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.
[1]
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.
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Basal divergences of modern birds in the Sibley–Ahlquist taxonomy
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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.
[2]
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.
[3]
Classification
See also
References
-
^ Sibley & Ahlquist (1990)
-
^ Sibley and Ahlquist (1988)
-
^ Clarke et al.' (2005)
- 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