Pachycephalosauria (Greek for "thick headed lizards") is a group of ornithischian dinosaurs which evolved during the Cretaceous period in what is now North America and Asia.
Pachycephalosauria (Greek for "thick headed lizards") is a clade (traditionally a Suborder) of ornithischian dinosaurs. Most known pachycephalosaurs lived during the Late Cretaceous in what is now North America and Asia.