Baleen
Baleen is a
Depending on the species, a baleen plate can be 0.5 to 3.5 m (1.6 to 11.5 ft) long, and weigh up to 90 kg (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, with 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.
As a material for various human uses, baleen is usually called whalebone, which is a misnomer.
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 because baleen rarely fossilizes, but 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 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.[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
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
Filter feeding
A whale's baleen plates play the most important role in its filter-feeding process. 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.
Mechanical properties
Whale baleen is the mostly mineralized keratin-based bio-material consisting of parallel plates suspended down the mouth of the whale. Baleen's mechanical properties of being strong and flexible made it a popular material for numerous applications requiring such a property (see Human uses section).
The basic structure of the whale baleen has been described as a tubular structure with a hollow medulla (inner core) enclosed by a tubular layer with a diameter varying from 60 to 900 microns, which had approximately 2.7 times higher calcium content than the outer solid shell. The
Hydrated versus dry whale baleen also exhibit significantly different parallel and perpendicular compressive stress to compressive strain response. Although parallel loading for both hydrated and dry samples exhibit higher stress response (about 20 MPa and 140 MPa at 0.07 strain for hydrated and dry samples respectively) than that for perpendicular loading, hydration drastically reduced the compressive response. [6]
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
People formerly used baleen (usually referred to as "whalebone") for making numerous items where flexibility and strength were required, including
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".[10]
As a habitat
Baleen serves as a habitat for some species from the gastropod families Pyropeltidae, Cocculinidae, Osteopeltidae, and Neolepetopsidae.[11]
See also
- Sullivan's Island
References
- .
- PMID 20392736. Archived from the original(PDF) on 2011-12-25.
- ^ PMID 18266181.
- S2CID 21797084.
- PMID 17015308.
- PMID 30450716.
- ^ Lee Raye, “Evidence for the use of whale-baleen products in medieval Powys, Wales”, Medieval Animal Data Network (blog on Hypotheses.org), June, 26th, 2014. online
- ^ BREEBAART, Iskander; VAN GERVEN, Gert (2013). "Pressed baleen and fan-shaped ripple mouldings by Herman Doomer". Eleventh International Symposium on Wood and Furniture Conservation Amsterdam 9–10 November 2012. Amsterdam. Stichting Ebenist: 62–74.
- ^ Fisheries, NOAA (2021-04-27). "Marine Mammal Protection Act | NOAA Fisheries". NOAA. Retrieved 2021-05-08.
- S2CID 86122448.
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" (PDF). Canadian Journal of Zoology. 62 (2): 193–8. doi:10.1139/z84-032.
- Meredith, Robert W.; Gatesy, John; Cheng, Joyce; Springer, Mark S. (2010). "Pseudogenization of the tooth gene enamelysin (MMP20) in the common ancestor of extant baleen whales". Proceedings of the Royal Society B: Biological Sciences. 278 (1708): 993–1002. PMID 20861053.
- "How baleen whales lost a gene and their teeth". Thoughtomics. Archived from the original on 2011-03-22.
External links
- . New International Encyclopedia. 1905.
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