Stegoceras validum

Stegoceras was a pachycephalosaur, or dome-headed dinosaur, from the Late Cretaceous of Alberta, about 75 million years ago. A small (2.4 m / 6.5 foot long) bipedal plant-eater, it had a thickened dome of bone crowning its skull, likely used in display or for butting (whether head-to-head, or head-to-flank contests are more likely is still a subject of debate).