Penguin
Kingdom: Animalia


Phylum: Chordata
Class: Aves
Infraclass: Neognathae
Order: Sphenisciformes
Sharpe, 1891
Family: Spheniscidae
Bonaparte, 1831

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.




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 (Eudyptula minor), 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 etymology of the word "penguin" is highly disputed. The English word is not apparently of French[1], nor of Breton[2] or Spanish[3] origin (both attributed to the French word pingouin "auk"), but first appears in English or Dutch.[1]



Some dictionaries suggest a derivation from Welsh pen "head" and gwyn "white", including the Oxford English Dictionary[4], the American Heritage Dictionary[5], the Century Dictionary[6] and Merriam-Webster[7], on the basis that the name was originally applied to the great auk, which had white spots in front of its eyes (although its head was black).



An alternative etymology, found in a few English dictionaries, links the word to Latin pinguis "fat", from its perceived appearance. This etymology would be improbable if "penguin" were found to have been originally applied to the great auk, as some sources suggest.[4][6][2]



A third theory states that the word is an alteration of “pen-wing”, with reference to the rudimentary wings of both great auks and penguins. This has been criticised for the unexplained nature of the alteration of the word.[6]



Systematics and evolution

Living species and recent extinctions



Emperor Penguins (Aptenodytes forsteri), the largest living species.

Adelie Penguin (Pygoscelis adeliae) feeding young. Like its relatives, a neatly bi-coloured species with a head marking.

Magellanic Penguins (Spheniscus magellanicus) guarding nest burrow. The closed neck collar denotes this species.

Closeup of Southern Rockhopper Penguin (Eudyptes chrysocome).The number of extant penguin species is debated. Depending on which authority is followed, penguin biodiversity varies between 17 and 20 living species, all in the subfamily Spheniscinae. Some sources consider the White-flippered Penguin a separate Eudyptula species, while others treat it as a subspecies of the Little Penguin;[8][9] the actual situation seems to be more complicated.[10] Similarly, it is still unclear whether the Royal Penguin is merely a color morph of the Macaroni penguin. The status of the Rockhopper penguins is also unclear.



Updated after Marples (1962), Acosta Hospitaleche (2004), and Ksepka et al. (2006).



Subfamily Spheniscinae – Modern penguins



Aptenodytes – Great penguins

King Penguin, Aptenodytes patagonicus

Emperor Penguin, Aptenodytes forsteri

Pygoscelis – Brush-tailed penguins

Adélie Penguin, Pygoscelis adeliae

Chinstrap Penguin, Pygoscelis antarctica

Gentoo Penguin, Pygoscelis papua

Eudyptula – Little penguins

Little Blue Penguin, Eudyptula minor

Northern Little Penguin, Eudyptula albosignata (provisional)

Spheniscus – Banded penguins

Magellanic Penguin, Spheniscus magellanicus

Humboldt Penguin, Spheniscus humboldti

Galapagos Penguin, Spheniscus mendiculus

African Penguin, Spheniscus demersus

Megadyptes

Yellow-eyed Penguin, Megadyptes antipodes

Waitaha Penguin, Megadyptes waitaha (extinct)

Eudyptes – Crested penguins

Fiordland Penguin, Eudyptes pachyrynchus

Snares Penguin, Eudyptes robustus

Erect-crested Penguin, Eudyptes sclateri

Western Rockhopper Penguin, Eudyptes chrysocome

Eastern Rockhopper Penguin, Eudyptes filholi

Northern Rockhopper Penguin, Eudyptes moseleyi

Royal Penguin, Eudyptes schlegeli (disputed)

Macaroni Penguin, Eudyptes chrysolophus

Chatham Islands Penguin, Eudyptes sp. (extinct)

Fossil genera

Order Sphenisciformes



Basal and unresolved taxa (all fossil)

Waimanu – basal (Middle-Late Paleocene)

Perudyptes (Middle Eocene of Atacama Desert, Peru) – basal?

Spheniscidae gen. et sp. indet. CADIC P 21 (Leticia Middle Eocene of Punta Torcida, Argentina)[11]

Delphinornis (Middle/Late Eocene? – Early Oligocene of Seymour Island, Antarctica) – Palaeeudyptinae, basal, new subfamily 1?

Archaeospheniscus (Middle/Late Eocene – Late Oligocene) – Palaeeudyptinae? New subfamily 2?

Marambiornis (Late Eocene –? Early Oligocene of Seymour Island, Antarctica) – Palaeeudyptinae, basal, new subfamily 1?

Mesetaornis (Late Eocene –? Early Oligocene of Seymour Island, Antarctica) – Palaeeudyptinae, basal, new subfamily 1?

