Neornithischia


Neornithischia 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.

Classification

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. 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: