Neornithischia ("new ornithischians") is a clade of the dinosaur order Ornithischia. They are the sister group of the Thyreophora within the clade Genasauria. Neornithischians are united by having a thicker layer of asymmetrical enamel on the inside of their lower teeth. The teeth wore unevenly with chewing and developed sharp ridges that allowed neornithischians to break down tougher plant food than other dinosaurs. Neornithischians include a variety of basal forms historically known as "hypsilophodonts", including the Parksosauridae; in addition, there are derived forms classified in the groups Marginocephalia and Ornithopoda. The former includes clades Pachycephalosauria and Ceratopsia, while the latter typically includes Hypsilophodon and the more derived Iguanodontia.
|Hypsilophodon skeletal mount at the Brussels Science Institute|
Neornithischia was first named by Cooper in 1985 and defined as "all genasaurians more closely related to Parasaurolophus walkeri Parks, 1922, than to Ankylosaurus magniventris Brown, 1908 or Stegosaurus stenops Marsh, 1877a".
A 2017 study by Matthew G. Baron, David B. Norman, and Paul M. Barrett recovered the Early Jurassic taxon Lesothosaurus diagnosticus from Southern Africa as the most basal known member of Neornithischia – a position previously held by Stormbergia dangershoeki (a taxon considered by the authors to be an adult form of Lesothosaurus and therefore a junior subjective synonym). However, Baron et al. go on to state that this result is only poorly supported and that future studies will be needed in order to better resolve the base of the ornithischian tree.
The below cladogram follows an analysis by Clint A. Boyd published in 2015 on the relationships of neornithischians:
Averostra, or "bird snouts", is a clade that includes most theropod dinosaurs that have a promaxillary fenestra (fenestra promaxillaris), an extra opening in the front outer side of the maxilla, the bone that makes up the upper jaw. Two groups of averostrans, the Ceratosauria and the Orionides, survived into the Cretaceous period. When the Cretaceous–Paleogene extinction event occurred, ceratosaurians and two groups of orionideans within the clade Coelurosauria, the Tyrannosauroidea and Maniraptoriformes, were still extant. Only one subgroup of maniraptoriformes, Aves, survived the extinction event and persisted to the present day.Avetheropoda
Avetheropoda, or "bird theropods", is a clade that includes carnosaurians and coelurosaurs to the exclusion of other dinosaurs.Cerapoda
Cerapoda ("ceratopsians and ornithopods") is a clade of the dinosaur order Ornithischia.Changchunsaurus
Changchunsaurus (meaning "Changchun lizard") is an extinct genus of small herbivorous parksosaurid dinosaur from Early Cretaceous deposits of Gongzhuling, Jilin, China. It is the first named dinosaur genus from Jilin.Claorhynchus
Claorhynchus (meaning "broken beak", as it is based on broken bones from the snout region) is a dubious genus of cerapodan dinosaur with a confusing history behind it. It has been considered to be both a hadrosaurid and a ceratopsid, sometimes the same as Triceratops, with two different assignments as to discovery formation and location, and what bones make up its type remains.Elasmaria
Elasmaria is a clade of iguanodont ornithopods known from Cretaceous deposits in South America, Antarctica, and Australia.Genasauria
Genasauria is a clade of extinct beaked, primarily herbivorous dinosaurs. Paleontologist Paul Sereno first named Genasauria in 1986. The name Genasauria is derived from the Latin word gena meaning ‘cheek’ and the Greek word saúra (σαύρα) meaning ‘lizard.’ Genasauria is the most inclusive clade within the order Ornithischia. According to Sereno (1986), Genasauria represents all ornithischians except for the most primitive ornithischian, Lesothosaurus. Sereno’s formal definition is, “Ankylosaurus, Triceratops, their most recent common ancestor and all descendants.” It is hypothesized that Genasauria had diverged from Lesothosaurus by the Early Jurassic. Cranial features that characterize Genasauria include a medial offset of the maxillary dentition, a sprout-shaped mandibular symphysis, moderately sized coronoid process, and an edentulous (without teeth) anterior portion of the premaxilla. A distinguishing postcranial feature of Genasauria is a pubic peduncle of the ilium that is less robust than the ischial peduncle.
