Whale
| Whale An informal group within the infraorder Cetacea | |
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| Southern right whale | |
Scientific classification
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| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Mammalia |
| Order: | Artiodactyla |
| Suborder: | Whippomorpha |
| Infraorder: | Cetacea |
| Groups included | |
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| Cladisticallyincluded but traditionally excluded taxa | |
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Whalesare a group ofcetaceanmammalsthat live in the ocean. Like other mammals, they breatheoxygenfrom theair,have a small amount ofhair,and arewarm blooded.
There are two basic kinds of whales, and about 100species.[1]
People use the wordwhalein different ways. Some use it for allCetaceansincludingdolphinsandporpoises.These people say that dolphins and porpoises are also whales, because they are also Cetaceans. Others separate out the dolphins and porpoises: common English-speaking people have never called them or thought of them as whales unless they are very large. Actually, there is no clear line between whales and dolphins.
Whales have been killed for meat and oil bywhalers.However, many countries havelawssaying not tokill whalesanymore. Some countries, such asIcelandandJapan,do not have these laws. In other countries, such as theUSA,onlyEskimosand someAmerican Indiansmay legally kill whales such as theblue whaleandbeluga whale.
Diet
[change|change source]Baleen whaleseatplanktonandkrill.Plankton are clouds of very small fish floating in the water. The whales' mouths are very large. They open their mouths very wide and hold a big mouthful of sea water. Their throats stretch very wide to make the space inside their mouth even bigger. Then they close their mouth and squeeze out the seawater. The food does not escape because, instead ofteeth,these whales have filters calledbaleen.Baleen is long, hard strips that act like a strainer. The water goes through the baleen. Animals and plants in the water are trapped and swallowed, while the water goes back out.[2]This is very different from the way that toothed whales eat.
Toothed whaleseat larger fish or meat and are like big dolphins. They have sharp teeth and usually have a big forehead. Inside the big forehead is a chamber to make and direct sounds. They make all kinds of sounds, including sounds so loud they can shock fish. They can useecholocationto locate things that they can not see. Some toothed whales, such as thesperm whale,are almost never called dolphins. Some of them are always called dolphins. Others are like dolphins in some ways and like whales in others.
Taxonomy
[change|change source]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 ofkeratin,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 andartiodactylare now classified under the super-orderCetartiodactyla,which includes both whales andhippopotamuses.Whales are the hippopotamus's closest living relatives.[3]
Evolution
[change|change source]All cetaceans, including whales, dolphins and porpoises, are descendants of land-living mammals of theArtiodactylorder(even-toedungulates). Both are related toIndohyus(an extinctsemi-aquaticdeer-like ungulate) from which they split around 54 million years ago.[4][5] Primitive whales probably first took to the sea about 50 million years ago and became fully aquatic about 5-10 million years later.[6]Pakicetusis an importanttransitional species.
Scientists from the University of Plymouth studied many animals that dive and hold their breath, from insects to whales, and they found that larger animals can hold their breath longer than smaller animals because they can store more oxygen for their size, and this difference was much bigger for warm-blooded animals than for cold-blooded animals. They said this may be why modern whales and extinct diving animals likeplesiosaursbecame so large.[7][8]
Physiology
[change|change source]Because of where they live (and unlike many animals), whales are conscious breathers: they decide when to breathe. Whales breathe through blowholes. Baleen whales have two and toothed whales have one. These are on the top of the head: the animal breathes while most of their body is underwater. Breathing first shoots out extra water from the blowhole, making a jet into the air, followed by inhaling air into the lungs.
All mammals sleep, including whales, but they cannot stay in anunconsciousstate for too long, because they need to be conscious to breathe. It is thought that only one hemisphere (half) of their brains sleeps at a time, so that whales are never completely asleep, but still get the rest they need.[9]Whales are thought to sleep around eight hours a day.
