Aves in the context of "Ornithuran"

Feathers are epidermal growths that form a distinctive outer covering, or plumage, on both avian (bird) and some non-avian dinosaurs and other archosaurs. They are the most complex integumentary structures found in vertebrates and an example of a complex evolutionary novelty. They are among the characteristics that distinguish the extant birds from other living groups.

Although feathers cover most of the bird's body, they arise only from certain well-defined tracts on the skin. They aid in flight, thermal insulation, and waterproofing. In addition, coloration helps in communication and protection. The study of feathers is called plumology (or plumage science).

Incertae sedis (Latin for 'of uncertain placement') or problematica is a term used for a taxonomic group where its broader relationships are unknown or undefined. Alternatively, such groups are frequently referred to as "enigmatic taxa". In the system of open nomenclature, uncertainty at specific taxonomic levels is indicated by incertae familiae (of uncertain family), incerti subordinis (of uncertain suborder), incerti ordinis (of uncertain order) and similar terms.

Palaeognathae (/ˌpæliˈɒɡnəθi/; from Ancient Greek παλαιός (palaiós) 'old' and γνάθος (gnáthos) 'jaw') is an infraclass of birds, called paleognaths or palaeognaths, within the class Aves of the clade Archosauria. It is one of the two infraclasses of birds, the other being Neognathae, both of which form Neornithes. Palaeognathae contains five extant orders consisting of four flightless lineages (plus two that are extinct), termed ratites, and one flying lineage, the Neotropic tinamous. There are 47 species of tinamous, five of kiwis (Apteryx), three of cassowaries (Casuarius), one of emus (Dromaius) (another became extinct in historic times), two of rheas (Rhea) and two of ostriches (Struthio). Recent research has indicated that paleognaths are monophyletic but the traditional taxonomic split between flightless and flighted forms is incorrect; tinamous are within the ratite radiation, meaning flightlessness arose independently multiple times via parallel evolution.

There are three extinct groups that are undisputed members of Palaeognathae: the Lithornithiformes, the Dinornithiformes (moas) and the Aepyornithiformes (elephant birds), the latter two of which became extinct in the last 1250 years. There are other extinct birds which have been allied with the Palaeognathae by at least one author, but their affinities are a matter of dispute.

Neognathae (/niˈɒɡnəθiː/; from Ancient Greek νέος (néos) 'new, young' and γνάθος (gnáthos) 'jaw') is an infraclass of birds, called neognaths, within the class Aves of the clade Archosauria. 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 period, specifically during the Maastrichtian stage. As of 2025, the neognath genera from the latest Cretaceous supported by phylogenetic analyses include Asteriornis, Vegavis, Polarornis and Pujatopouli, 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 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 malleefowl (Leipoa ocellata) is a stocky ground-dwelling Australian bird about the size of a domestic chicken (to which it is distantly related). It is notable for the large nesting mounds constructed by the males and lack of parental care after the chicks hatch. It is the only living representative of the genus Leipoa, though the extinct giant malleefowl was a close relative.

The rufous-vented chachalaca (Ortalis ruficauda) is a member of an ancient group of birds of the family Cracidae, which are related to the Australasian mound builders. It inhabits northeast Colombia and northern Venezuela where it is called guacharaca, and the island of Tobago in Trinidad and Tobago where it is known as the cocrico and is one of the country's two national birds (being featured on the country's coat of arms). It is also found on Bequia and Union Island in the Grenadines where it may have been introduced.