Hesperornithes is an extinct and highly specialized clade of Cretaceous toothed birds. Hesperornithine birds, apparently limited to former aquatic habitats in the Northern Hemisphere, include genera such as Hesperornis, Parahesperornis, Baptornis, Enaliornis, and probably Potamornis, all strong-swimming predatory waterbirds. Many, if not all species were completely flightless. The largest known hesperornithine, described in 1999 and named Canadaga arctica, may have reached a maximum adult length of over 1.5 meters (five feet).