Baleen

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Baleen hair is attached to the baleen plate

Baleen (also called whalebone) is a substance made of keratin and is therefore stiff but somewhat elastic. Whalebone is a modification of the epidermis. A bony mineral, hydroxyapatite, is also present in baleen in small amounts, along with traces of manganese, copper, boron, iron, and calcium.

Baleen makes up baleen plates, which are arranged in two parallel rows that look like combs of thick hair; they are attached to the upper jaws of baleen whales. Whales use these combs for filter feeding. Whales are the only vertebrate group to use this method of feeding in great abundance (flamingos and crabeater seals use similar methods, but do not have baleen), and it has allowed them to grow to immense sizes. The Blue Whale, the largest animal ever to live, is a baleen whale.

Depending on the species of whale, a baleen plate can be 0.5 to 3.5 m (2 to 12 ft) long, and weigh up to 90 kg (200 lb). Its hairy fringes are called baleen hair or whalebone-hair. Baleen plates are broader at the gumline (base). The plates have been compared to sieves or Venetian blinds.

The word "Baleen" derives from Early Modern English word meaning "whale". It derives from the Latin balaena and is related to the Greek phallaina, both of which also mean "whale".

[edit] Evolution of baleen

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. This is indicated by skull modifications which are associated with baleen (such as a buttress of bone found beneath the eyes in the upper jaw, and loose lower jaw bones at the chin), being found in fossils from considerably earlier. Currently, baleen is believed to have evolved around thirty million years ago, possibly from a creature with a hard, gummy upper jaw, similar to that found on Dall's porpoise today, which are, at a microscopic level, almost identical to baleen.

Curiously, many early baleen whales also had teeth, but these were likely used only peripherally, or perhaps not at all (again, similar to Dall's porpoise, which catches squid and fish by gripping them against its hard upper jaw).

[edit] Baleen in 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 large volumes of water, which inevitably contains large quantities of the plankton it feeds on. It then shuts its mouth and presses its tongue against its hard upper jaw, forcing the water to pass through the baleen, where the plankton are sieved out. The water is then released, and the prey is swallowed.

[edit] Uses of baleen

Baleen plates were formerly used in buggy whips and parasol ribs, and to stiffen parts of women's stays and dresses, like corsets. Baleen was commonly used to crease paper; its flexibility keeps it from damaging the paper. Its function now has been replaced by plastic. It was also formerly believed that baleen plates could be obtained from whale fins.

[edit] See also

• Baleen whale

[edit] Further reading

• St. Aubin, D.J, R.H. Stinson and J.R. Geraci 1984. "Aspects of the structure and function of baleen, and some effects of exposure to petroleum hydrocarbons". Canadian Journal of Zoology 62: 193-198