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Penguin

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Penguins
Temporal range: Paleocene-Recent
Chinstrap Penguin, Pygoscelis antarctica
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Aves
Order: Sphenisciformes
Sharpe, 1891
Family: Spheniscidae
Bonaparte, 1831
Modern genera
Some penguins are curious.

Penguins (order Sphenisciformes, family Spheniscidae) are an order of aquatic, flightless birds living almost exclusively in the Southern Hemisphere.

The number of penguin species has been and still is a matter of debate. Depending on which authority is followed, biodiversity varies between 16 and 19 living species. Some sources consider the White-flippered Penguin a separate Eudyptula species, while others treat it as a subspecies of the Little Penguin (e.g. Williams, 1995; Davis & Renner, 2003); the actual situation seems to be more complicated (Banks et al. 2002). Similarly, it is still unclear whether the Royal Penguin is merely a color morph of the Macaroni penguin. Also possibly eligible to be treated as a separate species is the Northern population of Rockhopper penguins (Davis & Renner, 2003). 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 Galápagos Islands (the Galápagos Penguin).

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). Generally larger penguins retain heat better, and thus inhabit colder regions, while smaller penguins are found in temperate or even tropical climates (see also Bergmann's Rule). Some prehistoric species attained enormous sizes, becoming as high as an adult human; see below for more.

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.

Penguins seem to have no fear of humans and have approached groups of explorers without hesitation. This is probably on account of there being no land predators in Antarctica or the nearby offshore islands that prey on or attack penguins. Instead, penguins are at risk at sea from predators such as the leopard seal.

Anatomy

Penguins are superbly adapted to an aquatic life. Their wings have become flippers, useless for flight in the air. In the water, however, penguins are astonishingly agile. Within the smooth plumage a layer of air is preserved, ensuring buoyancy. The air layer also helps insulate the birds in cold waters. On land, penguins use their tails and wings to maintain balance for their upright stance.

All penguins are countershaded - that is, they have a white underside and a dark (mostly black) upperside. This is for camouflage. A predator looking up from below (such as an orca or a leopard seal) has difficulty distinguishing between a white penguin belly and the reflective water surface. The dark plumage on their backs camouflages them from above.

Diving penguins reach 6 to 12 km/h (3.7 to 7.5 mph), though there are reports of velocities of 27 km/h (17 mph) (which are more realistic in the case of startled flight). The small penguins do not usually dive deep; they catch their prey near the surface in dives that normally last only one or two minutes. Larger penguins can dive deep in case of need. Dives of the large Emperor Penguin have been recorded which reach a depth of 565 m (1870 ft) and last up to 20 minutes.

Penguins either waddle on their feet or slide on their bellies across the snow, a movement called "tobogganing", which allows them to conserve energy and move relatively fast at the same time.

Penguins have an excellent sense of hearing. Their eyes are adapted for underwater vision, and are their primary means of locating prey and avoiding predators; in air, conversely, they are nearsighted. Their sense of smell has not been researched so far.

They are able to drink salt water safely because their supraorbital gland filters excess salt from the bloodstream. The salt is excreted in a concentrated fluid from the nasal passages.

Mating habits

Some penguins mate for life, others for just one season. They generally raise a small brood, and the parents cooperate in caring for the clutch and for the young. During the cold season on the other hand the mates separate for several months to protect the egg. The male stays with the egg and keeps it warm, and the female goes out to sea and finds food so that when it comes home, the baby will have food to eat. Once the female comes back, they switch. When mothers lose a chick, they sometimes attempt to "steal" another mother's chick, usually unsuccessfully as other females in the vicinity assist the defending mother in keeping her chick. As the young grow, they assemble in large groups called crèches in some species, such as Emperor Penguins.

Homosexual Behaviour

In early February 2004 the New York Times reported a male pair of Chinstrap penguins in the Central Park Zoo in New York City were partnered, and when given an egg which needed incubation, successfully hatched it. Other penguins in New York have also been reported to be forming same-sex pairs.

This was the basis for the children's picture book And Tango Makes Three. The couple about whom the book was based, Roy and Silo, would see further interesting developments in their relationship when in September 2005, Silo left Roy for a female penguin.

Zoos in Japan and Germany have also documented male penguin couples. The couples have been shown to build nests together and use a stone to replace an egg in the nest. Researchers at Rikkyo University in Tokyo found twenty such pairs at sixteen major aquariums and zoos in Japan. Bremerhaven Zoo in Germany attempted to break up the male couples by importing female penguins from Sweden and separating the male couples; they were unsuccessful. The zoo director stated the relationships were too strong between the older couples.

Systematics and evolution

Systematics

Updated after Marples, 1962, and Acosta Hospitaleche, 2004 . See the gallery for images of most living species.

ORDER SPHENISCIFORMES

  • Basal and unresolved taxa
    • Waimanu - basal (Middle-Late Eocene)
    • Sphenisciformes gen. et sp. indet. CADIC P 21 (Leticia Middle Eocene of Punta Torcida, Argentina: Clarke et al. 2003)
  • Family Spheniscidae

Evolution

The evolutionary history of penguins is by now fairly 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. A number of seminal articles dealing with penguin prehistory has been published in 2006, and at least the evolution of the living genera can be considered resolved by now. According to the comprehensive review of the available evidence by Ksepka et al. (2006), the basal penguins lived around the time of the Cretaceous-Paleogene extinction event somewhere in the general area of (southern) New Zealand and Byrd Land, Antarctica. Due to plate tectonics, these areas were at that time less than 1500 kilometers apart rather than the 4000 km of today.

