Which Dinosaur Could Have Been Called Old Thickhead?

The prize for the thickest skull goes to Pachycephalosaurus, or dome head, whose skull was four inches (25 cm) thick at the crown. Dome heads probably fought by butting heads. The swelling was protection for their small brains. Pachycephalosaurus were herbivores, which fed on lowland grasses. They appeared in the early Cretaceous Period. Their thick skulls gave them an erudite appearance in addition to the name of dome heads, but these skulls protected an unexceptional brain. Nevertheless that massive bone grew on these creatures for some reason. It may be that dome heads used their heads as a weapon of defense and attack. It is likely they engaged in head-butting contests to determine the leader of the herd or the consort of a harem of females, similar to the methods of the bighorn sheep of today.