Dino card No. 1332 of 2,015

Pachycephalosaurus

Say it: PAK-ee-SEF-uh-loh-SORE-us

Name means: “thick-headed lizard”1

Ate: PlantsDome-headsLate Cretaceous

Pachycephalosaurus was a dinosaur with a super thick, bony dome on its head. It walked on two legs and used its beak to snip plants. It lived at the very end of the Age of Dinosaurs, about 69 to 66 million years ago.1 2

Lived

84 to 66 million years ago3

Late Cretaceous

Fossils found in

Montana, South Dakota, Wyoming, and Alberta, Canada3 1 2

Food

Plants1 2

Length

4.5 m2

Weight

370 kg to 450 kg2

Artist's life restoration of Pachycephalosaurus — How Pachycephalosaurus may have looked, by Fred Wierum. CC BY 4.0, via Wikimedia Commons. Scientists still argue about colours and details.

When did it live?

Triassic

Jurassic

Cretaceous

252 million years ago20114566, the asteroid

How big was it?

cool stuff

Fun facts

The bony dome on its skull could be up to 25 centimetres (10 inches) thick, safely cushioning its tiny brain.2

Scientists used to think Stygimoloch and Dracorex were different dinosaurs, but now most believe they were just young Pachycephalosaurus.1 2

The first Pachycephalosaurus fossil was found around 1860 and was thought to be from an armadillo-like creature. It was named Tylosteus.1 2

Pachycephalosaurus was one of the last non-bird dinosaurs alive before the big extinction 66 million years ago.2

Its dome may have been used for head-butting fights, like bighorn sheep, but some scientists now disagree.2

Pachycephalosaurus had a beak for cropping plants and small, serrated teeth that could also shred meat, so it might have eaten some meat too.2

Myth buster

Myth: Pachycephalosaurus used its dome to ram into rivals at full speed.

Truth: The dome was probably used for head-butting, but the shape and structure suggest it was more for pushing or flank-butting, not full-speed ramming.2

For dino experts

Scientific name: Pachycephalosaurus
Named by: Brown and Schlaikjer 19433
Group: Dome-heads
Family / clade: Eupachycephalosauria3
Classification: Ornithischia > Pachycephalosauria3
Age of the rocks: 84 to 66 million years (Campanian to Maastrichtian)3
Rock formations: Hell Creek, Lance, Ferris3
Countries: USA, Canada3
Fossil records: 34 in the Paleobiology Database3
Also known as: Dracorex, Stenotholus, Stygimoloch, Tylosteus (older names now counted as the same animal)3
Discovery: The name Pachycephalosaurus was created in 1943 by Barnum Brown and Erich Maren Schlaikjer after more complete skulls were found in Montana and South Dakota.1 2
Still debated: Scientists still debate whether Stygimoloch and Dracorex are really just young Pachycephalosaurus or separate species.2

Where the facts come from

Pachycephalosaurus | Natural History Museum (nhm.ac.uk)
Pachycephalosaurus (en.wikipedia.org)
Pachycephalosaurus in The Paleobiology Database (CC BY 4.0): age, places, rock formations, classification.

Every fact on this page has a number that points to its source. If we got something wrong, sorry, we are dino fans, not a science journal. Tell us at [email protected] and we will fix it.