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Science & Nature • Paleontology

Pachycephalosaurus

Pachycephalosaurus is a genus of dome-headed, bipedal ornithischian dinosaur from the Late Cretaceous of North America.

By Ethan Anderson| Reviewed by Olivia Bennett, Standards & Fact-Checking Lead| Updated July 26, 2026|2 min read| Fact-checked

Pachycephalosaurus is a genus of dome-headed, bipedal ornithischian dinosaur from the Late Cretaceous of North America. It is best known for its thick, bony skull roof and is usually described as an herbivore or plant-eater. Fossils have been found in the western United States and Alberta, Canada.

Description

Pachycephalosaurus is famous for its extremely thick skull roof, which formed a rounded dome and may have been used in display or combat. It was a bipedal dinosaur with strong hind limbs and relatively small forelimbs.

Diet and lifestyle

Most modern references describe Pachycephalosaurus as an herbivore or plant-eater. It likely fed on low-lying vegetation, though some sources suggest it may also have eaten fruit, seeds, or insects.

Fossil record

Fossils of Pachycephalosaurus have been found in the Hell Creek and Lance formations and in other Late Cretaceous deposits of western North America. Reported finds include sites in Montana, South Dakota, Wyoming, Colorado, and Alberta.

Classification

Pachycephalosaurus belongs to Pachycephalosauria, a group of bird-hipped dinosaurs known for thickened skulls. It is one of the largest and best-known members of that group.

Key facts

  • Pachycephalosaurus was a bipedal dinosaur with a thick, domed skull.
  • It lived in western North America during the Late Cretaceous.
  • The genus name means “thick-headed lizard.”
  • It is commonly described as a herbivore that likely fed on low-growing plants.
  • Fossils have been reported from the United States and Canada.
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Canadian context

Pachycephalosaurus fossils have been found in Alberta, making it relevant to Canadian paleontology and the fossil record of western Canada.

Frequently asked questions

What does Pachycephalosaurus mean?
It means “thick-headed lizard,” a reference to its domed skull.
When did Pachycephalosaurus live?
It lived in the Late Cretaceous, roughly 76 to 66 million years ago.
Where did Pachycephalosaurus live?
It lived in North America, especially the western region that is now the United States and Canada.
What did Pachycephalosaurus eat?
It is generally described as a herbivore that likely ate low-growing plants; some sources suggest fruit, seeds, or insects may also have been part of its diet.
How big was Pachycephalosaurus?
It was one of the largest pachycephalosaurs, reaching about 4.5 to 5 metres in length.
Why is Pachycephalosaurus famous?
It is best known for its unusually thick, dome-shaped skull, one of the most distinctive head structures among dinosaurs.

References

  1. National Geographic Kids — https://kids.nationalgeographic.com/animals/prehistoric/facts/pachycephalosaurus
    Supports: Thick skull, meaning of name, Late Cretaceous North American range, extinction context
  2. Natural History Museum — https://www.nhm.ac.uk/discover/dino-directory/pachycephalosaurus.html
    Supports: Late Cretaceous age, bipedal stance, beak, domed skull with spikes and bumps
  3. Britannica Kids — https://kids.britannica.com/kids/article/Pachycephalosaurus/390077
    Supports: Meaning of name, skull dome, approximate size, North American fossils including Alberta, Canada, probable plant-based diet
  4. Encyclopaedia Britannica — https://www.britannica.com/animal/Pachycephalosaurus
    Supports: Genus classification, Late Cretaceous deposits in North America, approximate length, bipedal build
  5. National Geographic — https://www.nationalgeographic.com/animals/facts/pachycephalosaurus-wyomingensis
    Supports: Largest pachycephalosaurids, skull thickness, probable low-lying plant diet