Pachycephalosaurus
Pachycephalosaurus wyomingensis • "Thick-Headed Lizard"
Pachycephalosaurus was a small, two-legged dinosaur from Late Cretaceous North America. It had a thick bony dome on its skull; whether the dome was used in head-butting, display, or both remains debated.
- Length
- ≈4.5 m
- Weight
- ≈0.5 t
- Diet
- Herbivore
- Danger
- ★★★★★
Overview
The heavyweight boxer of the prehistoric plains. Pachycephalosaurus wielded a solid 10-inch-thick bone dome capable of smashing into rivals during mating season and bludgeoning predators in defense.
“Studies by Jack Horner demonstrate that Dracorex and Stygimoloch are actually juvenile and sub-adult growth stages of Pachycephalosaurus, showing how the dome thickened with age.”
Key facts
Strengths
- Lethal battering-ram head strikes that break ribs and bone
- High agility and bipedal speed (sprints at 35 km/h)
- Shock-absorbing neck vertebrae and rigid torso
Weaknesses
- Light body mass compared to apex theropods (450 kg vs 8000 kg)
- Limited offensive reach beyond direct head contact
Natural weapons
- Solid 25-centimeter (10-inch) thick bone skull dome
- Bony spikes and knobs ringing the snout and back of skull
- Reinforced rigid spinal column to absorb head-on collisions
Movies vs. science
Myth: Shown ramming solid iron cages and car doors without injury.
Reality: The dome was dense and vascular, used for flank-butting and head-to-head dominance clashes with shock absorption.
Size & simulator stats
Estimated at about 3 m long and 450 kg; these measurements are reconstructions from fossils.
- Length
- 4.5 m
- Height
- 1.5 m
- Weight
- 0.5 t
Illustrative simulator values (not measured biology)
See how Pachycephalosaurus measures up in the sourced size comparison chart.
Habitat
Floodplain forests, open grasslands, and riverbanks of Cretaceous North America.
North America; fossils are known from the United States and Canada.
Diet
Herbivore/omnivore consuming seeds, roots, fruits, leaves, and occasional insects.
Likely herbivorous, although some features of its teeth have led researchers to discuss whether it may have eaten other foods.
Fossils & discovery
First described from United States in 1940 (Hell Creek Formation (Montana, South Dakota, Wyoming)).Studies by Jack Horner demonstrate that Dracorex and Stygimoloch are actually juvenile and sub-adult growth stages of Pachycephalosaurus, showing how the dome thickened with age.
Research sources
Sources checked on by the Dinosaurs Names Editorial Team. Editorial policy
Gallery
Related dinosaurs
Battle Arena
Can anything beat Pachycephalosaurus?
Send Pachycephalosaurus into an illustrative matchup against any other species and compare attack, defense, and bite force.
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