Tonniornis (Late Eocene –? Early Oligocene of Seymour Island, Antarctica)

Wimanornis (Late Eocene –? Early Oligocene of Seymour Island, Antarctica)

Duntroonornis (Late Oligocene of Otago, New Zealand) – possibly Spheniscinae

Korora (Late Oligocene of S Canterbury, New Zealand)

Platydyptes (Late Oligocene of New Zealand) – possibly not monophyletic; Palaeeudyptinae, Paraptenodytinae or new subfamily?

Spheniscidae gen. et sp. indet. (Late Oligocene/Early Miocene of Hakataramea, New Zealand)[verification needed]

Madrynornis (Puerto Madryn Late Miocene of Argentina) – possibly Spheniscinae

Pseudaptenodytes (Late Miocene/Early Pliocene)

Dege (Early Pliocene of South Africa) – possibly Spheniscinae

Marplesornis (Early Pliocene) – possibly Spheniscinae

Nucleornis (Early Pliocene of Duinfontain, South Africa) – possibly Spheniscinae

Inguza (Late Pliocene) – probably Spheniscinae; formerly Spheniscus predemersus



A damaged tarsometatarsus of the prehistoric Narrow-flippered Penguin (Palaeeudyptes antarcticus).Family Spheniscidae

Subfamily Palaeeudyptinae – Giant penguins (fossil)

Crossvallia (Cross Valley Late Paleocene of Seymour Island, Antarctica) – tentatively assigned to this subfamily

Anthropornis (Middle Eocene? – Early Oligocene of Seymour Island, Antarctica) – tentatively assigned to this subfamily

Nordenskjoeld's Giant Penguin, Anthropornis nordenskjoeldi

Icadyptes (Late Eocene of Atacama Desert, Peru)

Palaeeudyptes (Middle/Late Eocene – Late Oligocene) – polyphyletic; some belong in other subfamilies

Pachydyptes (Late Eocene)

Anthropodyptes (Middle Miocene) – tentatively assigned to this subfamily

Subfamily Paraptenodytinae – Stout-footed penguins (fossil)

Arthrodytes (San Julian Late Eocene/Early Oligocene – Patagonia Early Miocene of Patagonia, Argentina)

Paraptenodytes (Early – Late Miocene/Early Pliocene)

Subfamily Palaeospheniscinae – Slender-footed penguins (fossil)

Eretiscus (Patagonia Early Miocene of Patagonia, Argentina)

Palaeospheniscus (Early? – Late Miocene/Early Pliocene) – includes Chubutodyptes

Taxonomy

Some recent sources[12] apply the phylogenetic taxon Spheniscidae to what here is referred to as Spheniscinae. Furthermore, they restrict the phylogenetic taxon Sphenisciformes to flightless taxa, and establish the phylogenetic taxon Pansphenisciformes as equivalent to the Linnean taxon Sphenisciformes,[13] i.e., including any flying basal "proto-penguins" to be discovered eventually. Given that neither the relationships of the penguin subfamilies to each other nor the placement of the penguins in the avian phylogeny is presently resolved, this seems spurious[neutrality is disputed] and in any case is confusing; the established Linnean system is thus followed here.



Evolution

The evolutionary history of penguins is well-researched and represents a showcase of evolutionary biogeography; though as penguin bones of any one species vary much in size and few good specimens are known, the alpha taxonomy of many prehistoric forms still leaves much to be desired. Some seminal articles about penguin prehistory have been published since 2005,[14][15][16][17] the evolution of the living genera can be considered resolved by now.



The basal penguins lived around the time of the Cretaceous–Tertiary extinction event somewhere in the general area of (southern) New Zealand and Byrd Land, Antarctica.[16] Due to plate tectonics, these areas were at that time less than 1,500 kilometers (932 mi) apart rather than the 4,000 kilometers (2,485 mi) of today. The most recent common ancestor of penguins and their sister clade can be roughly dated to the Campanian–Maastrichtian boundary, around 70–68 mya.[15][17][18] What can be said as certainly as possible in the absence of direct (i.e., fossil) evidence is that by the end of the Cretaceous, the penguin lineage must have been evolutionarily well distinct, though much less so morphologically; it is fairly likely that they were not yet entirely flightless at that time, as flightless birds have generally low resilience to the breakdown of trophic webs that follows the initial phase of mass extinctions because of their below-average dispersal capabilities (see also Flightless Cormorant).[citation needed]



The basal fossils

The oldest known fossil penguin species is Waimanu manneringi, which lived in the early Paleocene epoch of New Zealand, or about 62 mya.[17] While they were not as well-adapted to aquatic life as modern penguins, Waimanu were generally loon-like birds but already flightless, with short wings adapted for deep diving.[citation needed] They swam on the surface using mainly their feet, but the wings were – as opposed to most other diving birds, living and extinct – already adapting to underwater locomotion.[citation needed]



Perudyptes from northern Peru was dated to 42 mya. An unnamed fossil from Argentina proves that by the Bartonian (Middle Eocene), some 39–38 mya,[19] primitive penguins had spread to South America and were in the process of expanding into Atlantic waters.[13]



Palaeeudyptines

During the Late Eocene and the Early Oligocene (40–30 mya), some lineages of gigantic penguins existed. Nordenskjoeld's Giant Penguin was the tallest, growing nearly 1.80 meters (6 ft) tall. The New Zealand Giant Penguin was probably the heaviest, weighing 80 kg or more. Both were found on New Zealand, the former also in the Antarctic farther eastwards.



