Pachycephalosaurus’s name means, very directly, “thick-headed lizard.” It was about 15 feet long and lived in what’s now North America at the end of the Cretaceous, alongside T. rex and Triceratops. The most striking thing about it was its huge domed head - 8 inches of solid bone on top of the skull, surrounded by short bony knobs around the dome.
For a long time, scientists thought Pachycephalosaurus used its head to ram other Pachycephalosaurus, the way modern bighorn sheep slam horns to settle who’s boss. We’ve found some skulls with bumps and bruises that look consistent with that.
A few scientists think the dome was more for display - too risky to ram with - but the design really does look built for impact. Either way, that thick skull would have made it nearly impossible for a small predator to bite.
