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?Whale
North Atlantic right whales, mother and calf
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Subclass: Eutheria
Order: Cetacea

Whale (origin Old English hƿæl) is the common name for various marine mammals of the order Cetacea.[1] The term whale sometimes refers to all cetaceans, but more often it excludes dolphins and porpoises,[2] which belong to suborder Odontoceti (toothed whales). This suborder also includes the sperm whale, killer whale, pilot whale, and beluga whale. The other Cetacean suborder Mysticeti (baleen whales) are filter feeders that eat small organisms caught by straining seawater through a comblike structure found in the mouth called baleen. This suborder includes the blue whale, the humpback whale, the bowhead whale and the minke whale. All Cetacea have forelimbs modified as fins, a tail with horizontal flukes, and nasal openings (blowholes) on top of the head.

Whales range in size from the blue whale, the largest animal known to have ever existed[3] at Template:Convert/LoffAonDbSoffTemplate:Convert/test/Aon and Template:Convert/tTemplate:Convert/test/A, to various pygmy species, such as the pygmy sperm whale at Template:Convert/LoffAonDbSoffTemplate:Convert/test/Aon.

Whales collectively inhabit all the world's oceans and number in the millions, with annual population growth rate estimates for various species ranging from 3% to 13%.[4] For centuries, whales have been hunted for meat and as a source of raw materials. By the middle of the 20th century, however, industrial whaling had left many species seriously endangered, leading to the end of whaling in all but a few countries.

Taxonomy

Cetaceans are divided into two suborders:

  • The largest suborder, Mysticeti (baleen whales) are characterized by baleen, a sieve-like structure in the upper jaw made of keratin, which it uses to filter plankton from the water.
  • Odontoceti (toothed whales) bear sharp teeth for hunting. Odontoceti also include dolphins and porpoises.

Both cetaceans and artiodactyl are now classified under the super-order Cetartiodactyla which includes both whales and hippopotamuses. Whales are the hippopotamus's closest living relatives.[5]

Evolution

File:Ambulocetus BW.jpg

All cetaceans, including whales, dolphins and porpoises, are descendants of land-living mammals of the Artiodactyl order (even-toed ungulates). Both are related to the Indohyus (an extinct semi-aquatic deer-like ungulate) from which they split around 54 million years ago.[6][7] Primitive whales probably first took to the sea about 50 million years ago and became fully aquatic about 5–10 million years later.[8]

Anatomy

Like all mammals, whales breathe air, are warm-blooded, nurse their young with milk from mammary glands, and have body hair.[citation needed]

Beneath the skin lies a layer of fat called blubber, which stores energy and insulates the body. Whales have a spinal column, a vestigial pelvic bone, and a four-chambered heart. The neck vertebrae are typically fused, trading flexibility for stability during swimming.[citation needed]

Blowhole(s)

File:Baleen parts.png

Whales breathe via blowholes; baleen whales have two and toothed whales have one. These are located on the top of the head, allowing the animal to remain mostly submerged whilst breathing. Breathing involves expelling excess water from the blowhole, forming an upward spout, followed by inhaling air into the lungs. Spout shapes differ among species and can help with identification.

Appendages

The body shape is fusiform and the modified forelimbs, or fins, are paddle-shaped. The end of the tail is composed of two flukes, which propel the animal by vertical movement, as opposed to the horizontal movement of a fish tail. Although whales do not possess fully developed hind limbs, some (such as sperm whales and baleen whales) possess discrete rudimentary appendages, which may even have feet and digits. Most species have a dorsal fin.[citation needed]

Dentition

Toothed whales, such as the sperm whale, possess teeth with cementum cells overlying dentine cells. Unlike human teeth, which are composed mostly of enamel on the portion of the tooth outside of the gum, whale teeth have cementum outside the gum. Only in larger whales, where the cementum has been worn away on the tip of the tooth, does enamel show.[9]

Instead of teeth, Baleen whales have a row of plates on the upper side of their jaws that resemble the "teeth" of a comb.

