Anseriforms represent an ancient lineage, one of the earliest in the evolution of modern birds, going as far back as the Cretaceous period more than 65 million years ago. The rich fossil record of modern waterfowl starts in the Late Eocene epoch (37 to 33.7 million years ago). Screamers (Anhimidae) and magpie goose (Anseranatidae) are primitive families.The third family, Waterfowl (Anatidae), by far the most numerous, differentiated along two main lines:

The first line  became the swans and typical geese (subfamily Anserinae), large-bodied, long-lived, slow-breeding birds, with prolonged pair and family bonds and associated parental care of the young ; sexes similar in plumage, voice; behaviour which includes “triumph” ceremony and precopulatory head dipping.

The second line, characterized by most of the ducks, has favoured small-bodied, short-lived birds having brief pair bonds and minimal care of the young, correlated with prolific production of young. This second line includes the following subfamilies: (Anatinae) Dabbling ducks, perching ducks and atypical geese;
(Tadorninae) Shelgeese, shelducks steamer ducks, Egyptian Goose;
(Plectropterinae) Spur-winged geese, previously classified as Tadorninae;
(Merginae) Sea ducks, mostly divers in salt water;
(Dendrocygninae) Whistling ducks;
(Oxyurinae)  Stiff-tailed ducks.

anseriform. (2011). Encyclopædia Britannica Ultimate Reference Suite.  Chicago: Encyclopædia Britannica. Annotated classification by Geoffrey Vernon, Townsend Matthews and Frank Gill.

http://en.wikipedia.org/wiki/Anseriformes