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This article is about the Pachycephalosaur family group, not the Pachycepalosaurus species.
Pachycephalosaurs, or "thick-headed" dinosaurs, were a group of herbivorous dinosaurs that lived during the late Cretaceous. Pachycephalosaurs lived in North America and Asia, and typically had a domed skull roof several inches thick, although other species, have more flattened skull.
While two types of pachycephalosaurs have been encountered: Dracorex and Pachycephalosaurus, some studies suggest that Dracorex (and other pachycephalosaurs) may be specimens of Pachycephalosaurus because the dome and horns were not well-developed, either because the animal was a juvenile or a female.