The Marginocephalia ("fringed heads") are a clade of extinct herbivorous dinosaurs that inherited a slight shelf or frill at the back of their skull from their common ancestor back in the Early/mid Cretaceous period. This "margin" was elaborated differently in the two main subgroups of the Marginocephalia. You are probably familiar with some of these taxa they include the "bone-headed" pachycephalosaurs (below left) and the frilled Ceratopsians, such as the early Protoceratops and the famous Triceratops (below right).
Marginocephalia is one of three major groups of the Ornithischia, or "bird-hipped" dinosaurs. They are closely related to the Ornithopoda and some scientists suggest that the origin of Marginocephalia may lie within that group.
Skull of Pachycephalosaurus at the Denver Museum of Nature & Science.
Visitors examine a Triceratops skull in the Valley Life Sciences Building, UC Berkeley campus.
Original page created by Brian Speer and John Hutchinson 12/1997; modifications since 2005 by David Smith. Pachycephalosaurus skull photo © 1996 Pamela J.W. Gore, Georgia Perimeter College. Triceratops skull photo by Dave Smith, © UCMP.