Fowl

Fowl is a word for birds in general but usually refers to birds belonging to one of two biological orders, namely the gamefowl or landfowl (Galliformes) and the waterfowl (Anseriformes). Studies of anatomical and molecular similarities suggest these two groups are close evolutionary relatives; together, they form the fowl clade which is scientifically known as Galloanserae (initially termed Galloanseri). This clade is also supported by morphological and DNA sequence data as well as retrotransposon presence/absence data.

Terminology
As opposed to "fowl", "poultry" is a term for any kind of domesticated bird or bird captive-raised for eggs, or feathers; ostriches, for example, are sometimes kept as poultry, but are neither gamefowl nor waterfowl. In colloquial speech, however, the term "fowl" is often used near-synonymously with "poultry" or even "bird", and many languages do not distinguish between "poultry" and "fowl". Nonetheless, the fact that Galliformes and Anseriformes most likely form a monophyletic group makes a distinction between "fowl" and "poultry" warranted.

The historic difference is due to the Germanic/Latin split word pairs characteristic of Middle English; the word 'fowl' is of Germanic origin (cf. Old English "Fugol", German Vogel, Danish Fugl), whilst poultry is of Latin via Norman French origin.

Characteristics
While they are quite diverse ecologically and consequently, in an adaptation to their different lifestyles, also morphologically and ethologically, there are still some features which unite water- and landfowl. Many of these, however, are plesiomorphic for Neornithes as a whole, and are also shared with paleognaths.
 * Galloanserae are very prolific; they regularly produce clutches of more than 5 or even more than 10 eggs, which is a lot for such sizeable birds. For example birds of prey and pigeons rarely lay more than two eggs.
 * While most living birds are monogamous, at least for a breeding season, many Galloanserae are notoriously polygynous or polygamous. To ornithologists, this is particularly well known in dabbling ducks, where the males literally band together occasionally to "gang rape" unwilling females. The general public is probably most familiar with the polygynous habits of domestic chicken, where usually one or two roosters are kept with a whole flock of females.
 * Hybridization is extremely frequent in Galloanserae, and genera, not usually known to produce viable hybrids in birds, can be brought to interbreed with comparative ease. Guineafowl have successfully produced hybrids with domestic fowl and Blue Peafowl, to which they are not particularly closely related as Galliformes go. This is an important factor complicating mtDNA sequence-based research on their relationships. The Mallards of North America, for example, are apparently mostly derived from some males which arrived from Siberia, settled down, and mated with American Black Duck ancestors. See also Gamebird hybrids.
 * Galloanserae young are remarkably precocious. Anseriform young are able to swim and dive a few hours after hatching, and the hatchlings of mound-builders are fully feathered and even able to fly for prolonged distances as soon as they emerge from the nest mound.

Systematics and evolution
From the limited fossils that have to date been recovered, the conclusion that they were already widespread—the predominant group of modern birds—by end of the Cretaceous is generally accepted nowadays. Fossils such as Vegavis indicate that essentially modern waterfowl, albeit belonging to a nowadays extinct lineage, were contemporaries of the (non-avian) dinosaurs. As opposed to the morphologically fairly conservative Galliformes, the Anseriformes have adapted to filter-feeding and are characterized by a large number of autapomorphies related to this lifestyle. The extremely advanced feeding systems of the Anseriformes, together with similarities of the early anseriform Presbyornis to shorebirds, had formerly prompted some scientists to ally Anseriformes with Charadriiformes instead. However, as strong support for the Galloanserae has emerged in subsequent studies, the fowl clade continues to be accepted as a genuine evolutionary lineage by the vast majority of scientists.

Apart from the living members, the Gastornithidae are probably a prehistoric member of the Galloanserae.