Ornithischia

Ornithischians Temporal range: Late Triassic–Late Cretaceous, 231.4–66 Ma PreЄ Є O S D C P T J K Pg N
Diversity of ornithischian dinosaurs.
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Reptilia
Clade:	Dinosauria
Order:	†Ornithischia Seeley, 1888
Subgroups
†Eocursor †Fabrosaurus †Pisanosaurus †Taveirosaurus †Trimucrodon †Heterodontosauridae †Genasauria †Neornithischia †Thyreophora
Synonyms
PredentataMarsh, 1894

Ornithischia (/ɔːrnᵻˈθɪskiə/ or-ni-thiss-kee-ə) is an extinct clade of mainly herbivorous dinosaurs characterized by a pelvic structure similar to that of birds. The name Ornithischia, or "bird-hipped", reflects this similarity and is derived from the Greek ornitheos (ορνιθειος) meaning "of a bird" and ischion (ισχιον) meaning "hip joint". Birds are members of the saurischian, or "lizard-hipped", dinosaurs.

Ornithischia is well-supported as one of the two major groups in the Dinosauria. Many characteristics define the group though most are thought to be linked to herbivory.

Ornithischians with well known anatomical adaptations include the ceratopsians or "horn-faced" dinosaurs (e.g. Triceratops), armored dinosaurs (Thyreophora) such as stegosaurs and ankylosaurs, pachycephalosaurids and the ornithopods. There is strong evidence that certain groups of ornithischians lived in herds, often segregated by age group, with juveniles forming their own flocks separate from adults.

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,Psittacosaurus, and Kulindadromeus may have been primitive feathers.