Neornithischia ("new ornithischians") is a

clade A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. Rather than the English term, ...

of the dinosaur order

Ornithischia Ornithischia () is an extinct order 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 s ...

. It is 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 Ceratopsia or Ceratopia ( or ; Greek: "horned faces") is a group of herbivorous, beaked dinosaurs that thrived in what are now North America, Europe, and Asia, during the Cretaceous Period, although ancestral forms lived earlier, in the Jurassic. ...

, while the latter typically includes '' Hypsilophodon'' and the more derived Iguanodontia.

Classification

Neornithischia was first named by Cooper in 1985 and defined as "all genasaurians more closely related to ''

Parasaurolophus walkeri ''Parasaurolophus'' (; meaning "near crested lizard" in reference to ''Saurolophus)'' is a genus of herbivorous hadrosaurid ornithopod dinosaur that lived in what is now North America and possibly Asia during the Late Cretaceous Period, about ...

'' than to '' Ankylosaurus magniventris'' or '' Stegosaurus stenops''". In 2021, Neornithischia was given a formal definition under the PhyloCode: "The largest clade containing '' Iguanodon bernissartensis'' and ''

Triceratops horridus ''Triceratops'' ( ; ) is a genus of herbivorous chasmosaurine ceratopsid dinosaur that first appeared during the late Maastrichtian stage of the Late Cretaceous period, about 68 million years ago in what is now North America. It is one ...

'' but not '' Ankylosaurus magniventris'' and '' Stegosaurus stenops''."Madzia D, Arbour VM, Boyd CA, Farke AA, Cruzado-Caballero P, Evans DC. 2021. The phylogenetic nomenclature of ornithischian dinosaurs. ''PeerJ'' 9:e1236

/ref> A 2017 study by Matthew G. Baron,

David B. Norman David Bruce Norman (born 20 June 1952 in the United Kingdom) is a British paleontologist, currently the main curator of vertebrate paleontology at the Sedgwick Museum, Cambridge University. From 1991 to 2011, Norman has also been the Sedgwick Mus ...

, 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: The cladogram below results from analysis by Herne ''et al.'', 2019. '' Parksosaurus'' and Elasmaria were recovered within Ornithopoda, among other revised relationships.

References

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External links

Encyclopædia Britannica

Bajocian first appearances Maastrichtian extinctions {{ornithischian-stub