Neornithischia or "new ornithischians" is a dinosaur clade within the order Ornithischia. Their closest relatives are the thyreophorans, and together with them, they form tha clade called Genasauria. Neornithischia is composed of basal neornithischians (hypsilophodonts), Marginocephalia (horned herbivorous dinosaurs like Triceratops), and Ornithopoda (like Parasaurolophus). The phylogenetic nomenclature of ornithischian dinosaurs defines neornithischians as "The largest clade containing Iguanodon bernissartensis and Triceratops horridus but not Ankylosaurus magniventris and Stegosaurus stenops." Neornithischians appeared first in the Early Jurassic period, and the group existed until the end of the Cretaceour Period. The main characteristic of neornithischians was the a thicker layer of asymmetrical enamel on the inside of their lower teeth. Due to this feature, the neornithischians were able to break down and consume tougher vegetation than other herbivore dinosaurs.
 Richard J. Butler; Paul Upchurch; David B. Norman (2008): The phylogeny of the ornithischian dinosaurs. Journal of Systematic Palaeontology, 6 (1): 1-40. doi: 10.1017/S1477201907002271.
 Madzia D, Arbour VM, Boyd CA, Farke AA, Cruzado-Caballero P, Evans DC. (2021): The phylogenetic nomenclature of ornithischian dinosaurs. PeerJ 9:e12362.  Clint A. Boyd (2015): The systematic relationships and biogeographic history of ornithischian dinosaurs. PeerJ. 3 (e1523). doi: 10.7717/peerj.1523.