Pachycephalosaurus Facts for Kids
PACK-ee-SEF-uh-loh-SORE-us · its name means “thick-headed lizard”
A two-legged plant-eater with a thick dome of bone on its head.
- 📏 15 to 16 ft4.6 to 4.9 m1 long
- ⚖️ 816 to 992 lb370 to 450 kg1
- 🕰️ 66 to 72 million years ago66 to 72 million years ago1
- 🍽️ plants
Pachycephalosaurus had a big round dome on its head. The dome was thick bone. It walked on two legs.
The dome on top of Pachycephalosaurus's head was solid bone, much thicker than your skull. Little bumps and spikes ringed the back of its head. It walked on two legs and ate plants.
Scientists still argue about what the dome was for. Some think these dinosaurs bumped heads or shoved each other's sides when they competed, like goats or bighorn sheep do; others think the dome was mostly for show. Young ones had flatter heads, and the dome grew as they did.
Every dinosaur number is scientists’ best guess from bones, so each one says where it came from.
How big was Pachycephalosaurus?
Pachycephalosaurus in numbers
| Length (nose to tail) | 15 to 16 ft4.6 to 4.9 m1scientists' estimate |
|---|---|
| Height at the hips | 4.9 to 6.9 ft1.5 to 2.1 m1at the hips |
| Weight | 816 to 992 lb370 to 450 kg1scientists' estimate |
| When it lived | 66 to 72 million years ago66 to 72 million years ago1the Late Cretaceous |
| What it ate | plants, and maybe some fruit and seeds |
| Fossils found in | western North America, including Montana, Wyoming and the Dakotas |
| What kind | a pachycephalosaur: a dome-headed plant-eater |
Wow!
- Its dome was solid bone.
- Its name means thick-headed lizard.
- Young ones had flatter heads than grown-ups.
🦴 Pachycephalosaurus’s bones
Books about Pachycephalosaurus, free at the library
Ask a grown-up to tap the button: it shows where to borrow a book about Pachycephalosaurus for free.
Where was the land back then?
The continents were in different places when Pachycephalosaurus lived, 66 to 72 million years ago. Open Planet Earth, pick Drifting continents, and slide back in time to see where the land was.
Its neighbours in time
Where these numbers come from
- USDA Forest Service, Dakota Prairie Grasslands: prehistoric animals, checked 30 October 2026.
- Wikidata, Pachycephalosaurus (Q14455), checked 30 October 2026.
To read more: the Natural History Museum’s Dino Directory (see also, not copied).