective glass surfaces throughout the area when it mistook its reflection in them for another, rival Pachycephalosaurus.


A Pachycephalosaurus mistakes its reflection for a rival. (Truth)

The Pachycephalosaurus was eventually tranquilised by Mac Rendell, and shortly after the unconscious creature sneezed the natural hallucinogen from its diet onto Evan Cross. Ken Leeds subsequently took the Pachycephalosaurus away and secretly had it sent to Project Magnet's research laboratory.

The Inquisition


The dead Pachycephalosaurus at Project Magnet's lab. (The Inquisition)

At Project Magnet's research lab, the Pachycephalosaurus was subjected to several experiments, including what appeared to be brain surgery or brain vivisection, until at some point it apparently died from the experiments.

Real life

Pachycephalosaurus (name meaning "thick headed lizard") was a genus of pachycephalosaurid dinosaur, which lived from 70 to 66 million years ago in what is now North America, and was one of the last non-avian dinosaurs before the K-T mass extinction event. It was omnivorous and is the largest known pachycephalosaur. Though it was initially hypothesised that Pachycephalosaurus' domed skull was used for combat with its own kind, this has been disputed in recent years. Pachycephalosaurus remains have been found in Montana, Wyoming and South Dakota.