Genasauria is commonly divided into Neornithischia and Thyreophora. Neornithischia is characterized by asymmetrical distributions of enamel covering the crowns of the cheek teeth, an open acetabulum, and a laterally protruding ischial peduncle of the ilium. Neornithischia includes ornithopods, pachycephalosaurs, and ceratopsians. Thyreophora is characterized by body armor and includes stegosaurs, ankylosaurs, Scelidosaurus, and Scutellosaurus.Hexinlusaurus
Hexinlusaurus is a genus of basal ornithischian dinosaur from the Middle Jurassic of China. The holotype (ZDM T6001, Zigong Dinosaur Museum, Dashanpu, People's Republic of China), consists of an almost complete, articulated skull and some postcranial material, collected from a terrestrial sandstone within the Lower Shaximiao Formation (?Bajocian) at the famous dinosaur-bearing quarries at Dashanpu. A paratype (ZDM T6002) consists of a partial skull and postcranial remains. Previously, it had been described as a species of Yandusaurus, Y. multidens (He and Cai, 1983), but was reclassified as a new taxon by Paul M. Barrett, Richard J. Butler and Fabien Knoll in 2005, who diagnosed this anatomically conservative species as follows: "A small ornithischian dinosaur distinguished from all other basal ornithischians by a single autapomorphy, the presence of a marked concavity that extends over the lateral surface of the postorbital." The etymology of the genus name honors Professor He Xin-Lu (from the Chengdu University of Technology) who originally named the specimen as Y. multidens + the Greek sauros (=lizard). Hexinlusaurus was a small, fleet-footed herbivore.
Other dinosaurs known from Dashanpu include the sauropod Shunosaurus, the theropod Gasosaurus, and the stegosaur Huayangosaurus.
Before being officially named Hexinlusaurus, this genus was briefly known under the informal name "Proyandusaurus". This name originally appeared in an abstract attributed to Fabien Knoll, which was apparently published without his consent.Jeholosauridae
Jeholosaurids were herbivorous neornithischian dinosaurs from the Cretaceous Period (Aptian - Santonian, with a possible Campanian record) of Asia. The family was first proposed by Han et al. in 2012. The jeholosaurids were defined as those ornithischians more closely related to Jeholosaurus shangyuanensis than to Hypsilophodon foxii, Iguanodon bernissartensis, Protoceratops andrewsi, Pachycephalosaurus wyomingensis, or Thescelosaurus neglectus. The Jeholosauridae includes the type genus Jeholosaurus and Yueosaurus.Jingshanosaurus
Jingshanosaurus (meaning "Jingshan lizard") is a genus of sauropodomorph dinosaurs from the early Jurassic period.Kulindadromeus
Kulindadromeus was a herbivorous dinosaur, a basal neornithischian from the Jurassic. The first Kulindadromeus fossil was found in Russia. Its feather-like integument is evidence for protofeathers being basal to Dinosauria as a whole, rather than just to Coelurosauria, as previously suspected.Lesothosaurus
Lesothosaurus was a genus of omnivorous ornithischian dinosaur from South Africa and Lesotho. It was named by paleontologist Peter Galton in 1978, the name meaning "lizard from Lesotho". The genus has only one valid species, Lesothosaurus diagnosticus.Neotheropoda
Neotheropoda (meaning "new theropods") is a clade that includes coelophysoids and more advanced theropod dinosaurs, and the only group of theropods who survived the Triassic–Jurassic extinction event. Yet all of the neotheropods became extinct during the early Jurassic period except for Averostra.Orionides
Orionides is a clade of tetanuran theropod dinosaurs from the Middle Jurassic to the Present. The clade includes most theropod dinosaurs, including birds.Ornithischia
Ornithischia () 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 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.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.Orodrominae
Orodrominae is a subfamily of parksosaurid dinosaurs from the Cretaceous of North America and Asia.Parksosauridae
Parksosauridae is a clade or family of small ornithischians which have previously been generally allied to hypsilophodontids. Parksosauridae is often considered a synonym of Thescelosauridae, but the two groups cannot be synonyms because Parksosauridae is defined as a stem, while Thescelosauridae is defined as a node.Phyllodon
Phyllodon (meaning "leaf tooth") was a genus of small ornithischian dinosaur from the Kimmeridgian-age Upper Jurassic Guimarota Formation of Leiria, Portugal. It may have been closely related to contemporaneous dinosaurs in North America.
This genus is known from teeth and possibly partial lower jaws. The name is also in use for a genus of modern moss, but this is not considered to be a problem because the two organisms are in two different kingdoms.Yandusaurus
Yandusaurus is a genus of herbivorous basal neornithischian dinosaur from the Bathonian age (middle Jurassic, approximately 168 to 162;Ma) of China.