Ducks and geese belong to one of the few bird lines that outlived the dinosaurs
When the asteroid ended the age of dinosaurs, it flattened forests and wiped out the tree-dwelling toothed birds that then ruled the skies. The ancestors of ducks, geese and swans pulled through, probably sheltering in water and burrows. Their order, the Anseriformes, is one of only two modern bird groups confirmed from that era.
Today the order has 178 living species in three families. Two are tiny: the screamers, with three species, and the magpie goose, alone in its family. Everything else, 174 species of ducks, geese and swans, sits in the family Anatidae. Most are built for life on the water's surface and have webbed feet.
Their survival story is tied to lifestyle. During the Mesozoic, the ancestors of waterfowl and their cousins the Galliformes, the pheasant group, lived only on the ground and in water, while the dominant Enantiornithes held the trees and air. The impact destroyed trees and exposed animals, and some models suggest greenhouse effects lingered for thousands of years. Birds that did not need trees for food or nesting had an edge. The oldest known relative of the line, Teviornis, comes from Mongolia, and recognisable duck fossils appear about 34 million years ago.
The family tree holds surprises. Screamers were once classed with the Galliformes, but genetics shows they are close kin of geese. Some bizarre extinct birds turn out to be early offshoots too, including the albatross-like pseudotooth birds and giant flightless gastornithids, identified from features of the skull, beak and pelvis. The ancient Vegavis keeps shifting position: a 2025 study of a nearly complete skull placed it inside the modern group, and a 2026 reanalysis said it can only be called a neognath of uncertain affinities.
Waterfowl are also biologically unusual. Unlike almost all other modern birds, male waterfowl other than screamers have penises, a feature lost in the Neoaves. They are the best-known vertebrate example of sexually antagonistic coevolution, in which male and female anatomy evolve against each other in a contest over control of mating and fertilization.
Source: Anseriformes