Ears

The whale ear has specific adaptations to the marine environment. In humans, the middle ear works as an impedance matcher between the outside air’s low impedance and the cochlear fluid’s high impedance. In aquatic mammals such as whales, however, there is no great difference between the outer and inner environments. Instead of sound passing through the outer ear to the middle ear, whales receive sound through the throat, from which it passes through a low-impedance fat-filled cavity to the inner ear.[10] The whale ear is acoustically isolated from the skull by air-filled sinus pockets, which allow for greater directional hearing underwater. [11]

Life history/behavior

Reproduction

Males are called 'bulls', females, 'cows' and newborns, 'calves'. Most species do not maintain fixed partnerships and females have several mates each season.[12][13]

The female delivers usually a single calf tail-first to minimize the risk of drowning. Whale cows nurse by actively squirting milk, so fatty that it has the consistency of toothpaste, into the mouths of their young.[12] Nursing continues for more than a year in many species, and is associated with a strong bond between mother and calf. Reproductive maturity occurs typically at seven to ten years. This mode of reproduction produces few offspring, but increases survival probability.

Socialization

Whales are known to teach, learn, cooperate, scheme, and even grieve.[14] The neocortex of many species of whale is home to elongated spindle neurons that, prior to 2007, were known only in hominids.[15] In humans these cells are involved in social conduct, emotions, judgment, and theory of mind.[16] Whale spindle neurons are found in areas of the brain homologous to where they are found in humans, suggesting that they perform a similar function. [17]

Sleep

File:Humpback stellwagen edit.jpg

Unlike most animals, whales are conscious breathers. All mammals sleep, but whales cannot afford to become unconscious for long because they may drown. It is thought that only one hemisphere of the whale's brain sleeps at a time, so they rest but are never completely asleep.[18]

Surfacing behavior

Main article: Whale surfacing behavior

Many whales exhibit behaviors such as breaching and tail slapping that expose large parts of their bodies to the air.

Lifespan

Whale lifespans vary among species and are not well characterized. Whaling left few older individuals to observe directly. R.M. Nowak of Johns Hopkins University estimated that humpback whales may live as long as 77 years.[19] In 2007, a 19th century lance fragment was found in a bowhead whale off Alaska, suggesting the individual could be between 115 and 130 years old.[20] Aspartic acid racemization in the whale eye, combined with a harpoon fragment, indicated an age of 211 years for another male, which, if true would make bowheads the longest-lived extant mammal species.[21][22] The accuracy of this technique has been questioned because racemization did not correlate well with other dating methods.[23]

Vocalization

Some species, such as the humpback whale, communicate using melodic sounds, known as whale song. These sounds can be extremely loud, depending on the species. Sperm whales have only been heard making clicks, while toothed whales (Odontoceti) use echolocation that can generate about 20,000 watts of sound (+73 dBm or +43 dBw[24]) and be heard for many miles. Whale vocalization is likely to serve many purposes, including echolocation, mating, and identification.[citation needed]

Ecology

Feeding

Whales are generally classed as predators, but their food ranges from microscopic plankton to very large animals.

Toothed whales eat fish and squid which they hunt by use of echolocation. Orcas sometimes eat other marine mammals, including whales.

Baleen whales such as humpbacks and blues feed only in arctic waters, eating mostly krill. They imbibe enormous amounts of seawater which they expel through their baleen plates. The water is then expelled and the krill is retained on the plates and then swallowed.[12] Whales do not drink seawater but indirectly extract water from their food by metabolizing fat.[12]


Naval sonar

Environmentalists speculate that advanced naval sonar endangers some cetaceans, including whales. In 2003 British and Spanish scientists suggested in Nature that the effects of sonar trigger whale beachings and to signs that such whales have experienced decompression sickness.[25] Responses in Nature the following year discounted the explanation.[26]

Mass beachings occur in many species, mostly beaked whales that use echolocation for deep diving. The frequency and size of beachings around the world, recorded over the last 1,000 years in religious tracts and more recently in scientific surveys, have been used to estimate the population of various whale species by assuming that the proportion of the total whale population beaching in any one year is constant. Beached whales can give other clues about population conditions, especially health problems. For example, bleeding around ears, internal lesions, and nitrogen bubbles in organ tissue suggest decompression sickness.[14]

Following public concern, the U.S. Defense department was ordered by the 9th Circuit Court to strictly limit use of its Low Frequency Active Sonar during peacetime. Attempts by the UK-based Whale and Dolphin Conservation Society to obtain a public inquiry into the possible dangers of the Royal Navy's equivalent (the "2087" sonar launched in December 2004) failed as of 2008. The European Parliament has requested that EU members refrain from using the powerful sonar system until an environmental impact study has been carried out.


