The type species, N. adhicaster, was first described by A. Weithofer in 1887 on the basis of fragmentary fossils from the Eocene deposits of the Quercy Phosphorites Formation.[2] Weithofer did not designate a type specimen,[3] simply describing a lower jaw. This material was later described in more detail by Pierre Revilliod in 1920, offering the holotype the number QW6627. He described additional material, and classified it within three species: N. adhicaster, N. gerzei, N. marandati, N. planifrons and N. grandis.