Baleen

Baleen, also called baleen plates, is a set of triangular sheets that help certain whales eat. These plates hang inside the mouth of baleen whales and work like a filter. This filter system is often called the "Baleen rack." When the whale opens its mouth to take in water, it pushes the water back out through the baleen. The baleen holds back the food, and the whale then eats it.

Baleen is made of keratin, the same material found in human fingernails, skin, and hair. Each baleen plate is made of many bristles across the upper jaw of the whale. Some whales, such as the bowhead whale, have baleen of different lengths. Others, such as the gray whale, use only one side of their baleen.

Baleen plates can be quite large. Depending on the species, a plate can be 0.5 to 3.5 m (1.6 to 11.5 ft) long and weigh up to 90 kg (200 lb). The hairy fringes along the plates are called baleen hair, whalebone hair, or baleen bristles. In sei whales, these bristles are very hard because they are highly calcified, which makes them stiffer. The plates are wider at the gumline, or base. They have been compared to sieves or Venetian blinds.

When people use baleen for different purposes, it is usually called whalebone. This is a misnomer, because baleen is not actually bone.

Etymology

The word "baleen" comes from the Latin word bālaena. This word is related to the Greek word phalaina. Both words mean "whale".

Evolution

The oldest true fossils of baleen are only about 15 million years old. Baleen rarely turns into fossil, so scientists think it began much earlier. Clues come from skull changes in older fossils. One clue is a buttress of bone in the upper jaw below the eyes. Another is loose lower jaw bones at the chin. Baleen is thought to have evolved about 30 million years ago. It may have grown from a firm, gummy upper jaw, like the one a Dall's porpoise has. Under a microscope, that jaw looks very similar to baleen. Baleen likely began to evolve and spread during the Early Oligocene. At that time, Antarctica separated from Gondwana, and the Antarctic Circumpolar Current formed. The current kept warm water away from Antarctica, which made ocean life more productive. Where warm and cold water met, there were big differences in temperature, salinity, light, and nutrients.

The change from teeth to baleen probably happened stepwise. First, whales had teeth. Then they had a mix of teeth and baleen. Finally, they had only baleen. Modern mysticetes have teeth before they are born, and baleen plate germs grow inside them. Later, they lose their teeth and have only baleen as young and adult whales. Developing mysticetes do not make tooth enamel. This gene stopped working as a pseudogene at some point, probably about 28 million years ago. This shows that teeth were part of their early past. Using parsimony, scientists think the common ancestor of aetiocetids and edentulous mysticetes had small openings in the jaw called lateral nutrient foramina. These may have carried blood vessels and nerves to growing baleen. Later research suggests that the baleen of Aetiocetus grew in bundles between widely spaced teeth. This would make it a link between odontocetes and mysticetes. Other changes, like skull shape and throat elasticity, also helped whales filter food from water. These changes probably did not all happen at once. So Oligocene aetiocetids may have had some older and some newer feeding traits, making them mosaic taxa. Their baleen may have grown before their teeth were lost. Or filter-feeding traits may have first developed for other purposes. Early baleen whales with teeth probably used them only a little, or not at all, similar to Dall's porpoise. Researchers have studied the phylogenetic history of mysticetes closely, but scientists still debate many parts of it.

Filter feeding

A baleen whale uses its baleen plates when it feeds. The whale opens its mouth wide and scoops up large groups of food, such as krill, copepods, small fish, and sometimes birds that are near the shoals. It takes in a lot of water with the food.

Next, the whale partly closes its mouth and presses its tongue against its upper jaw. This pushes the water out sideways through the baleen. The baleen catches the food, and the whale swallows it.

Mechanical properties

Whale baleen is made mostly of mineralized keratin. It forms parallel plates that hang down from the whale's mouth. Baleen is strong and flexible, which made it a popular material for many uses (see: § Human uses). Its structure looks like a tube with a hollow inner core, surrounded by a tubular layer. The tubes are between 60 and 900 micrometres across. The tubular layer had about 2.7 times more calcium than the outer solid shell. The elastic modulus is 270 MPa lengthwise and 200 MPa across. This may be because of how the tubes are packed together.

Wet and dry baleen respond very differently to pressure. When squeezed parallel to the plates, dry samples reached about 140 MPa at 0.07 strain. Wet samples reached about 20 MPa. Wetness greatly reduced the response. Cracks also behave differently across the plates. Across the plates, cracks are redirected along the tubes, which helps baleen resist breaking.

Human uses

People used baleen, which is often called "whalebone," to make many items that needed to be bendy and strong. These included baskets, backscratchers, collar stiffeners, buggy whips, parasol ribs, switches, crinoline petticoats, farthingales, busks, and corset stays. It was also used for some pieces of armour. Baleen was often used to crease paper, because its flexibility kept it from tearing the paper. Sometimes it was also used in cable-backed bows. Today, synthetic materials, especially plastic and fiberglass, are usually used for similar purposes. Dutch cabinetmakers also used baleen to make pressed reliefs.

In the United States, the Marine Mammal Protection Act of 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".