Neornithischia ("new ornithischians") is a

clade In biology, a clade (), also known as a Monophyly, monophyletic group or natural group, is a group of organisms that is composed of a common ancestor and all of its descendants. Clades are the fundamental unit of cladistics, a modern approach t ...

of the

dinosaur Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic Geological period, period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the #Evolutio ...

order

Ornithischia Ornithischia () 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 ...

. It is the sister group of the

Thyreophora Thyreophora ("shield bearers", often known simply as "armored dinosaurs") is a group of armored ornithischian dinosaurs that lived from the Early Jurassic until the end of the Cretaceous. Thyreophorans are characterized by the presence of bod ...

within the clade

Genasauria Ornithischia () 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 st ...

. 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 "

hypsilophodont Hypsilophodontidae (or Hypsilophodontia) is a traditionally used family of ornithopod dinosaurs, generally considered invalid today. It historically included many small bodied bipedal neornithischian taxa from around the world, and spanning from ...

s", including the

Thescelosauridae Thescelosauridae is a clade of neornithischians from the Cretaceous of East Asia and North America. The group was originally used as a name by Charles M. Sternberg in 1937, but was not formally defined until 2013, where it was used by Brown and ...

. As these taxa do not all form a

monophyletic In biological cladistics for the classification of organisms, monophyly is the condition of a taxonomic grouping being a clade – that is, a grouping of organisms which meets these criteria: # the grouping contains its own most recent co ...

clade, the term 'small-bodied early diverging ornithischian' (SBEDO) has been used to refer to these as a collective group. In addition, there are derived forms classified in the groups Marginocephalia and

Ornithopoda Ornithopoda () is a clade of ornithischian dinosaurs, called ornithopods (). They represent one of the most successful groups of herbivorous dinosaurs during the Cretaceous. The most primitive members of the group were bipedal and relatively sm ...

. The former includes clades

Pachycephalosauria Pachycephalosauria (; from Greek παχυκεφαλόσαυρος for 'thick headed lizards') is a clade of ornithischian dinosaurs. Along with Ceratopsia, it makes up the clade Marginocephalia. With the exception of two species, most pachyceph ...

and

Ceratopsia Ceratopsia or Ceratopia ( or ; Ancient Greek, Greek: "horned faces") is a group of herbivore, herbivorous, beaked dinosaurs that thrived in what are now North America, Asia and Europe, during the Cretaceous Period (geology), Period, although ance ...

, while the latter typically includes ''

Hypsilophodon ''Hypsilophodon'' (; meaning "high-crested tooth") is a neornithischian dinosaur genus from the Early Cretaceous period of England. It has traditionally been considered an early member of the group Ornithopoda, but recent research has put this ...

'' and the more derived

Iguanodontia Ornithopoda () is a clade of ornithischian dinosaurs, called ornithopods (). They represent one of the most successful groups of herbivorous dinosaurs during the Cretaceous. The most primitive members of the group were bipedal and relatively sm ...

Classification

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

Ankylosaurus magniventris ''Ankylosaurus'' is a genus of armored dinosaur. Its fossils have been found in geological formations dating to the very end of the Cretaceous Period, about 68–66 million years ago, in western North America, making it among the last of th ...

'' or ''

Stegosaurus stenops ''Stegosaurus'' (; ) is a genus of herbivorous, four-legged, armored dinosaur from the Late Jurassic, characterized by the distinctive kite-shaped upright plates along their backs and spikes on their tails. Fossils of the genus have been foun ...

''". In 2021, Neornithischia was given a formal definition under the

PhyloCode The ''International Code of Phylogenetic Nomenclature'', known as the ''PhyloCode'' for short, is a formal set of rules governing phylogenetic nomenclature. Its current version is specifically designed to regulate the naming of clades, leaving the ...

: "The largest clade containing ''

Iguanodon bernissartensis ''Iguanodon'' ( ; meaning 'iguana-tooth'), named in 1825, is a genus of iguanodontian dinosaur. While many species found worldwide have been classified in the genus ''Iguanodon'', dating from the Late Jurassic to Early Cretaceous, Taxonomy (bi ...

'' and ''

Triceratops horridus ''Triceratops'' ( ; ) is a genus of Chasmosaurinae, chasmosaurine Ceratopsia, ceratopsian dinosaur that lived during the late Maastrichtian age of the Late Cretaceous Period (geology), period, about 68 to 66 million years ago on the island ...

'' but not ''

'' and ''

''."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, 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. Pyrodontia was named by André O. Fonseca and colleagues in 2024 to unite the members of

and Cerapoda. Its name translates to "fire teeth" in reference to the rapid diversification of this clade during the Middle Jurassic. The clade is formally defined in the ''

'' as "the smallest clade containing '' Ceratops montanus'', ''

'', ''

Pachycephalosaurus wyomingensis ''Pachycephalosaurus'' (; meaning "thick-headed lizard", from Ancient Greek, Greek ''pachys-/'' "thickness", ''kephalon/'' "head" and ''sauros/'' "lizard") is a genus of pachycephalosaurid Ornithischia, ornithischian dinosaur. The type species, ...

'', and ''

Thescelosaurus neglectus ''Thescelosaurus'' ( ) is a genus of ornithischian dinosaur that lived during the Late Cretaceous period in western North America. It was named and described in 1913 by the paleontologist Charles W. Gilmore; the type species is ''T. neglectus''. ...

''. Cerapoda is the most diverse clade within Neornithischia. The name "Cerapoda" is a portmanteaux of "Ceratopsia" and "Ornithopoda". As the name suggests, the clade is divided into two groups:

("bird-foot") and Marginocephalia ("fringed heads"). The latter group includes the

("thick-headed lizards") and

("horned faces"). The following taxonomy follows

Richard J. Butler Richard James Butler is a vertebrate palaeontologist at the University of Birmingham, where he holds the title of professor of palaeobiology. His research focuses on ornithischian dinosaur evolution, dinosaur origins, and fossil tetrapod macroe ...

, Paul Upchurch and David B. Norman, 2008 (and Butler ''et al.'', 2011) unless otherwise noted. Cerapoda was first named by Sereno in 1986 and defined by him as "'' Parasaurolophus walkeri'' Parks, 1922, ''

'' Marsh, 1889, their most recent common ancestor and all descendants". A similar clade Neornithopoda was tentatively proposed by David B. Norman to unite ceratopsians with advanced ornithopods in a 1984 paper. In 2021, Cerapoda was given a formal definition under the

: "The smallest clade containing ''

'' Boulenger in Beneden, 1881, ''

'' (Gilmore, 1931), and ''

'' Marsh, 1889." The phylogenetic study of Fonseca and colleagues in 2024 recovered results similar to the previous analyses of Boyd and Herne and colleagues, with thescelosaurids outside Ornithopoda and heterodontosaurids outside Neornithischia, while other aspects of relationships, like the placement of ''

Changmiania ''Changmiania'' (from the Chinese "changmian", meaning "eternal sleep") is a genus of basal ornithopod dinosaur that lived in what is now China during the Early Cretaceous. It contains a single species, ''Changmiania liaoningensis''. Discovery a ...

'' or the grouping within Ornithopoda were novel results. Their equal-weights results are below.

References

* *

External links

Encyclopædia Britannica

{{Taxonbar, from=Q379167 Dinosaur clades