Traditionally, most extinct species of penguins, giant or small, had been placed in the paraphyletic subfamily called Palaeeudyptinae. More recently, with new taxa being discovered and placed in the phylogeny if possible, it is becoming accepted that there were at least two major extinct lineages. One or two closely related ones occurred in Patagonia, and at least one other—which is or includes the paleeudyptines as recognized today – occurred on most Antarctic and subantarctic coasts.



But size plasticity seems to have been great at this initial stage of penguin radiation: on Seymour Island, Antarctica, for example, around 10 known species of penguins ranging in size from medium to huge apparently coexisted some 35 mya during the Priabonian (Late Eocene).[20] It is not even known whether the gigantic palaeeudyptines constitute a monophyletic lineage, or whether gigantism was evolved independently in a much restricted Palaeeudyptinae and the Anthropornithinae – whether they were considered valid, or whether there was a wide size range present in the Palaeeudyptinae as delimited as usually done these days (i.e., including Anthropornis nordenskjoeldi).[16] The oldest well-described giant penguin, the 5-foot-tall Icadyptes salasi, actually occurred as far north as northern Peru about 36 mya.



In any case, the gigantic penguins had disappeared by the end of the Paleogene, around 25 mya. Their decline and disappearance coincided with the spread of the Squalodontoidea and other primitive, fish-eating toothed whales, which certainly competed with them for food, and were ultimately more successful.[15] A new lineage, the Paraptenodytes, which includes smaller but decidedly stout-legged forms, had already arisen in southernmost South America by that time. The early Neogene saw the emergence of yet another morphotype in the same area, the similarly-sized but more gracile Palaeospheniscinae, as well as the radiation that gave rise to the penguin biodiversity of our time.



Origin and systematics of modern penguins

Modern penguins consititute two undisputed clades and another two more basal genera with more ambiguous relationships.[14] 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.[15] Presumedly diverging from other penguins around 40 mya,[15] 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. Also, the earliest spheniscine lineages are those with the most southern distribution.



The genus Aptenodytes appears to be the basalmost divergence among living penguins [21] [22] they have bright yellow-orange neck, breast, and bill patches; incubate by placing their eggs on their feet, and when they hatch the chicks are almost naked. This genus has a distribution centered on the Antarctic coasts and barely extends to some subantarctic islands today.



Pygoscelis contains species with a fairly simple black-and-white head pattern; their distribution is intermediate, centered 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,[23] 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.[15]



The genera Spheniscus and Eudyptula contain species with a mostly subantarctic distribution centered on South America; some, however, range quite far northwards. They all lack carotenoid coloration, 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.[15] While the two genera separated during this time, the present-day diversity is the result of a Pliocene radiation, taking place some 4–2 mya.[15]



The Megadyptes–Eudyptes clade occurs at similar latitudes (though not as far north as the Galapagos Penguin), has its highest diversity in the New Zealand region, and represent a westward dispersal. They are characterized by hairy yellow ornamental head feathers; their bills are at least partly red. These two genera diverged apparently in the Middle Miocene (Langhian, roughly 15–14 mya), but again, the living species of Eudyptes are the product of a later radiation, stretching from about the late Tortonian (Late Miocene, 8 mya) to the end of the Pliocene.[15]



The geographical and temporal pattern or spheniscine evolution corresponds closely to two episodes of global cooling documented in the paleoclimatic record.[15] 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. With habitat on the Antarctic coasts declining, by the Priabonian more hospitable conditions for most penguins existed in the subantarctic regions rather than in Antarctica itself[24]. Notably, the cold Antarctic Circumpolar Current also started as a continuous circumpolar flow only around 30 mya, on the one hand forcing the Antarctic cooling, and on the other facilitating the eastward expansion of Spheniscus to South America and eventually beyond.[15] Despite this, there is no fossil evidence to support the idea a crown radiation from the antarctic continent in the Paleogene [25].



Later, an interspersed period of slight warming was ended by the Middle Miocene Climate Transition, a sharp drop in global average temperature from 14–12 mya, and similar abrupt cooling events followed at 8 mya and 4 mya; by the end of the Tortonian, the Antarctic ice sheet was already much like today in volume and extent. The emergence of most of today's subantarctic penguin species almost certainly was caused by this sequence of Neogene climate shifts