Marginocephalia

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.

Phylogeny
The cladogram below follows a 2009 analysis by Zheng and colleagues.