Penguins (order Sphenisciformes, family Spheniscidae) are a group of aquatic, flightless birds living almost exclusively in the southern hemisphere, especially in Antarctica. 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.
Among extant penguins, larger penguins inhabit colder regions, while smaller penguins are generally found in temperate or even tropical climates. Some prehistoric species attained enormous sizes, becoming as tall or as heavy as an adult human. These were not restricted to Antarctic regions; on the contrary, subantarctic regions harbored 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.
There are 17 to 19 known species worldwide, depending on whether the two Eudyptula species are counted as distinct. Although all penguin species are native to the southern hemisphere, they are not, contrary to popular belief, found only in cold climates, such as Antarctica. In fact, only a few species of penguin actually live so far south. Three species live in the tropics; one lives as far north as the Galpagos Islands (the Galapagos Penguin) and will occasionally cross the equator while feeding.
The largest species is the Emperor Penguin (Aptenodytes forsteri): adults average about 1.1 meters (3 ft 7 in) tall and weigh 35 kilograms (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 kilogram (2.2 lb). Generally larger penguins retain heat better, and thus inhabit colder regions, while smaller penguins are found in temperate or even tropical climates. The rarest type of penguin is the yellow-eyed penguin (Megadyptes antipodes) and is probably the most ancient of all living penguins: adults average about 65 cm tall and weigh 5-6 kilograms.
Most penguins feed on krill, fish, squid, and other forms of sealife caught while swimming underwater. They spend half of their life on land and half in the oceans.One of the most baffling forms of behavior of the penguin comes when a mother loses her chick, either due to its being unable to endure its first storm, or due to other reasons such as predators. When a mother loses its chick, they have been known to actually attempt to steal another mother's living chick- presumably in order to deal with the grief of the loss.
This behavior has amazed scientists, as it is an emotional outburst opposed to an instinctual behavior; something many wild animals do not exhibit when losing their young. Many have used this as prime evidence for decades that many animals have near human-like emotions and feelings, often for the sake of animal rights. Naturally, the other females in the penguin groups dislike this behavior and will help the defending mother keep her chick.
This behavior, however, might be better explained as a means for the female, or the male, to retain the full cooperation of the other parent in rearing the young, given that the bonding is monogamous; most likely there are differences between males and females in regards to the likelihood of chick-robbing and between species in relation to whether the monogamy is seasonal or permanent. Penguins seem to have no fear of humans, and have approached groups of explorers without hesitation.
The evolutionary history of penguins is poorly understood, as penguin fossils are rare. The oldest known fossil penguin species are the Waimanu, which lived in the early Paleocene epoch of New Zealand, about 62 million years ago. While they were not as well adapted to aquatic life as modern penguins (which first emerged in the Eocene epoch 40 million years ago), Waimanu were flightless and loon-like, with short wings adapted for deep diving.
These fossils prove that prehistoric penguins were already flightless and seagoing, so their origins probably reach as far back as 65 million years ago, before the extinction of the dinosaurs. Penguin ancestry beyond Waimanu is not well known, though some scientists (Mayr, 2005) think the penguin-like plotopterids (usually considered relatives of anhingas and cormorants) may actually be an early sister group of the penguins, and that penguins may have ultimately shared a common ancestor with the Pelecaniformes.