"bordered heads." These animals all have some kind of bony frill at the back of the skull. The group includes the pachycephalosaurs and ceratopsians.

Marginocephalia ("fringed heads") is a clade of ornithischian dinosaurs that includes the thick-skulled pachycephalosaurids, and horned ceratopsians. They were all herbivores, walking on two or four legs, and are characterized by a bony ridge or frill the back of the skull. The clade evolved in the Jurassic period, and became common in the Upper Cretaceous.