In mythology

File:Nantucket historical assocation whaling museum weather vane.jpg

Whales were little understood for most of human history as they spend up to 90% of the lives underwater, only surfacing briefly to breathe.[27] They also include the largest animals on the planet, so it is not surprising that many cultures, even those that have hunted them, hold them in awe and feature them in their mythologies.

In China, Yu-kiang, a whale with the hands and feet of a man was said to rule the ocean.[28]

In the Tyrol region of Austria it was said that if a sunbeam were to fall on a maiden entering womanhood, she would be carried away in the belly of a whale.[28]

Paikea, the youngest and favourite son of the chief Uenuku from the island of Mangaia in the present day Cook Islands in New Zealand was said by the Kati Kuri people of Kaikoura to have come from the Pacific Islands on the back of a whale many centuries before.[29] The novel and movie Whale Rider follow the trials of a girl named Paikia, who lives in such a culture.

The whale features in Inuit creation myths. When ‘Big Raven', a deity in human form, found a stranded whale, he was told by the Great Spirit where to find special mushrooms that would give him the strength to drag the whale back to the sea and thus return order to the world.[30]

The Tlingit people of northern Canada said that the Orcas were created when the hunter Natsihlane carved eight fish from yellow cedar, sang his most powerful spirit song and commanded the fish to leap into the water.[30]

In Icelandic legend a man threw a stone at a fin whale and hit the blowhole, causing the whale to burst. The man was told not to go to sea for twenty years but in the nineteenth year he went fishing and a whale came and killed him.[30]

In East African legend King Sulemani asked God that He might permit him to feed all the beings on earth. A whale came and ate until there was no corn left and then told Sulemani that he was still hungry and that there were 70,000 more in his tribe. Sulemani then prayed to God for forgiveness and thanked the creature for teaching him a lesson in humility.[30]

Some cultures associate divinity with whales, such as among Ghanaians and Vietnamese, who occasionally hold funerals for beached whales, a throwback to Vietnam's ancient sea-based Austro-asiatic culture.[31][32][33][34] The whale is a revered creature to Vietnamese fishermen. They are respectfully addressed as "Lord". If one finds a stranded whale corpse, one is in charge of holding the funeral for the "Lord" as if it was one's own parent.

The story of Jonah being swallowed by a whale also is told in the Qur'an.[35]

Whales in the Bible

The Bible, 1611 Authorized Version, expressly mentions whales four times:

  • Genesis 1:21 And God created great whales, and every living creature that moveth, which the waters brought forth abundantly, after their kind, and every winged fowl after his kind: and God saw that it was good.
  • Job 7:12 Am I a sea, or a whale, that thou settest a watch over me?
  • Ezekiel 32:2 Son of man, take up a lamentation for Pharaoh king of Egypt, and say unto him, Thou art like a young lion of the nations, and thou art as a whale in the seas: and thou camest forth with thy rivers, and troubledst the waters with thy feet, and fouledst their rivers.
  • Matthew 12:40 For as Jonas was three days and three nights in the whale’s belly; so shall the Son of man be three days and three nights in the heart of the earth.

The translators in that latter verse above thereby identified the "great fish" of the book of Jonah as a whale. It is apparent that Jeremiah recognized that some great fish are mammals. The English word "monster", (used in the ordinary sense of a "huge animal",) is used in the Bible in Jeremiah's Lamentations to refer to whales:

  • Lamentations 4:3 Even the sea monsters draw out the breast, they give suck to their young ones: the daughter of my people is become cruel, like the ostriches in the wilderness.


