Penguins (order Sphenisciformes, family Spheniscidae) are a group of aquatic, flightless birds living almost exclusively in the southern hemisphere. Highly adapted for life in the water, penguins have countershaded dark and white plumage, and their wings have become flippers. Most penguins feed on krill, fish, squid, and other forms of sealife caught while swimming underwater. They spend about half of their life on land and half in the oceans.

Although all penguin species are native to the southern hemisphere, they are not found only in cold climates, such as Antarctica. In fact, only a few species of penguin live so far south. Several species are found in the temperate zone, and one species, the Galápagos Penguin, lives near the equator.

The largest living species is the Emperor Penguin (Aptenodytes forsteri): adults average about 1.1 m (3 ft 7 in) tall and weigh 35 kg (75 lb) or more. The smallest penguin species is the Little Blue Penguin (also known as the Fairy Penguin), which stands around 40 cm tall (16 in) and weighs 1 kg (2.2 lb). Among extant penguins, larger penguins inhabit colder regions, while smaller penguins are generally found in temperate or even tropical climates (see also Bergmann's Rule). Some prehistoric species attained enormous sizes, becoming as tall or as heavy as an adult human (see below for more). These were not restricted to antarctic regions; on the contrary, subantarctic regions harboured high diversity, and at least one giant penguin occurred in a region not quite 2,000 km south of the equator 35 mya , in a climate decidedly warmer than today.

Etymology

The word Penguin is thought by some to derive from the Welsh words pen (head) and gwyn (white),Oxford English Dictionary. Accessed 2007-03-21. applied to the Great Auk which had white spots in front of its eyes (although its head was black); or from an island off Newfoundland known as Pengwyn, due to its having a large white rock. (In the latter case, the name may also have come from Breton.) This theory is supported by the fact that penguins look remarkably like Great Auks in general shape.

It is also possible that penguin comes from the Latin pinguis, “fat”. This is supported by the fact that the corresponding words in most other languages (e.g., French pingouin, German Pinguin) have i instead of e as the first vowel. However, a Welsh i is often sound-shifted to an e in the English language.Fact: date=March 2007

Another theory states that the word is an alteration of “pen-wing”, with reference to the rudimentary wings of both Great Auks and penguins, but there is no evidence to support this.