right|upright=0.75|frame|Baleen hair is attached to each baleen plate.|alt=Photo displaying dozens of baleen plates. The plates face each other, and are evenly spaced at approximately intervals. The plates are attached to the jaw at the top, and have hairs at the bottom end.
upright=0.75|thumb|Appearance of baleen hair in a whale's open mouth
upright=0.75|thumb|Cross-section of jaw showing bone a, gum b, rigid plate c and frayed baleen hairs d and e
Baleens, also referred to as "Baleen plates", are triangular sheets of keratin that make up a filter-feeding system (the "Baleen rack") inside the mouth of baleen whales. The feeding process starts as the animal opens its mouth to take in water. The whale then pushes the water out through a rack of baleen plates, so as to retain (filter) what will serve as food for the whale. A baleen is similar to a bristle and consists of keratin, the same substance found in human fingernails, skin and hair. Some whales, such as the bowhead whale, have baleen of differing lengths. 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 whales.
Depending on the species, a baleen plate can be long, and weigh up to . Its hairy fringes are called baleen hair or whalebone hair. They are also called baleen bristles, which in sei whales are highly calcified, with calcification functioning to increase their stiffness. Baleen plates are broader at the gumline (base). The plates have been compared to sieves or Venetian blinds.
As a material for various human uses, baleen is usually called whalebone, which is a misnomer.
Etymology
The word "baleen" derives from the Latin , related to the Greek – both of which mean "whale".
Evolution
The oldest true fossils of baleen are only 15 million years old because baleen rarely fossilizes, but scientists believe it originated considerably earlier than that. 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 30 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. 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.
thumb|[[Gray whale calf with mouth open, showing baleen]]
The transition from teeth to baleen is proposed to have occurred stepwise, from teeth to a hybrid to baleen. It is known that modern mysticetes have teeth initially and then develop baleen plate germs in utero, but lose their dentition and have only baleen during their juvenile years and adulthood. However, developing mysticetes do not produce tooth enamel because at some point this trait evolved to become a pseudogene. This is likely to have occurred about 28 million years ago and proves that dentition is an ancestral state of mysticetes. Using parsimony to study this and other ancestral characters suggests that the common ancestor of aetiocetids and edentulous mysticetes evolved lateral nutrient foramina, which are believed to have provided blood vessels and nerves a way to reach developing baleen. Further research suggests that the baleen of Aetiocetus was arranged in bundles between widely spaced teeth. If true, this combination of baleen and dentition in Aetiocetus would act as a transition state between odontocetes and mysticetes. This intermediate step is further supported by evidence of other changes that occurred with the evolution of baleen that make it possible for the organisms to survive using filter feeding, such as a change in skull structure and throat 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 descendant character states regarding feeding strategies. This makes them 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.
Crack formation is also different for both the transverse and longitudinal orientation. For the transverse direction, cracks are redirected along the tubules, which enhances the baleen's resistance to fracture and once the crack enters the tubule it is then directed along the weaker interface rather than penetrating through either the tubule or lamellae.
Human uses
thumb|[[Iñupiat baleen basket, with an ivory handle, made by Kinguktuk (1871–1941) of Utqiaġvik, Alaska, displayed at the Museum of Us, San Diego, California]]
People formerly used baleen (usually referred to as "whalebone") for making numerous items where flexibility and strength were required, including baskets, backscratchers, collar stiffeners, buggy whips, parasol ribs, switches, crinoline petticoats, farthingales, busks, and corset stays, but also pieces of armour. 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 fiberglass. Baleen was also used by Dutch cabinetmakers for the production of pressed reliefs.
In the United States, the Marine Mammal Protection Act in 1972 makes it illegal "for any person to transport, purchase, sell, export, or offer to purchase, sell, or export any marine mammal or marine mammal product".
See also
- John Henry Devereux, a South Carolina architect who used whale jaw bones to adorn the largest mansion on Sullivan's Island