Neognathae is a clade of birds, called neognaths, within the subclass Neornithes of the class Aves. Neognathae includes the majority of living birds; the exceptions being the tinamous and the flightless ratites, which belong instead to the sister taxon Palaeognathae. There are nearly 10,000 living species of neognaths.
The earliest fossils are known from the very end of the Cretaceous but molecular clocks suggest that neognaths originated sometime in the first half of the Late Cretaceous, about 90 million year ago. Since then, they have undergone adaptive radiation, producing the diversity of form, function, and behavior that exists today. Neognathae includes the order Passeriformes (perching birds), one of the largest orders of land vertebrates, containing some 60% of living birds. Passeriformes is twice as species-rich as Rodentia and about five times as species-rich as Chiroptera (bats), which are the two largest orders of mammals. Neognathae also contains some very small orders, often birds of unclear relationships like the hoatzin.
The neognaths have fused metacarpals, an elongate third finger, and 13 or fewer vertebrae. They differ from the Palaeognathae in features like the structure of their jawbones. Neognathae means "new jaws", but it seems that the supposedly "more ancient" paleognath jaws are among the few apomorphic (more derived) features of the palaeognaths, meaning that the respective jaw structure of these groups is not informative in terms of comparative evolution. A neognath-like palate is however seen in modern basal birds like Ichthyornis.