Penguins are a group of aquatic, flightless birds. They live almost exclusively in the southern hemisphere, with only one species north of the equator, the Galapagos penguin. Penguins are very adaptable to life in the water. They cover dark and white feathers, and their wings develop into flippers. Most penguins feed on krill, fish, squid and other marine creatures caught swimming underwater. They spend half of their lives on land and the other half in the ocean.

Although almost all penguin species originate in the southern hemisphere, they are not only found in cold climates such as Antarctica. In fact, so far, only a few penguins live in the south. Several species have been found in temperate regions, one of which is the garpagos penguin, which lives near the equator.

The largest living species is Aptenodytes forsteri: the average adult is about 1.1 m (3 feet 7 inches) tall and weighs 35 kg (77 pounds) or more. The smallest penguin species is the eudptula minor, also known as the fairy tale penguin, which is about 40 cm (16 inches) high and weighs 1 kg (2.2 pounds). Among the extant penguins, the larger ones live in colder areas, while the smaller ones usually occur in temperate or even tropical climates (see also Bergman's law). Some prehistoric species have reached a huge scale, becoming as tall or as heavy as adult humans. These are not limited to Antarctica; on the contrary, there is a high degree of diversity in sub Antarctica, with at least one large Penguin 2000 km south of the equator 35 meters warmer than today.