The Pelecaniformes are an order of medium-sized and large waterbirds found worldwide. As traditionally—but erroneously—defined, they encompass all birds that have feet with all four toes webbed. Hence, they were formerly also known by such names as totipalmates or steganopodes. Most have a bare throat patch, and the nostrils have evolved into dysfunctional slits, forcing them to breathe through their mouths. They also have a pectinate nail on their longest toe. This is shaped like a comb and is used to brush out and separate their feathers. They feed on fish, squid, or similar marine life. Nesting is colonial, but individual birds are monogamous. The young are altricial, hatching from the egg helpless and naked in most. They lack a brood patch.
Otidae is a clade that includes the superorders Otidimorphae and Strisores. It was identified in 2014 by genome analysis. Earlier it was thought that Strisores was closely related to birds such as pigeons, flamingos, tropicbirds, and the sunbittern and kagu in the taxon Metaves, but subsequent work has provided evidence that Metaves is polyphyletic. Although analyses of genome data provided relatively high support for monophyly of Otidae, indicating that it occupies a basal branch of the clade Passerea, other analyses of large data matrices have not recovered a clade comprising Otidimorphae and Strisores, raising questions about the monophyly of Otidae.
The Phaethontiformes are an order of birds. They contain one extant family, the tropicbirds (Phaethontidae), and one extinct family Prophaethontidae from the early Cenozoic. Several fossil genera have been described, with well-preserved fossils known as early as the Paleocene. The group's origins may lie even earlier if the enigmatic waterbird Novacaesareala from the latest Cretaceous or earliest Paleocene of New Jersey is considered a tropicbird.
Neoaves is a clade that consists of all modern birds with the exception of Palaeognathae and Galloanserae. Almost 95% of the roughly 10,000 known species of extant birds belong to the Neoaves.
Mirandornithes is a clade that consists of flamingos and grebes. Many scholars use the term Phoenicopterimorphae for the superorder containing flamingoes and grebes.
Aequornithes, or core water birds, are defined as "the least inclusive clade containing Gaviidae and Phalacrocoracidae".
The order Falconiformes is represented by the extant family Falconidae and a handful of enigmatic Paleogene species. Traditionally, the other bird of prey families Cathartidae, Sagittariidae (secretarybird), Pandionidae (ospreys), Accipitridae (hawks) were classified in Falconiformes. A variety of comparative genome analysis published since 2008, however, found that falcons are part of a clade of birds called Australaves, which also includes seriemas, parrots and passerines. Within Australaves falcons are more closely related to the parrot-passerine clade (Psittacopasserae), which together they form the clade Eufalconimorphae. The hawks and vultures occupy a basal branch in the clade Afroaves in their own clade Accipitrimorphae, closer to owls and woodpeckers.
Psittacopasseres is a taxon of birds consisting of the Passeriformes and Psittaciformes (parrots). Per Ericson and colleagues, in analysing genomic DNA, revealed a lineage comprising passerines, psittacines and Falconiformes. The group was proposed following an alignment of nuclear intron sequences by Shannon Hackett et al. in 2008. It was formally named as Psittacopasserae in a 2011 Nature Communications article by Alexander Suh and other authors working with Jürgen Schmitz's group, based on genetic analysis of the insertion of retroposons into the genomes of key avian lineages over the course of evolution during the Mesozoic Era.
Eurypygiformes is an order formed by the kagus, comprising two species in the family Rhynochetidae endemic to New Caledonia, and the sunbittern from the tropical regions of the Americas. Its closest relatives appear to be the tropicbirds of the tropical Atlantic, Indian, and Pacific oceans.
Strisores, sometimes called nightbirds, is a clade of birds that includes the living families and orders Caprimulgidae, Nyctibiidae (potoos), Steatornithidae (oilbirds), Podargidae (frogmouths), Apodiformes, as well as the Aegotheliformes (owlet-nightjars) whose distinctness was only recently realized. The Apodiformes and the Aegotheliformes form the Daedalornithes.
Columbea is a clade suggested by genome analysis that contains Columbiformes, Pteroclidae (sandgrouse), Mesitornithidae (mesites) and Mirandornithes. Until their recent placement as the sister taxon to Passerea, in the last decade various genetic analysis found them to be in the obsolete clade Metaves.
Passerea is a clade of neoavian birds that was proposed by Jarvis et al. (2014). Their genomic analysis recovered two major clades within Neoaves, Passerea and Columbea, and concluded that both clades appear to have many ecologically driven convergent traits.
Otidimorphae is a clade of birds that contains the orders Cuculiformes (cuckoos), Musophagiformes (turacos), and Otidiformes (bustards) identified in 2014 by genome analysis. While the bustards seem to be related to the turacos, other genetic studies have found the cuckoos to be closer to the bustards than the turacos are.
Phaethoquornithes is a clade of birds that contains Eurypygimorphae and Aequornithes, which was first recovered by genome analysis in 2014. Members of Eurypygimorphae were originally classified in the obsolete group Metaves, and Aequornithes were classified as the sister taxon to Musophagiformes or Gruiformes.
Eucavitaves is a clade that contains the order Trogoniformes (trogons) and the clade Picocoraciae. The name refers to the fact that the majority of them nest in cavities.
Cavitaves is a clade that contain the order Leptosomiformes and the clade Eucavitaves. The name refers to the fact that the majority of them nest in cavities.
Columbimorphae is a clade discovered by genome analysis that includes birds of the orders Columbiformes, Pterocliformes (sandgrouse), and Mesitornithiformes (mesites). Previous analyses had also recovered this grouping, although the exact relationships differed. Some studies indicated a sister relationship between sandgrouse and pigeons while other studies favored a sister grouping of mesites and sandgrouse instead.
Picodynastornithes is a clade that contains the orders Coraciiformes and Piciformes. This grouping also has current and historical support from molecular and morphological studies.
Columbaves is a clade that contains Columbimorphae and Otidimorphae discovered by genomic analysis by Prum et al. (2015). This conflicts with the Columbea and Otidae hypotheses which Mirandornithes are the sister taxon to Columbimorphae and Cypselomorphae the sister taxon to Otidimorphae, respectively, found by Jarvis et al. (2014). Neither hypothesis supports the two subdivisions of Metaves and Coronoaves as previous studies had found.
Aequorlitornithes is a clade of waterbirds recovered in a comprehensive genomic systematic study using nearly 200 species in 2015. It contains the clades Charadriiformes, Mirandornithes and Phaethoquornithes. Previous studies have found different placement for the clades in the tree.
