Ceratopsids, horned herbivorous ornithischians from the Cretaceous of North America, are unique among dinosaurs in the form and expression of their cranial ornamentation. All ceratopsid genera possess a bony parieto-squamosal frill that projects over the neck region and some degree of development of nasal and orbital horns. These horns vary in form and location, from low bosses (e.g., PachyrhinosaurusSternberg, 1950) to long, conical horns (e.g., TriceratopsMarsh, 1889 postorbital horns). Internal structural changes occurred along with these extreme external modifications of the skull (Forster, 1996).

A frontal sinus complex occupies space variably involving the postorbital, frontal,...

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