See also


References

  1. (2007) Brown, Lesley Shorter Oxford English Dictionary, Sixth, Oxford: Oxford University press.
  2. ACS – American Cetacean Society. Acsonline.org. Retrieved on 2011-11-18.
  3. What is the biggest animal ever to exist on Earth?. How Stuff Works. URL accessed on 2007-05-29.
  4. Whale Population Estimates. International Whaling Commission. URL accessed on March 2010.
  5. Anon Scientists find missing link between the whale and its closest relative, the hippo. PhysOrg.com. PhysOrg.com. URL accessed on 6 May 2010.
  6. Northeastern Ohio Universities Colleges of Medicine and Pharmacy. Whales Descended From Tiny Deer-like Ancestors. ScienceDaily. URL accessed on 2007-12-21.
  7. Dawkins, Richard (2004). The Ancestor's Tale, Boston: Houghton Mifflin Company.
  8. includeonly>"How whales learned to swim", BBC News, 2002-05-08. Retrieved on 2006-08-20.
  9. "Common Characteristics of Whale Teeth" here [1]
  10. How is that whale listening?. URL accessed on February 4, 2008.
  11. Nummela, Sirpa. (2007). Sound transmission in archaic and modern whales: Anatomical adaptations for underwater hearing.. The Anatomical Record 290 (6): 716–733.
  12. 12.0 12.1 12.2 12.3 Blue Whale.
  13. "Milk". Modern Marvels. The History Channel. 2008-01-07.
  14. 14.0 14.1 includeonly>Siebert, Charles. "Watching Whales Watching Us", New York Times Magazine, July 8, 2009.
  15. cite journal |author=Watson, K.K. | title=Dendritic architecture of the Von Economo neurons | journal= Neuroscience | volume= 141 |issue=3 |pages= 1107–1112 |year=2006 |doi=10.1016/j.neuroscience.2006.04.084 |last2=Jones |first2=T.K. |last3=Allman |first3=J.M.}}
  16. Allman, John M. (2005). Intuition and autism: a possible role for Von Economo neurons. Trends Cogn Sci 9 (8): 367–373.
  17. Hof, Patrick R. (2007). Structure of the cerebral cortex of the humpback whale, Megaptera novaeangliae (Cetacea, Mysticeti, Balaenopteridae). The Anatomical Record 290 (1): 1–31.
  18. Anon Do whales and dolphins sleep?. How Stuff Works. Discovery Communications. URL accessed on 14 February 2010.
  19. Anon (2005). Humpback Whale. Animal Infor. Animal Info. URL accessed on 25 February 2010.
  20. includeonly>Conroy, Erin. "Netted whale hit by lance a century ago", June, 2007. Retrieved on 2009-10-05.
  21. Bowhead Whales May Be the World's Oldest Mammals. URL accessed on 2008-03-25.
  22. George, J.C. (1999). Age and growth estimates of bowhead whales (Balaena mysticetus) via aspartic acid racemization. Can. J. Zool. 77 (4): 571–580.
  23. Brignole, Edward, McDowell, Julie Amino Acid Racemization. Today's chemist at work. American Chemical Society. URL accessed on 25 February 2010.
  24. dBm – dBw Watts conversion chart, Radio-Electronics.com
  25. includeonly>"Sonar may cause Whale deaths", BBC News, 2003-10-08. Retrieved on 2006-09-14.
  26. Piantadosi CA, Thalmann ED (2004-04-15). Pathology: whales, sonar and decompression sickness. Nature 428 (6894): 716–718.
  27. Bird, Jonathon Sperm Wales:The deep rivers of the ocena. The Wonders of the Seas. jonathon.bird.org. URL accessed on 14 February 2010.
  28. 28.0 28.1 Jones, Adair In search of . . . whales in literature. Wordpress.com. wordpress. URL accessed on 14 February 2010.
  29. Anon Whales. Tinirau education resource. URL accessed on 14 February 2010.
  30. 30.0 30.1 30.2 30.3 Anon Whale Mythology from around the World. The Creative Continuum. worldtrans.org. URL accessed on 14 February 2010.
  31. Whale funeral draws 1000 mourners in Vietnam. AFP. Sydney Morning Herald. URL accessed on 15 April 2011.
  32. includeonly>"Thousand gather for whale's funeral in Vietnam", The Independent. Retrieved on 15 April 2011.
  33. Viegas, Jennifer Thousands Mourn Dead Whale in Vietnam. Discovery News. URL accessed on 15 April 2011.
  34. Funeral for a Whale held at Apam. Ghana News Agency. GhanaWeb. URL accessed on 15 April 2011.
  35. Qutb, Sayyid Jonah and the Whale. Arab news. Arab News. URL accessed on 14 February 2010.

Further reading

  • Carwardine, M. (2000). Whales, Dolphins and Porpoises, Dorling Kindersley..
  • Williams, Heathcote (1988). Whale Nation, New York: Harmony Books..

External links

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