Pachycephalosaurus, these large "dome heads" can be very aggressive at times especially towards predators. This high aggression has gotten to the point where they are now classified as too dangerous to get close to. The round skulls of these animals are used for defense as well as display, and are especially useful during the mating season as males will scratch and ram their heads against each other. Even when not during the mating season males will do this behavior, probably to show dominance. They've even been seen rubbing their heads on the ground and on trees, probably for marking territory or scaring away rival pachycephalosaurus. All this makes the pachycephalosaurus an interesting dinosaur indeed.