Stygimoloch

Stygimoloch was a thick-skulled plant-eating dinosaur (a pachycephalosaur) that walked on two legs. This unusual-looking dinosaur had bony spikes and bumps on its skull; the many horns ranged up to 4 inches (100 mm) long. Pachycephalosaurs probably engaged in head-butting both as a defense and as intra-species rivalry.