Delicate Domes

Part of the Dinosaurs: Ancient Fossils, New Discoveries exhibition.

Using Their Heads?

A great way to learn about long-extinct animals is to study modern creatures that share similar features. But sometimes animals that seem the same at first glance turn out to be quite different from each other.

© Raul Martin



The group of dinosaurs known as pachycephalosaursids had distinctive heads, with high, round skulls. Scientists once thought that modern bighorn sheep, with their two large, rounded horns, could provide a model for the behavior of dome-headed dinosaurs. But more recent research has overturned this idea.

Bighorn Sheep Skull

The horns of a modern bighorn sheep create a broad, flat area on the front of the skull, which is better suited to head-to-head combat than the rounded skulls of dome-headed dinosaurs. Hollow spaces inside the sheep's skull serve to absorb the force of blows. These hollow spaces are not present in adult pachycephalosaurid skulls.


The round shape of a Pachycephalosaurus skull would have made it hard for these dinosaurs to fight in head-to-head combat. Their heads would have essentially glanced off each other, or the animals would have been injured if their heads twisted to the side upon impact.

New Idea: Delicate Domes

Male bighorn sheep compete for females in head-to-head combat, running at each other repeatedly at high speeds. Did pachycephalosaurids fight in the same way, relying on their thick skulls to protect them from injury?

Probably not. The dinosaurs' rounded skulls are poorly designed for head-butting matches. And new research by paleontologists Mark Goodwin and John Horner suggests the bone was too weak to withstand head-on blows. Instead, the skulls of dome-headed dinosaurs might have been used to help members of the same species recognize each other and compete for mates.

If male pachycephalosaurids fought with their heads in contests for females, they may have hit opponents on their sides, much as modern bison do.

Fast Facts: Pachycephalosaurus

  • Species: Pachycephalosaurus wyomingensis
  • Pronunciation: "pack-ee-SEF-uh-low-sore-us why-om-ing-EN-sis"
  • LENGTH: about 8 meters (26 feet)
  • HEIGHT: about 6 meters (20 feet)
  • WEIGHT: about 3,000 kilograms (6,600 pounds)
  • Food: plants
  • When it lived: 66 million years ago