| Neornithischians | |
|---|---|
 | |
| Six neornithischians (top left to bottom right):Psittacosaurus,Styracosaurus,Thescelosaurus,Kulindadromeus,Hypacrosaurus,Pachycephalosaurus | |
Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Clade: | Dinosauria |
| Clade: | †Ornithischia |
| Clade: | †Genasauria |
| Clade: | †Neornithischia Cooper, 1985 |
| Subgroups[1] | |
Neornithischia ("new ornithischians") is aclade of thedinosaur orderOrnithischia. It is the sister group of theThyreophora within the cladeGenasauria. 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 theThescelosauridae. As these taxa do not all form amonophyletic clade, the term 'small-bodied early diverging ornithischian' (SBEDO) has been used to refer to these as a collective group.[2] In addition, there are derived forms classified in the groupsMarginocephalia andOrnithopoda. The former includes cladesPachycephalosauria andCeratopsia, while the latter typically includesHypsilophodon and the more derivedIguanodontia.
Neornithischia was first named by Cooper in 1985 and defined as "all genasaurians more closely related toParasaurolophus walkeri than toAnkylosaurus magniventris orStegosaurus stenops".[3] In 2021, Neornithischia was given a formal definition under thePhyloCode: "The largest clade containingIguanodon bernissartensis andTriceratops horridus but notAnkylosaurus magniventris andStegosaurus stenops."[4]
A 2017 study by Matthew G. Baron,David B. Norman, and Paul M. Barrett recovered the Early Jurassic taxonLesothosaurus diagnosticus from Southern Africa as the most basal known member of Neornithischia – a position previously held byStormbergia dangershoeki (a taxon considered by the authors to be an adult form ofLesothosaurus and therefore a junior subjective synonym). However, Baronet 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.[5]
Pyrodontia was named by André O. Fonseca and colleagues in 2024 to unite the members ofThescelosauridae andCerapoda. Its name translates to "fire teeth" in reference to the rapid diversification of this clade during the Middle Jurassic.[1] The clade is formally defined in thePhyloCode as "the smallest clade containingCeratops montanus,Iguanodon bernissartensis,Pachycephalosaurus wyomingensis, andThescelosaurus neglectus.[1]
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:Ornithopoda ("bird-foot") andMarginocephalia ("fringed heads"). The latter group includes thePachycephalosauria ("thick-headed lizards") andCeratopsia ("horned faces"). The following taxonomy followsRichard J. Butler, Paul Upchurch andDavid B. Norman, 2008 (and Butleret al., 2011) unless otherwise noted.[3][6]
Cerapoda was first named bySereno in 1986 and defined by him as "Parasaurolophus walkeri Parks, 1922,Triceratops horridus Marsh, 1889, their most recent common ancestor and all descendants".[3] A similar clade Neornithopoda was tentatively proposed byDavid B. Norman to unite ceratopsians with advanced ornithopods in a 1984 paper.[7] In 2021, Cerapoda was given a formal definition under thePhyloCode: "The smallest clade containingIguanodon bernissartensis Boulenger in Beneden, 1881,Pachycephalosaurus wyomingensis (Gilmore, 1931), andTriceratops horridus Marsh, 1889."[4]
The phylogenetic study of Fonseca and colleagues in 2024 recovered results similar to the previous analyses of Boyd and Herne and colleagues,[8][9] with thescelosaurids outside Ornithopoda and heterodontosaurids outside Neornithischia, while other aspects of relationships, like the placement ofChangmiania or the grouping within Ornithopoda were novel results. Their equal-weights results are below.[1]
| Ornithischia |
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