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Baleen

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Title: Baleen  
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Subject: Bowhead whale, Basket, History of corsets, Whaling, Baleen whale
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Baleen

Photo displaying dozens of baleen plates. The plates face each other, and are evenly spaced at approximately 0.25 inches (1 cm) intervals. The plates are attached to the jaw at the top, and have hairs at the bottom end.
Baleen hair is attached to each baleen plate

Appearance of baleen hair in a whale's open mouth
cross-section of jaw showing bone a, gum b, rigid plate c and frayed baleen hairs d and e

Baleen is a filter-feeder system inside the mouths of baleen whales. The baleen system works when a whale opens its mouth underwater and the whale takes in water. The whale then pushes the water out, and animals such as krill are filtered by the baleen and remain as food source for the whale. Baleen is similar to bristles and is made of keratin, the same substance found in human fingernails and hair. Some whales, such as the bowhead whale, have longer baleen than others. Other whales, such as the gray whale, only use one side of their baleen. These baleen bristles are arranged in plates across the upper jaw of the whale. Baleen is often called whalebone, but that name also can refer to the normal bones of whales, which have often been used as a material, especially as a cheaper substitute for ivory in carving.

Depending on the species, a baleen plate can be 0.5 to 3.5 metres (1.6 to 11.5 ft) long, and weigh up to 90 kilograms (200 lb). Its hairy fringes are called baleen hair or whalebone-hair. They are also called baleen bristles, which in sei whales are highly calcified, calcification functioning to increase their stiffness.[1][2] Baleen plates are broader at the gumline (base). The plates have been compared to sieves or Venetian blinds.

Contents

  • Etymology 1
  • Evolution 2
  • Filter feeding 3
  • Human uses 4
  • As a habitat 5
  • See also 6
  • References 7
  • Further reading 8

Etymology

The word baleen derives from the Latin bālaena, related to the Greek phalaina – both of which mean "whale".

Evolution

The oldest true fossils of baleen are only 15 million years old, but baleen rarely fossilizes, and scientists believe it originated considerably earlier than that.[3] This is indicated by baleen-related skull modifications being found in fossils from considerably earlier, including a buttress of bone in the upper jaw beneath the eyes, and loose lower jaw bones at the chin. Baleen is believed to have evolved around thirty million years ago, possibly from a hard, gummy upper jaw, like the one a Dall's porpoise has; it closely resembles baleen at the microscopic level. The initial evolution and radiation of baleen plates is believed to have occurred during Early Oligocene when Antarctica broke off from Gondwana and the Antarctic Circumpolar Current was formed, increasing productivity of ocean environments.[4] This occurred because the current kept warm ocean waters away from the area that is now Antarctica, producing steep gradients in temperature, salinity, light, and nutrients where the warm water meets the cold.[5]

The transition from teeth to baleen is proposed to have occurred elasticity. It would be highly unlikely for all of these changes to occur at once. Therefore, it is proposed that Oligocene aetiocetids possess both ancestral and descendent character states regarding feeding strategies. This makes them a mosaic taxa, showing that either baleen evolved before dentition was lost or that the traits for filter feeding originally evolved for other functions. It also shows that the evolution could have occurred gradually because the ancestral state was originally maintained. Therefore, the mosaic whales could have exploited new resources using filter feeding while not abandoning their previous prey strategies. The result of this stepwise transition is apparent in modern-day baleen whales, because of their enamel pseudogenes and their in utero development and reabsorbing of teeth.[3]

If it is true that many early baleen whales also had teeth, these were probably used only peripherally, or perhaps not at all (again like Dall's porpoise, which catches squid and fish by gripping them against its hard upper jaw). Intense research has been carried out to sort out the evolution and phylogenetic history of mysticetes, but there is still much debate surrounding this issue. More work needs to be done to characterize extinct ancestral fossils so that future scientists will be able to piece together a more accurate phylogenetic tree.

Filter feeding

A whale's baleen plates play the most important role in its filter-feeding process. In order to feed, a baleen whale opens its mouth widely and scoops in dense shoals of prey (such as krill, copepods, small fish and sometimes birds that happen to be near the shoals), together with large volumes of water. It then partly shuts its mouth and presses its tongue against its upper jaw, forcing the water to pass out sideways through the baleen, thus sieving out the prey which it then swallows.

Human uses

Inupiat baleen basket, with an ivory handle, made by Kinguktuk (1871–1941) of Barrow, Alaska. Displayed at the Museum of Man, San Diego, California.

People formerly used baleen (usually referred to as "whalebone") for making numerous items where flexibility and strength were required, including backscratchers, collar stiffeners, buggy whips, parasol ribs and as corset stays. It was commonly used to crease paper; its flexibility kept it from damaging the paper. It was also occasionally used in cable-backed bows. Synthetic materials are now usually used for similar purposes, especially plastic and fibre glass. It is not to be confused with whale's bone meaning the bones of whales, used in carving, for cutlery handles and other uses for the bones of various large species.

As a habitat

Baleen serves as a habitat for some species from the gastropod families Pyropeltidae, Cocculinidae, Osteopeltidae and Neolepetopsidae.[6]

See also

References

  1. ^ Fudge, Douglas S.; Szewciw, Lawrence J.; Schwalb, Astrid N. (2009). "Morphology and Development of Blue Whale Baleen: An Annotated Translation of Tycho Tullberg's Classic 1883 Paper" (PDF). Aquatic Mammals 35 (2): 226–52.  
  2. ^ Szewciw, L. J.; De Kerckhove, D. G.; Grime, G. W.; Fudge, D. S. (2010). "Calcification provides mechanical reinforcement to whale baleen -keratin" (PDF). Proceedings of the Royal Society B: Biological Sciences 277 (1694): 2597–605.  
  3. ^ a b Deméré, Thomas; Michael R. McGowen; Annalisa Berta; John Gatesy (September 2007). "Morphological and Molecular Evidence for a Stepwise Evolutionary Transition from Teeth to Baleen in Mysticete Whales". Systematic Biology 57 (1): 15–37.  
  4. ^ Marx, Felix G. (19 February 2010). "Climate, critters and cetaceans: cenozoic drivers of the evolution of modern whales". Science 327: 993–996. 
  5. ^ Fitzgerald, Erich M.G. (15 August 2006). "A bizarre new toothed mysticete (Cetacea) from Australia and the early evolution of baleen whales". Proceedings of the Royal Society: Biological Sciences 273: 2961. 
  6. ^ McLean, James H. (2008). "Three New Species of the Family Neolepetopsidae (Patellogastropoda) from Hydrothermal Vents and Whale Falls in the Northeastern Pacific". Journal of Shellfish Research 27: 15–20.  

Further reading

  • St. Aubin, D. J.; Stinson, R. H.; Geraci, J. R. (1984). "Aspects of the structure and composition of baleen, and some effects of exposure to petroleum hydrocarbons". Canadian Journal of Zoology 62 (2): 193–8.  
  • Meredith, Robert W.; Gatesy, John; Cheng, Joyce; Springer, Mark S. (2010). ) in the common ancestor of extant baleen whales"MMP20"Pseudogenization of the tooth gene enamelysin (. Proceedings of the Royal Society B: Biological Sciences 278 (1708): 993–1002.  
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