The screamers are three South American bird species placed in family Anhimidae. They were thought to be related to the Galliformes because of similar bills, but are more related to ducks, and most closely related to the magpie goose. The clade is exceptional within the living birds in lacking uncinate processes of ribs. The three species are, the horned screamer, the southern screamer or crested screamer and the northern screamer or black-necked screamer. A penis is absent in the males, and the birds' skin has a layer about a quarter of an inch thick, filled with small bubbles of air, which produce a crackling sound when pressed.
