One of the two recognized superorders of living birds that comprise the subclass Neornithes of the class Aves. The Neognathae are characterized as flying birds with the absence of teeth in both jaws, fully developed wings, keeled bony sternum, strong synsacrum fused with the pelvic girdle, and caudal vertebrae fused into a pygostyle; modifications in these conditions occurred in secondary flightless birds.