Neornithischia was first named by Cooper in 1985 and defined as "all genasaurians more closely related to Parasaurolophus walkeri than to Ankylosaurus magniventris or Stegosaurus stenops".
The suborder Neornithischia was initially introduced by Cooper in 1985, characterized as comprising all genasaurians that are more closely allied with Parasaurolophus walkeri compared to Ankylosaurus magniventris or Stegosaurus stenops.