Pachycephalosaurus

dinosaur · thick skull · cretaceous

Mega-thick skull. Pachycephalosaurus had one of the thickest skulls of any dinosaur, with a dome of bone on top that was extremely hard and dense. Scientists think it used this incredible helmet to head-butt other dinosaurs.

Western giant. This dinosaur roamed what is now Montana, South Dakota, Wyoming, and Alberta during the very end of the dinosaur age, about 66 million years ago.

Big but not huge. Pachycephalosaurus grew to about 15 feet long and weighed as much as a small car, 820 to 990 pounds. Even though it looks monstrous, it was actually smaller than the truly giant dinosaurs like Triceratops.

Mystery fossil. We only know about Pachycephalosaurus from a single skull and a few thick skull roofs that scientists found. More complete skeletons might help us understand this strange dinosaur better someday.