What is Neornithischia?

All genasaurians more closely related to Parasaurolophus walkeri, than to Ankylosaurus magniventris or Stegosaurus stenops. Neornithischia is the great branch of ornithischian dinosaurs that includes all the familiar beaked plant-eaters except the armoured ankylosaurs and stegosaurs. These dinosaurs inherited the basic feeding toolkit of Genasauria—most notably, teeth sat slightly inset from the outer edge of the jaws, creating space for cheeks that helped keep food in the mouth while chewing. But they also added an important new innovation of their own: a thick layer of enamel on the inner surfaces of their lower teeth, which wore out unevenly, creating sharp ridges that acted like natural serrated blades, allowing neornithischians to slice and grind tougher, more fibrous plants than earlier dinosaurs could manage. That improvement in dentition opened the door to a remarkable evolutionary radiation, which eventually gave rise to Marginocephalia and Ornithopoda—the latter of which would take oral processing to the next level.

Neornithischia and Cerapoda, as eventually defined, included pretty much the same critters. Technically, the latter should've been sunk into the former as a junior synonym because it was named a year later and, in fact, it was... by its own author Paul Sereno! However, after a little rejig, Neornithischia now houses Cerapoda (Marginocephalia and Thyreophora) plus a small handful of non-cerapod neornithischians.

Click here For DinoChecker's A-Z list of Neornithischians.