Anseriformes is an order of birds, dating back to the Late Cretaceous. It comprises about 150 living species in four extant families: Anhimidae (the screamers), Anseranatidae (the magpie goose), Dromornithidae (the mihirung), and Anatidae, the largest family, which includes over 140 species of waterfowl, among them the ducks, geese, and swans.
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).
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