Pachycephalosaurus

Pachycephalosaurus is famous for its incredibly thick skull. The dome on top of its head was made of solid bone, up to 10 inches thick. Its name means "thick-headed lizard." It lived about 70 million years ago.

The Bone Dome

The dome on Pachycephalosaurus's head was 10 inches of solid bone. That is as thick as a bowling ball! Some scientists think it used this dome to head-butt rivals, like bighorn sheep do today. Others think the dome was mostly for show. Small bumps and spikes surrounded the dome.

What We Know

Pachycephalosaurus was about 15 feet long and stood on two legs. It was one of the last dinosaurs alive before the extinction. We have only found its skull, never a complete skeleton. Scientists think it ate plants and maybe some small animals and insects too.

Fun Facts

• Its skull bone was 10 inches thick — about 20 times thicker than a human skull.
• No complete skeleton has ever been found, only skulls and skull fragments.
• Young Pachycephalosaurus had flat heads that became domed as they grew up.

Did You Know?

Some scientists now think Pachycephalosaurus did not actually head-butt at all. They may have bumped their domes against each other's sides instead, like giraffes do with their necks!