Anseriformes - Evolution

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 represent early offshoots of the anseriform line, 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 and the huge and possibly carnivorous dromornithids were even more bizarre.