Ornithischia

Ornithischia; Temporal range: ; Early Jurassic–Late Cretaceous, (Possible Triassic record)
	A collection of ornithischian skeletons (clockwise from top left): Triceratops (Ceratopsia), Heterodontosaurus (Heterodontosauridae), Kentrosaurus (Stegosauria), Stegoceras (Pachycephalosauria), Europelta (Ankylosauria), and Hypacrosaurus (Ornithopoda).
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Clade:	Dinosauria
Clade:	†Ornithischia; Seeley, 1888
Subgroups
	†Asilisaurus?; †Gondwanax?; †Laosaurus; †Lewisuchus?; †Soumyasaurus?; †Syngonosaurus; †Trimucrodon; †Parapredentata Norman et al., 2022 †Alocodon; †Amanasaurus?; †Diodorus?; †Eucoelophysis?; †Gamatavus?; †Gongbusaurus?; †Ignotosaurus?; †Kwanasaurus?; †Lutungutali?; †Pisanosaurus; †Sacisaurus?; †Silesaurus?; †Technosaurus?; †Saphornithischia Madzia et al., 2021 †Archaeocursor; †Eocursor; †Fabrosaurus; †Ferganocephale; †Laquintasaura; †Lesothosaurus; †Heterodontosauridae; †Genasauria Sereno, 1986 †Serendipaceratops; †Notoceratops; †Tichosteus; †Thyreophora; †Neornithischia; ; ; ;
Synonyms
	Predentata Marsh, 1894; Prionodontia Owen, 1874;

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

Ornithischians with well known anatomical adaptations include the ceratopsians or "horn-faced" dinosaurs (e.g. Triceratops), the pachycephalosaurs or "thick-headed" dinosaurs, the armored dinosaurs (Thyreophora) such as stegosaurs and ankylosaurs, 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.

Ornithischia Temporal range: Early Jurassic–Late Cretaceous, (Possible Triassic record)

A collection of ornithischian skeletons (clockwise from top left): Triceratops (Ceratopsia), Heterodontosaurus (Heterodontosauridae), Kentrosaurus (Stegosauria), Stegoceras (Pachycephalosauria), Europelta (Ankylosauria), and Hypacrosaurus (Ornithopoda).
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Clade:	Dinosauria
Clade:	†Ornithischia Seeley, 1888
Subgroups
†Asilisaurus? †Gondwanax? †Laosaurus †Lewisuchus? †Soumyasaurus? †Syngonosaurus †Trimucrodon †Parapredentata Norman et al., 2022 †Alocodon †Amanasaurus? †Diodorus? †Eucoelophysis? †Gamatavus? †Gongbusaurus? †Ignotosaurus? †Kwanasaurus? †Lutungutali? †Pisanosaurus †Sacisaurus? †Silesaurus? †Technosaurus? †Saphornithischia Madzia et al., 2021 †Archaeocursor †Eocursor †Fabrosaurus †Ferganocephale †Laquintasaura †Lesothosaurus †Heterodontosauridae †Genasauria Sereno, 1986 †Serendipaceratops †Notoceratops †Tichosteus †Thyreophora †Neornithischia
Synonyms
Predentata Marsh, 1894 Prionodontia Owen, 1874