The oldest known fossil penguin species are the Waimanu, which lived in the early Paleocene epoch of New Zealand, or about 62 mya. 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. 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.

An unnamed fossil from Argentina proves that by the Bartonian (Middle Eocene), some 39-38 mya, primitive penguins had spread to South America and were in the process of expanding into Atlantic waters (Clarke et al. 2003).

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 feet) 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.

"Palaeeudyptines"
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 2 major extinct lineages. One or two closely related ones occurred in Patagonia, and at least one other - which is or includes the paleeeudyptines as recognized today -, which 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 ten known species of penguins ranging from medium to huge size apparently coexisted during the Late Eocene, some 35 mya (Jadwiszczak 2006). 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 - then valid - Anthropornithinae, or whether there was a wide size range present in the Palaeeudyptinae which would then be delimited as usually done these days (i.e., including Anthropornis) (Ksepka et al. 2006).

In any case, the gigantic penguins had disappeared by the end of the Paleogene, around 25 mya. A new lineage, the Paraptenodytinae 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 beginning of the radiation which gave rise to the penguin biodiversity of our time.

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.

Name

Penguin is thought by some to derive from the Welsh words pen (head) and gwyn (white), applied to the Great Auk, which had a conspicuous white patch between the bill and the eye (although its head was black), or from an island off Newfoundland known as "White Head" due to a large white rock. This may be, however, a false etymology created by Dr. John Dee in his book on Prince Madoc of Wales, supposedly one of the discoverers of America. By this Dee hoped to cement Queen Elizabeth I's claim, as a Tudor, to the New World. Penguins live nowhere near Newfoundland, nor do they generally have white heads, but they do look remarkably like Great Auks in general shape.

According to another theory, the original name was pen-wing, with reference to the rudimentary wings of both Great Auks and penguins. A third theory is that penguin comes from the Latin pinguis (fat). This has added credibility because in two other Germanic languages, Dutch 'pinguïn' and German, 'Pinguin' both have the 'i' vowel too. While it has been replaced by an 'e' in the English spelling, it can still be heard. By simply looking at the word's pronunciation and comparing that to the Dutch and German words, one could assume a common Latin root - after the first Germanic sound shift (500-200 BC) that makes a PIE 'p' into a 'f'. However, a Welsh 'i' is often sound-shifted to an 'e' in the English language, so a Welsh origin cannot be dismissed.

Penguins in popular culture

Tux the Linux mascot
Main article: Penguins in popular culture

Penguins are popular around the world, primarily for their unusually upright, waddling pace and (compared to other birds) lack of fear of humans. Their striking black and white plumage is often likened to a tuxedo suit and generates humorous remarks about the bird being "well dressed". Perhaps in reaction to this cutesy stereotype, fictional penguins are occasionally presented as grouchy or even sinister. Penguins have also been the subject of many books and documentary films.

Gallery of living species

References

  • Acosta Hospitaleche, Carolina (2004): Los pingüinos (Aves, Sphenisciformes) fósiles de Patagonia. Sistemática, biogeografía y evolución. Doctoral thesis, Department of Natural Sciences and Museum, Universidad Nacional de La Plata. La Plata, Argentina. PDF fulltext
  • Banks, Jonathan C.; Mitchell, Anthony D.; Waas, Joseph R. & Paterson, Adrian M. (2002): An unexpected pattern of molecular divergence within the blue penguin (Eudyptula minor) complex. Notornis 49(1): 29–38. PDF fulltext
  • Clarke, Julia A.; Olivero, Eduardo B. & Puerta, Pablo (2003): Description of the earliest fossil penguin from South America and first Paleogene vertebrate locality of Tierra Del Fuego, Argentina. American Museum novitates 3423: 1-18. PDF fulltext
  • Davis; Lloyd S. & Renner; M. (1995). Penguins . London: T & A D Poyser. ISBN 0-7136-6550-5
  • Jadwiszczak, Piotr (2006): Eocene penguins of Seymour Island, Antarctica: taxonomy. Polish Polar Research 27(1), 3–62. PDF fulltext
  • Ksepka, Daniel T., Bertelli, Sara & Giannini, Norberto P. (2006): The phylogeny of the living and fossil Sphenisciformes (penguins). Cladistics 22(5): 412–441. doi:10.1111/j.1096-0031.2006.00116.x (HTML abstract)
  • Marples, B. J. (1962): Observations on the history of penguins. In: Leeper, G. W. (ed.), The evolution of living organisms. Melbourne, Melbourne University Press: 408-416.
  • Mayr, G. (2005): Tertiary plotopterids (Aves, Plotopteridae) and a novel hypothesis on the phylogenetic relationships of penguins (Spheniscidae). Journal of Zoological Systematics and Evolutionary Research 43(1): 61-71. doi:10.1111/j.1439-0469.2004.00291.x PDF fulltext
  • Williams; Tony D. (1995). The Penguins - Spheniscidae . Oxford: Oxford University Press. ISBN 0-19-854667-X

Footnotes

  1. "Animal Fact Sheets". Retrieved 2006-07-21.
  2. "Humboldt Penguin :: Saint Louis Zoo". Retrieved 2006-07-21.
  3. "African Penguins and Penguins of the World". Retrieved 2006-07-21.
  4. "Columbia News Service: June 10, 2002: They're in love. They're gay. They're penguins... And they're not alone". Retrieved 2006-07-21.
  5. "365gay.com: Gay Penguins Resist 'Aversion Therapy'". Retrieved 2006-07-21.
  6. Probably, the last common ancestor of penguins and their sister clade lived some time earlier. 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 habe been evolutionarily well distinct, though much less so morphologically.

External links

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