Hypothetical head-to-head interactions among pachycephalosaurids. (A) Bison-like head-shoving in large, broad-domed specimens such as Pachycephalosaurus wyomingensis; (B) Ovis-like clashing in Prenocephale prenes; (C) Capra-style broadside butting in high-domed and large-horned specimens such as subadult Pachycephalosaurus (“Stygimoloch” and “Dracorex”).