Ornithischians are a clade of mainly herbivorous dinosaurs characterized by their pelvic structure, with the pubis bone pointing backwards, simillarly to maniraptoran saurischians and unlike non-maniraptoran saurischians, whose pubis bone points forward. The name Ornithischia comes from Greek (ornitho+ischion), meaning "bird-hipped", emphasizing their pelvis's similarity with birds. Ornithischians are known for having some anatomical features often absent on other dinosaurs, such as the horns and frills found in ceratopsians (such as Triceratops), armoured backs, such as in ankylosaurs, armoured and spiky head-domes, such as in pachycephalosaurs, and various other features, found in other ornithischians, such as the well known ornithopods. Some ornithischians lived in herds, often composed by various ontogenic stages, or often composed only by one life stage, with adults forming their own groups, while youngsters form their own creches. Some ornithischians possessed filamentous pelts, often regarded as primitive feathers.
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