A skull 25 centimetres thick
The dome on top of its head was solid bone, up to 25 centimetres thick.
The plant-eaters · Horned and dome-headed dinosaurs
Pachycephalosaurus
Thick-headed lizard · PAK-ee-SEF-ah-lo-SORE-us
A two-legged plant-eater with a domed skull ringed by bony knobs and short spikes.
- Size
- About 4.5m long; 450kg
- Lived
- About 70 to 66 million years ago
- Found in
- Western North America
Trots after you, head down. Move your pointer and see.
To scale
How big was it?
The bars are drawn to the same scale. On these pages the animals are sized in proportion to each other as far as a screen allows: the giants are shrunk a little and the smallest are enlarged, so that you can see them all.
Good to know
Six things about the pachycephalosaurus
Did it butt heads?
Many domes show healed injuries, which suggests they were used for butting, perhaps at a rival's flanks.
The young looked different
Young ones had flat heads with long spikes. They were once thought to be separate kinds of dinosaur.
Leaf-shaped teeth
It had small, leaf-shaped teeth, and may have eaten insects and fruit as well as leaves.
Known mostly from domes
The thick domes survive well. The rest of the skeleton is hardly known.
Another late arrival
It lived alongside Triceratops and Tyrannosaurus, right at the end.
The real thing
Photos of the pachycephalosaurus
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Photos are from Wikimedia Commons, used under the free licences shown. They have been resized, and cropped where they appear in link previews.
What it ate
Leaves, seeds, fruit and perhaps insects.
How we know
Scans of the domes show the pattern of healed wounds.
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