Anseriformes is anorder ofbirds also known aswaterfowl that comprises about 180 livingspecies of birds in three families:Anhimidae (three species of screamers),Anseranatidae (the magpie goose), andAnatidae, the largest family, which includes over 170 species of waterfowl, among them theducks,geese, andswans. Most modern species in the order are highly adapted for an aquatic existence at the water surface. With the exception of screamers, males havepenises, a trait that has been lost in theNeoaves, the clade consisting of all other modern birds except thegalliformes andpaleognaths. Due to their aquatic nature, most species are web-footed.
Anseriformes are one of only two types of modern bird to be confirmed present during theMesozoic alongside the other dinosaurs, and in fact were among the very few birds to survive their extinction, along with their cousins, theGalliformes. These two groups only occupied two ecological niches during the Mesozoic, living in water and on the ground, while the toothedEnantiornithes were the dominant birds that ruled the trees and air. The asteroid that ended the Mesozoic destroyed all trees as well as animals in the open, a condition that took centuries[citation needed] to recover from. The Anseriformes and Galliformes are thought to have survived in the cover of burrows and water, and not to have needed trees for food and reproduction.[2]
The earliest known stem anseriform is thepresbyornithidTeviornis from theNemegt Formation ofMongolia.[3] Some members apparently surviving theKT extinction event, includingpresbyornithids, thought to be the common ancestors of ducks, geese, swans, andscreamers, the last group once thought to be Galliformes, but now genetically confirmed to be closely related to geese. The first known duck fossils start to appear about 34 million years ago.
Waterfowl are the best-known examples of sexually antagonistic genital coevolution in vertebrates, causing genital adaptations to coevolve in each sex to advance control over mating and fertilization. Sexually antagonistic coevolution (or SAC) occurs as a consequence ofsexual conflict between males and females, resulting in coevolutionary process that reduce fit, or that functions to decrease ease of having sex.[4]
The Anseriformes and theGalliformes (pheasants, etc.) belong to a common group, theGalloanserae. They are the most primitiveneognathous birds, and as such they should follow thePalaeognathae (ratites andtinamous) in bird classification systems. Several unusual extinct families of birds like the albatross-likepseudotooth birds and the giant flightlessgastornithids andmihirungs have been found to be stem-anseriforms based on common features found in the skull region, beak physiology and pelvic region.[5][6][7][8][9][10] The genusVegavis for a while was found to be the earliest member of the anseriformcrown group but a recent 2017 paper has found it to be just outside the crown group in the familyVegaviidae.[11] However, the monophyly of Vegaviidae was questioned by other researchers who described a nearly complete skull ofVegavis in 2025, supporting its placement within crown group Anseriformes.[1]
Below is the general consensus (prior to Torres et al. (2025)[1]) of the phylogeny of anseriforms and their stem relatives.[5][6][7][8][9][11]
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. Anatidae is traditionally divided into subfamilies Anatinae and Anserinae.[12] The Anatinae consists of tribesAnatini,Aythyini,Mergini andTadornini. The higher-order classification below follows aphylogenetic analysis performed by Mikko's Phylogeny Archive[13][14] and John Boyd's website.[15]
Order Anseriformes
?†ConflictoClaudia P. Tambussi et al. 2019 – tentatively placed here; possibly family Conflictonidae
†AnatalavisOlson & Parris 1987 (Late Cretaceous/Early Paleocene – Early Eocene) – includingNettapterornis; may belong in Anseranatidae or Conflictonidae
In addition, a considerable number of mainly Late Cretaceous andPaleogene 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 majorradiation 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 asPalaeopapia
Agnopterus (Late Eocene – Late Oligocene of Europe) – includesCygnopterus 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)
Studies of the mitochondrial DNA suggest the existence of four branches –Anseranatidae,Dendrocygninae,Anserinae andAnatinae – withDendrocygninae being a subfamily within the family Anatidae and Anseranatidae representing anindependent family.[19] The clade Somaterini has a single genusSomateria.
^abcTorres, Christopher R.; Clarke, Julia A.; Groenke, Joseph R.; Lamanna, Matthew C.; MacPhee, Ross D. E.; Musser, Grace M.; Roberts, Eric M.; O’Connor, Patrick M. (2025). "Cretaceous Antarctic bird skull elucidates early avian ecological diversity".Nature.638 (8049):146–151.doi:10.1038/s41586-024-08390-0.ISSN1476-4687.
^abAndors, A. (1992). "Reappraisal of the Eocene groundbirdDiatryma (Aves: Anserimorphae)".Science Series Natural History Museum of Los Angeles County.36:109–125.
^abMurrary, P.F; Vickers-Rich, P. (2004).Magnificent Mihirungs: The Colossal Flightless Birds of the Australian Dreamtime. Indiana University Press.
^Gonzalez, J.; Düttmann, H.; Wink, M. (2009). "Phylogenetic relationships based on two mitochondrial genes and hybridization patterns in Anatidae".Journal of Zoology.279 (3):310–318.doi:10.1111/j.1469-7998.2009.00622.x.
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