The Pachycephalosaur "thick-headed lizard" lived in the Cretaceous, about 70 million years ago. Little is known about this herbivorous biped. It measured 13 to 16 feet long and weighed nearly 2 tons. His specificity is undoubtedly the big dome-shaped hump on his skull. It is made of very thick and extremely strong bone, and is a kind of "helmet" whose role is not proven. It is supposed that the males clashed by great impulses. These dinosaurs had small curved teeth in the front of the mouth and also had a beak.