Anseriformes is an order of birds that comprises about 180 living species in three families: Anhimidae (the screamers), Anseranatidae (the magpie goose), and Anatidae, the largest family, which includes over 170 species of waterfowl, among them the ducks, geese, and swans. In fact, these living species are all included in Anatidae except for the three screamers and the magpie goose. All species in the order are highly adapted for an aquatic existence at the water surface. The males, except for the screamers, also have a penis, a trait that has disappeared in Neoaves. All are web-footed for efficient swimming (although some have subsequently become mainly terrestrial).
Black bellied whistling duck resting dendrocygna autumnalis anseriformes family anatidae
Evolution
The earliest known Anseriform is the recently discovered Vegavis, which lived during the Cretaceous period. It is thought that the Anseriformes originated when the original Galloanserae (the group to which Anseriformes and Galliformes belong) split into the two main lineages. The extinct dromornithids may possibly represent early offshoots of the anseriform line, if they aren't stem-Galliformes instead, and so maybe Gastornis (if it is an Anseriform). The ancestors of the Anseriformes developed the characteristic bill structure that they still share. The combination of the internal shape of the bill and a modified tongue acts as a suction pump to draw water in at the tip of the bill and expel it from the sides and rear; an array of fine filter plates called lamellae traps small particles, which are then licked off and swallowed.
All Anseriformes have this basic structure, but many have subsequently adopted alternative feeding strategies: geese graze on plants, the saw-billed ducks catch fish; even the screamers, which have bills that seem on first sight more like those of the game birds, still have vestigal lamellae. The prehistoric wading presbyornithids were even more bizarre.
Taxonomy
The Anseriformes and the Galliformes (pheasants, etc.) are the most primitive neognathous birds, and should follow ratites and tinamous in bird classification systems.
Anatidae systematics, especially regarding placement of some "odd" genera in the dabbling ducks or shelducks, is not fully resolved. See the Anatidae article for more information, and for alternate taxonomic approaches. Some unusual groups, such as the extinct Gastornithidae and Dromornithidae, are often found to be at the base of the Anseriformes family tree, or at least their closest relatives.
Anatidae is traditionally divided into subfamilies Anatinae and Anserinae. The Anatinae consists of tribes Anatini, Aythyini, Mergini and Tadornini.
Systematics
The higher-order classification below follows a phylogenetic analysis performed by Angolin, 2007, Mikko's Phylogeny Archive and John Boyd's website.
Order Anseriformes
Family †Gastornithidae?: "diatrymas"
Family ?†Dromornithidae Fürbringer 1888 (mihirungs)
Genus †Barawertornis tedfordi Rich 1979
Genus †Genyornis newtoni Sterling & Ziets 1896
Genus †Ilbandornis Rich 1979
Genus †Bullockornis planei Rich 1979 (Demon-Duck of Doom)
In addition, a considerable number of mainly Late Cretaceous and Paleogene fossils have been described where it is uncertain whether or not they are anseriforms. This is because almost all orders of aquatic birds living today either originated or underwent a major radiation during that time, making it hard to decide whether some waterbird-like bone belongs into this family or is the product of parallel evolution in a different lineage due to adaptive pressures.
"Presbyornithidae" gen. et sp. indet. (Barun Goyot Late Cretaceous of Udan Sayr, Mongolia) – Presbyornithidae?
UCMP 117599 (Hell Creek Late Cretaceous of Bug Creek West, USA)
Petropluvialis (Late Eocene of England) – may be same as Palaeopapia
Agnopterus (Late Eocene – Late Oligocene of Europe) – includes Cygnopterus lambrechti
"Headonornis hantoniensis" BMNH PAL 4989 (Hampstead Early Oligocene of Isle of Wight, England) – formerly "Ptenornis"
Palaeopapia (Hampstead Early Oligocene of Isle of Wight, England)
"Anas" creccoides (Early/Middle Oligocene of Belgium)
"Anas" skalicensis (Early Miocene of "Skalitz", Czech Republic)
"Anas" risgoviensis (Late Miocene of Bavaria, Germany)
Living Anseriformes based on the work by John Boyd.
Molecular studies
Studies of the mitochnodrial DNA suggest the existence of four branches – Anseranatidae, Dendrocygninae, Anserinae and Anatinae – with Dendrocygninae being a subfamily within the family Anatidae and Anseranatidae representing an independent family. The clade Somaterini has a single genus Somateria.
Cited texts
Agnolin, F. (2007) Brontornis burmeisteri Moreno & Mercerat, un Anseriformes (Aves) gigante del Mioceno Medio de Patagonia, Argentina. Revista del Museo Argentino de Ciencias Naturales. 9:15–25.
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
Livezey, B. C. & Zusi, R. L. (2007) Higher-order phylogeny of modern birds (Theropoda, Aves: Neornithes) based on comparative anatomy. II. Analysis and discussion. Zoological Journal of the Linnen Society. 149: 1–95.
Murray, P. F. & Vickers-Rich, P. (2004) Magnificent Mihirungs: The Colossal Flightless Birds of the Australian Dreamtime. Indiana University Press.
