Ornithischia (/ɔːrnɪˈθɪskiə/) is an extinct clade of mainly herbivorous dinosaurscharacterized by a pelvic structure superficially similar to that of birds.[2] The name Ornithischia, or "bird-hipped", reflects this similarity and is derived from the Greek stem 'ornith-' (ὀρνιθ-), meaning "of a bird", and 'ischion' (ἴσχιον), plural 'ischia', meaning "hip joint". However, birds are only distantly related to this group as birds are theropod dinosaurs.[2]

Ornithischians with well known anatomical adaptations include the ceratopsians or "horn-faced" dinosaurs (e.g. Triceratops), armored dinosaurs (Thyreophora) such as stegosaurus and ankylosaurspachycephalosaurids and the ornithopods.[2] There is strong evidence that certain groups of ornithischians lived in herds,[2][3] often segregated by age group, with juveniles forming their own flocks separate from adults.[4] Some were at least partially covered in filamentous (hair- or feather- like) pelts, and there is much debate over whether these filaments found in specimens of Tianyulong,[5] Psittacosaurus,[6] and Kulindadromeusmay have been primitive feathers.[7]

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After: Stegosaurus


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