A baby whale is called a "calf". One calf is born every two or three years.Gestationtakes up to a year. Nursing continues for more than a year in many species; there is a strong bond between mother and calf. Reproductive maturity occurs at seven to ten years. This mode of reproduction produces few offspring, but increases their chance of surviving. The effect of hunting is severe on these animals, who replace their numbers slowly.[10]
Whale behavior
[change|change source]Socialization
[change|change source]Whales are known to teach, learn, cooperate, scheme, and even grieve.[11]
Breaching
[change|change source]Breachingis what happens when a whale jumps into the air and then purposefully flops down on the water with a great splash. Sometimes it twirls in the air when it does this.Scientistsare not sure whether breaching is done to play, to clean the whale's skin of things that are stuck to it, or to tell other whales something.[12]
There are a number of other behaviors on the surface which are not well understood.[13]'Logging' is when a whale swims slowly at the surface of the ocean with very little movement. When a whale does this, it looks like alogin the water. Some scientists think this is a kind of rest or sleep for whales. 'Spyhopping' is when a whale sits straight up in the water with its head straight up and out of the water. It will sometimes turn around in circles as it spyhops. Some scientists think this might be because whales are trying to see what is happening above water. 'Lobtailing' is done when a whale faces downward in the water. It then slaps the water with athunderoussound. Scientists think this might be done to warn other whales of danger, or as a method of feeding.[14]
Related pages
[change|change source]References
[change|change source]
- ↑Mead, James G. and Brownell, Robert L. Jr. 2005. Order Cetacea (pp. 723-743). In Wilson, Don E. and Reeder, DeeAnn M. (eds)Mammal species of the world: a taxonomic and geographic reference.3rd ed, Baltimore: Johns Hopkins University Press, 2 vols.ISBN978-0-8018-8221-0.OCLC 62265494
- ↑Buskey, Theresa (1996). Alan Christopherson, M.S. (ed.).History and Geography.L.I.F.E.P.A.C. Alpha Omega Publications, Inc.ISBN978-1-58095-156-2.Retrieved1 April2010.
- ↑Anon (25 January 2005)."Scientists find missing link between the whale and its closest relative, the hippo".PhysOrg.com.Archivedfrom the original on 6 June 2011.Retrieved6 May2010.
- ↑Northeastern Ohio Universities Colleges of Medicine and Pharmacy."Whales descended from tiny deer-like ancestors".ScienceDaily.Archivedfrom the original on 24 April 2015.Retrieved21 December2007.
- ↑Dawkins, Richard(2004).The Ancestor's Tale: a pilgrimage to the dawn of life.Boston: Houghton Mifflin Company.ISBN0-618-00583-8.
- ↑"How whales learned to swim".BBC News. 8 May 2002.Archivedfrom the original on 24 August 2011.Retrieved20 August2006.
- ↑University of Plymouth (26 May 2020)."Scientists reveal new fundamental principles governing diving in animals"(Press release). Eurekalert.org. Archived fromthe originalon 4 June 2020.Retrieved1 June2020.
- ↑Wilco C. E. P. Verberk; Piero Calosi; François Brischoux; John I. Spicer; Theodore Garland; David T. Bilton (27 May 2020)."Universal metabolic constraints shape the evolutionary ecology of diving in animals".Proceedings of the Royal Society B: Biological Sciences.287(1927). Proceedings of the Royal Society B.doi:10.1098/rspb.2020.0488.ISSN0962-8452.PMC7287373.PMID32453989.
- ↑Anon (24 May 2001)."Do whales and dolphins sleep?".How Stuff Works.Discovery Communications.Archivedfrom the original on 13 February 2010.Retrieved14 February2010.
- ↑"Blue Whale assessment and status report"(PDF).Archivedfrom the original on 15 September 2014.Retrieved30 August2011.
- ↑Siebert, Charles (8 July 2009)."Watching whales watching us".New York Times Magazine.Archivedfrom the original on 28 April 2021.Retrieved31 August2017.
- ↑Hooker, Sascha K. (2009). Perrin, William F.; Wursig, Bernd; Thewissen, J.G.M. (eds.).Encyclopedia of Marine Mammals(2nd ed.). Academic Press. p. 1174.ISBN978-0-12-373553-9.Archivedfrom the original on 9 November 2009.Retrieved30 August2011.
- ↑Whitehead, Hal (2003),Sperm whales: social evolution in the ocean,Chicago: University of Chicago Press, p. 181,ISBN0226895173,archivedfrom the original on 5 July 2021,retrieved24 February2022
- ↑Weinrich, Mason T.; Schilling, Mark R.; Belt, Cynthia R. (December 1992), "Evidence for acquisition of a novel feeding behaviour: lobtail feeding in humpback whales,Megaptera novaeangliae",Animal Behaviour,44(6): 1059–1072,doi:10.1016/S0003-3472(05)80318-5,S2CID53270820
Other websites
[change|change source]
- ARKive - images and movies of whales, dolphins and porpoisesArchived2016-04-26 atArchive.today
- American Cetacean Society
- Scottish Cetacean Research & Rescue– some interesting things inTaxonomy
- Cetacea.org homepage
- Walker's Mammals of the World Online - CetaceansArchived2004-10-11 at theWayback Machine
- Whales, dolphins, porpoises and cetaceans forumArchived2008-12-10 at theWayback Machine