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Neognathae (; ) is an infraclass of , called neognaths, within the class Aves of the clade Archosauria. Neognathae includes the majority of living birds; the exceptions being the and the flightless , which belong instead to the sister taxon Palaeognathae. There are nearly 10,000 living species of neognaths.
The earliest are known from the very end of the Cretaceous with the oldest known members being Teviornis and Vegavis, but molecular clocks suggest that neognaths originated sometime in the first half of the Late Cretaceous, about 90 million years 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 and about five times as species-rich as bat (bats), which are the two largest orders of . Neognathae also contains some very small orders, often birds of unclear relationships like the hoatzin.
The neognaths have fused , an elongate third finger, and 13 or fewer . 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 (more derived) features of the palaeognaths, meaning that the respective jaw structure of these groups is not informative in terms of comparative evolution. However, a neognath-like palate is also present in Ornithurae birds like Ichthyornis.
Neognathae is now universally accepted to subdivide into two lineages, the "fowl" clade Galloanseres and the Neoaves (sometimes called "higher neognaths"). The formal PhyloCode definition given to Neognathae by George Sangster and colleagues in 2022 is "the least inclusive crown clade containing Gallus gallus and Passer domesticus".
The subdivisions of the latter are still not well resolved, but several monophyletic lineages have been proposed, such as the Mirandornithes, Cypselomorphae, Metaves, and Coronaves. Although groups such as the former two (uniting a few closely related orders) are robustly supported, this cannot be said for the groups Metaves and Coronaves for which there is no material evidence at present, while the Mesozoic record of Neognathae is at present utterly devoid of birds that should have been present if these proposed clades were real.For a draft phylogeny of Neoaves that is based on a review of massive amounts of published sources, and probably rather close to "the real thing", see Mindell et al. (2005)
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Neognathae comprises 39 Neontology orders and are categorized as:
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