Biology:Sibley–Ahlquist taxonomy of birds

Short description: Proposed classification system of birds

The Sibley–Ahlquist taxonomy is a bird taxonomy proposed by Charles Sibley and Jon E. Ahlquist. It is based on DNA–DNA hybridization studies conducted in the late 1970s and throughout the 1980s.

DNA–DNA hybridization is among a class of comparative techniques in molecular biology that produce distance data (versus character data) and that can be analyzed to produce phylogenetic reconstructions only using phenetic tree-building algorithms. In DNA–DNA hybridization, the percent similarity of DNA between two species is estimated by the reduction in hydrogen bonding between nucleotides of imperfectly complemented heteroduplex DNA (i.e., double stranded DNAs that are experimentally produced from single strands of two different species), compared with perfectly matched homoduplex DNA (both strands of DNA from the same species).

Characteristics

The classification appears to be an early example of cladistic classification because it codifies many intermediate levels of taxa: the "trunk" of the family tree is the class Aves, which branches into subclasses, which branch into infraclasses, and then "parvclasses", superorders, orders, suborders, infraorders, "parvorders", superfamilies, families, subfamilies, tribes, subtribes and finally genera and species. However the classification study did not employ modern cladistic methods, as it relies strictly on DNA-DNA hybridization as the sole measure of similarity.

The Sibley–Ahlquist arrangement differs greatly from the more traditional approach used in the Clements taxonomy.

Neornithes   Palaeognathae      Neognathae    Other birds   Galloanseri    Anseriformes          Galliformes     Craciformes

Basal divergences of modern birds in the Sibley–Ahlquist taxonomy

Showing major changes from Clements, the Sibley–Ahlquist orders are as follows:

• Enlarged Struthioniformes replaces the ratite orders Rheiformes (rheas), Casuariiformes (cassowaries and emus), and Apterygiformes (kiwis) and Struthioniformes (ostriches).
• Tinamiformes (tinamous) is unchanged.
• A greatly enlarged Ciconiiformes includes the previous Sphenisciformes (penguins), Gaviiformes (divers), Podicipediformes (grebes), Procellariiformes (tubenoses), Pelecaniformes (pelicans and allies), Ciconiiformes (storks and allies), Falconiformes (birds of prey), Charadriiformes (waders, gulls, terns, and auks), and the family Pteroclidae (sandgrouse).
• Anseriformes (ducks and allies) is unchanged.
• Modified Galliformes landfowl. Chachalacas moved to Craciformes.
• New Craciformes chachalacas etc. Previously part of Galliformes.
• New Ralliformes rails and crakes. Previously part of Gruiformes
• Modified Gruiformes Cranes. Rails and button-quails moved to Ralliformes and Turniciformes, respectively.
• New Turniciformes button-quails etc. Previously part of Gruiformes.
• Modified Columbiformes doves. Sandgrouse moved to Ciconiiformes.
• Psittaciformes cockatoos and parrots unchanged.
• New Musophagiformes turacos. Previously part of Cuculiformes.
• Modified Cuculiformes cuckoos. Turacos moved to Musophagiformes.
• Modified Strigiformes owls. Enlarged to include Caprimulgiformes (nightjars, owlet-nightjars, frogmouths, oilbirds, potoos).
• Modified Apodiformes swifts. Hummingbirds moved to Trochiliformes.
• New Trochiliformes hummingbirds. Previously part of Apodiformes.
• Coliiformes mousebirds unchanged.
• Trogoniformes trogons unchanged.
• Modified Coraciiformes rollers.
• New Upupiformes Hoopoe. Previously part of Coraciiformes.
• New Bucerotiformes hornbills. Previously part of Coraciiformes.
• New Galbuliformes jacamars and puffbirds. Previously part of Piciformes.
• Modified Piciformes woodpeckers
• Passeriformes perching birds unchanged.

Some of these changes are minor adjustments. For instance, instead of putting the swifts, treeswifts, and hummingbirds in the same order that includes nothing else, Sibley and Ahlquist put them in the same superorder that includes nothing else, consisting of one order for the hummingbirds and another for the swifts and treeswifts. In other words, they still regard the swifts as the hummingbirds' closest relatives.

Other changes are much more drastic. The penguins were traditionally regarded as distant from all other living birds. For instance, Wetmore put them in a superorder by themselves, with all other non-ratite birds in a different superorder. Sibley and Ahlquist, though, put penguins in the same superfamily as divers (loons), tubenoses, and frigatebirds. According to their phylogenetic analysis, penguins are closer to those birds than herons are to storks.

The Galloanseres (waterfowl and landfowl) has found widespread acceptance. The DNA evidence of Sibley–Ahlquist for the monophyly of the group is supported by the discovery of the fossil bird Vegavis iaai, an essentially modern but most peculiar waterfowl that lived near Cape Horn some 66-68 million years ago, still in the age of the dinosaurs.

