You don’t get to headbutt your way through life without picking up a few scars along the way. If you repeatedly ram your skull against your peers, you’ll pick up injuries, especially on the parts that suffer the most impacts. And when you die, your skeleton will preserve a record of your violent past.

The most popular answer is that these dinosaurs used their skulls as battering rams, charging each other head-on to fight over mates, territories or both. The domes would have protected their brain during such collisions. But other dinosaur specialists, like Mark Goodwin and Jack Horner, have said that the dome was too brittle to be used as a ram. Instead, they think it was a