The Marginocephalia or "fringed heads" were a specialised group of Ornithischians defined by a small shelf or frill at the back of their skull. There are two main types, the dome heads and the horned dinosaurs, which evolved from a common ancestor during the early Cretaceous. With the exception of one or two questionable Gondwana forms, the group appears to be limited to Laurasia.
Narrow parietal shelf; post squamosal shelf; short post maxillary plate; vomers contact maxilla (maxillae meet on midline) rather than premaxilla; premaxillae excluded from internal nares; no obturator process on ischium; pubis short, with loss of pubic symphysis.
Links: DinoData: Marginocephalia; Introduction to the Marginocephalia; Marginocephalia - EnchantedLearning.com; New Page 6; The Natural History Museum's Dino Directory; Pachycephalosaurs and Ceratopsians (November 5). ATW011227.