No definition has been proposed. Marsh (1873) erected this taxon to include Ichthyornis and Apatornis, taxa that do not appear to be each other’s closest relatives (Clarke 2004). Marsh and others have used Odontornithes to encompass a paraphyletic clade of toothed birds including Hesperornithiformes and Ichthyornithiformes. Given that some of the material Marsh described under this taxon may be eventually allied even farther afield within Aves (Clarke 2004), it is just as well that the taxon has fallen from use.