Classification

Parvclass	Superorder	Order	Families	Note on current status
Infraclass Eoaves
Ratitae		Struthioniformes	Struthionidae Rheidae Casuariidae Apterygidae
		Tinamiformes	Tinamidae
Galloanserae	Gallomorphae	Craciformes	Cracidae Megapodiidae	Families included in Galliformes.
		Galliformes	Phasianidae Numididae Odontophoridae
	Anserimorphae	Anseriformes	Anhimidae Anseranatidae Dendrocygnidae Anatidae
Infraclass Neoaves
Turnicae		Turniciformes	Turnicidae	Included in Charadriiformes.
Picae		Piciformes	Indicatoridae Picidae Megalaimidae Lybiidae Ramphastidae
Coraciae	Galbulimorphae	Galbuliformes	Galbulidae Bucconidae	Families included in Piciformes by most authorities.
	Bucerotimorphae	Bucerotiformes	Bucerotidae Bucorvidae
		Upupiformes	Upupidae Phoeniculidae Rhinopomastidae	Families included in Bucerotiformes by most authorities.
	Coraciimorphae	Trogoniformes	Trogonidae
		Coraciiformes	Coraciidae Brachypteraciidae Leptosomidae Momotidae Todidae Alcedinidae Halcyonidae Cerylidae Meropidae
Coliae		Coliiformes	Coliidae
Passerae	Cuculimorphae	Cuculiformes	Cuculidae Centropodidae Coccyzidae Opisthocomidae Crotophagidae Neomorphidae	Opisthocomidae now place in own order, Opisthocomiformes.
	Psittacimorphae	Psittaciformes	Psittacidae
	Apodimorphae	Apodiformes	Apodidae Hemiprocnidae	Included in Caprimulgiformes by most authorities. Otherwise in enlarged Apodiformes.
		Trochiliformes	Trochilidae
	Strigimorphae	Musophagiformes	Musophagidae
		Strigiformes	Tytonidae Strigidae Aegothelidae Podargidae Batrachostomidae Steatornithidae Nyctibiidae Eurostopodidae Caprimulgidae	Strigiformes restricted to owls (Tytonidae, Strigidae) Other families are placed in Caprimulgiformes.
	Passerimorphae	Columbiformes	Raphidae Columbidae
		Gruiformes	Eurypygidae Otididae Gruidae Aramidae Heliornithidae Psophiidae Cariamidae Rhynochetidae Rallidae Mesitornithidae	Gruiformes found to be polyphyletic: Eurypygidae and Rhynochetidae now in Eurypygiformes; Odtidae now in Otidiformes; Cariamidae now in Cariamiformes; Mesitornithidae now in Mesitornithiformes.
		Ciconiiformes	Pteroclidae Thinocoridae Pedionomidae Scolopacidae Rostratulidae Jacanidae Chionidae Pluvianellidae Burhinidae Charadriidae Glareolidae Laridae Accipitridae Sagittariidae Falconidae Podicipedidae Phaethontidae Sulidae Anhingidae Phalacrocoracidae Ardeidae Scopidae Phoenicopteridae Threskiornithidae Pelecanidae Ciconiidae Fregatidae Spheniscidae Gaviidae Procellariidae	Ciconiiformes found to be polyphyletic and now restricted to storks (Ciconiidae). The other families are distributed between: Pterocliformes (Pteroclidae) Charadriiformes (Thinocoridae through Laridae) Accipitriformes (Accipitridae, Sagittariidae) Falconiformes (Falconidae) Podicipediformes (Podicipedidae) Phaethontiformes (Phaethontidae) Suliformes (Sulidae, Anhingidae, Phalacrocoracidae, Fregatidae) Pelecaniformes (Ardeidae, Scopidae, Threskiornithidae, Pelecanidae) Phoenicopteriformes (Phoenicopteridae) Sphenisciformes (Spheniscidae) Gaviiformes (Gaviidae) Procellariiformes (Procellariidae)
		Passeriformes	Acanthisittidae Pittidae Eurylaimidae Philepittidae Tyrannidae Thamnophilidae Furnariidae Formicariidae Conopophagidae Rhinocryptidae Climacteridae Menuridae Ptilonorhynchidae Maluridae Meliphagidae Pardalotidae Petroicidae Irenidae Orthonychidae Pomatostomidae Laniidae Vireonidae Corvidae Callaeatidae Picathartidae Bombycillidae Cinclidae Muscicapidae Sturnidae Sittidae Certhiidae Paridae Aegithalidae Hirundinidae Regulidae Pycnonotidae Hypocoliidae Cisticolidae Zosteropidae Sylviidae Alaudidae Nectariniidae Melanocharitidae Paramythiidae Passeridae Fringillidae

See also

• Molecular phylogenetics
• Phylogenetic nomenclature
• Charles Sibley
• Sibley–Monroe checklist
• List of birds (based on the Clements taxonomy)

References

• Clarke, J.A.; Tambussi, C.P.; Noriega, J.I.; Erickson, G.M. & Ketcham, R.A. (2005): Definitive fossil evidence for the extant avian radiation in the Cretaceous. Nature 433: 305–308. doi:10.1038/nature03150 PDF fulltext Supporting information
• Sibley, Charles Gald & Ahlquist, Jon Edward (1990): Phylogeny and classification of birds. Yale University Press, New Haven, Conn.
• On the Phylogeny and Classification of Living Birds, by Charles G. Sibley
• The Early History of Modern Birds Inferred from DNA Sequences of Nuclear and Mitochondrial Ribosomal Genes, by Marcel van Tuinen, Charles G. Sibley, and S. Blair Hedges
• Sibley's Classification of Birds, by Eric Salzman, Birding, December 1993. The Web version lacks the illustrations, which show parts of the family tree, and includes only a partial bibliography, but adds a sequence down to the tribe level with detail on intermediate taxa (especially for the passerines). Archived version