Pachycephalosaurus (the 'thick headed lizard', from the Greek pachy-/παχυ- meaning 'thick', cephale/κεφαλη meaning 'head' and saurus/σαυρος meaning 'lizard') was a dinosaur of the family Pachycephalosauridae, from the Late Cretaceous Period of what is now North America. It was an herbivorous creature, which is only known from a single skull and a few extremely thick skull roofs.