Marginocephalia

Marginocephalia is a clade of ornithischian dinosaurs that includes ceratopsians and pachycephalosaurs, united by distinctive expansions of the skull margin.

Ornithischia: Ornithischia is one of the two major dinosaur lineages, characterized by a backward-pointing pubis and diverse herbivorous forms. Marginocephalia is nested within this major dinosaur lineage.
Phylogenetic systematics: Phylogenetic systematics classifies organisms by reconstructing shared ancestry from inherited characteristics. Marginocephalia is a clade inferred from shared derived anatomical traits.
Ceratopsian: Ceratopsian is a name coined by Othniel Charles Marsh for horned dinosaurs and their close relatives. The group’s naming and early study helped establish one half of Marginocephalia.
Triceratops: Triceratops is a large, three-horned ceratopsian dinosaur from the Late Cretaceous of North America. Its horns and broad frill exemplify the elaborate skull margins of derived ceratopsians.
Ceratopsia: Ceratopsia is the dinosaur group that includes parrot-beaked forms such as Triceratops and their relatives. This is one of the two principal branches included in Marginocephalia.
Synapomorphy: A synapomorphy is a derived trait shared by members of a group and inherited from their common ancestor. Proposed shared skull traits help diagnose Marginocephalia as a clade.
Pachycephalosaur: Pachycephalosaur is a name for thick-skulled ornithischian dinosaurs, a group recognized through distinctive skull fossils. Recognition of this group established Marginocephalia’s second major component.
Protoceratops: Protoceratops is a small, beaked ceratopsian known from Late Cretaceous fossils in Mongolia. Its modest frill illustrates ceratopsian anatomy without the large horns of later relatives.
Pachycephalosauria: Pachycephalosauria is a group of ornithischian dinosaurs known for thickened, often domed skull roofs. This is Marginocephalia’s other principal branch.
Supratemporal fenestra: A supratemporal fenestra is an opening in the skull roof behind the eye socket. Its reduction or closure features in discussions of skull evolution among marginocephalians.

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