The largest living species is the emperor penguin (Aptenodytes forsteri):[6] on average, adults are about 1.1 m (3 ft 7 in) tall and weigh 35 kg (77 lb).

[26] The International Ornithologists' Union recognizes six genera and eighteen species:[27] Although the evolutionary and biogeographic history of Sphenisciformes is well-researched, many prehistoric forms are not fully described.

[3][28][29][30][excessive citations] The basal penguins lived around the time of the Cretaceous–Paleogene extinction event in the general area of southern New Zealand and Byrd Land, Antarctica.

[30] They swam on the surface using mainly their feet, but the wings were – as opposed to most other diving birds (both living and extinct) – already adapting to underwater locomotion.

An unnamed fossil from Argentina proves that, by the Bartonian (Middle Eocene), some 39–38 mya,[33] primitive penguins had spread to South America and were in the process of expanding into Atlantic waters.

The early Neogene saw the emergence of another morphotype in the same area, the similarly sized but more gracile Palaeospheniscinae, as well as the radiation that gave rise to the current biodiversity of penguins.

[35] The origin of the Spheniscinae lies probably in the latest Paleogene and, geographically, it must have been much the same as the general area in which the order evolved: the oceans between the Australia-New Zealand region and the Antarctic.

[28] Presumably diverging from other penguins around 40 mya,[28] it seems that the Spheniscinae were for quite some time limited to their ancestral area, as the well-researched deposits of the Antarctic Peninsula and Patagonia have not yielded Paleogene fossils of the subfamily.

Pygoscelis contains species with a fairly simple black-and-white head pattern; their distribution is intermediate, centred on Antarctic coasts but extending somewhat northwards from there.

In external morphology, these apparently still resemble the common ancestor of the Spheniscinae, as Aptenodytes' autapomorphies are, in most cases, fairly pronounced adaptations related to that genus' extreme habitat conditions.

As the former genus, Pygoscelis seems to have diverged during the Bartonian,[37] but the range expansion and radiation that led to the present-day diversity probably did not occur until much later; around the Burdigalian stage of the Early Miocene, roughly 20–15 mya.

They all lack carotenoid colouration and the former genus has a conspicuous banded head pattern; they are unique among living penguins by nesting in burrows.

This group probably radiated eastwards with the Antarctic Circumpolar Current out of the ancestral range of modern penguins throughout the Chattian (Late Oligocene), starting approximately 28 mya.

[28] The Megadyptes–Eudyptes clade occurs at similar latitudes (though not as far north as the Galápagos penguin), has its highest diversity in the New Zealand region, and represents a westward dispersal.

[28] The emergence of the Subantarctic lineage at the end of the Bartonian corresponds with the onset of the slow period of cooling that eventually led to the ice ages some 35 million years later.

What seems clear is that penguins belong to a clade of Neoaves (living birds except for paleognaths and fowl) that comprises what is sometimes called "higher waterbirds" to distinguish them from the more ancient waterfowl.

[40] A 2014 analysis of whole genomes of 48 representative bird species has concluded that penguins are the sister group of Procellariiformes,[41] from which they diverged about 60 million years ago (95% CI, 56.8–62.7).

Like the penguins, puffins have a white chest, black back and short stubby wings providing excellent swimming ability in icy water.

[49] Their eyes are adapted for underwater vision and are their primary means of locating prey and avoiding predators; in air it has been suggested that they are nearsighted, although research has not supported this hypothesis.

Calculations of the heat loss and retention ability of marine endotherms[52] suggest that most extant penguins are too small to survive in such cold environments.

[60] Living in colonies results in a high level of social interaction between birds, which has led to a large repertoire of visual as well as vocal displays in all penguin species.

[62] The relatively thick shell forms between 10 and 16% of the weight of a penguin egg, presumably to reduce the effects of dehydration and to minimize the risk of breakage in an adverse nesting environment.

[73][74] Major populations of penguins are found in Angola, Antarctica, Argentina, Australia, Chile, Namibia, New Zealand, and South Africa.

[75][76] Satellite images and photos released in 2018 show the population of 2 million in France's remote Ile aux Cochons has collapsed, with barely 200,000 remaining, according to a study published in Antarctic Science.

[98] Nicknamed Happy Feet, after the film of the same name, it was suffering from heat exhaustion and had to undergo a number of operations to remove objects like driftwood and sand from its stomach.

[99] Happy Feet was a media sensation, with extensive coverage on TV and the web, including a live stream that had thousands of views[100] and a visit from English actor Stephen Fry.

[102] Penguins are widely considered endearing for their unusually upright, waddling gait, swimming ability and (compared to other birds) lack of fear of humans.

The cartoon series Chilly Willy helped perpetuate this myth, as the title penguin would interact with Arctic or sub-Arctic species, such as polar bears and walruses.

Penguins have also appeared in a number of cartoons and television dramas, including Pingu, co-created by Otmar Gutmann and Erika Brueggemann in 1990 and covering more than 100 short episodes.

At the end of 2009, Entertainment Weekly put it on its end-of-the-decade "best-of" list, saying, "Whether they were walking (March of the Penguins), dancing (Happy Feet), or hanging ten (Surf's Up), these oddly adorable birds took flight at the box office all decade long.