Wyoming, and Alberta. Mainly known from a single skull and a few extremely thick skull roofs (at 22 cm thick), Pachycephalosaurus is estimated to have reached 4.5 m long and weighed 370 - 450 kg. More complete fossils would come to be found in the following years.

Like other pachycephalosaurids, Pachycephalosaurus was a bipedal herbivore, possessing long, strong legs and