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A complete up-to-date taxonomical listing of all cetacean species, including all whales is maintained at the Cetacea article.
Like all mammals, whales breathe air into lungs, are warm-blooded (i.e., endothermic), breast-feed their young, and have some (although very little) hair. The whales' ancestors lived on land, and their adaptions to a fully aquatic life are quite striking: The body is fusiform, resembling the streamlined form of a fish. The forelimbs, also called flippers, are paddle-shaped. The end of the tail holds the fluke, or tail fins, which provide propulsion by vertical movement. (Whales do not possess hind limbs: small bones inside the body are the only remains of the pelvis.) Most species of whale bear a fin on their backs. Beneath the skin lies a layer of fat, the blubber. It serves as an energy reservoir and also as insulation. Whales have a four-chambered heart. The neck vertebrae are fused in most whales, which provides stability during swimming at the expense of flexibility.
Whales breathe through blowholes, located on the top of the head so the animal can remain submerged. Baleen whales have two; toothed whales have one. When exhaling after a dive, a spout can be seen from the right perspective, the shape of which differs among the species. Whales have a unique respiratory system that lets them stay underwater for long periods of time without taking in any oxygen. Some whales, such as the Sperm Whale, can stay underwater for up to two hours holding a single breath.
Especially noteworthy is the Blue Whale, the largest known animal that has ever lived. It may be up to 30 meters long and weigh 180 tons.
Main article: Whale behaviour
Whales are broadly classed as predators, but their food ranges from microscopic plankton to very large fish. Males are called bulls; females, cows. The young are called calves.
Because of their environment (and unlike many animals), whales are conscious breathers: They have to decide when to breathe. So how do they sleep? All mammals sleep, and so do whales, but they cannot afford to fall unconscious state for too long, since they need to be conscious in order to breathe. The solution is that only one hemisphere of their brains sleeps at the time, so that whales are never completely asleep, but still get the rest they need. Whales "sleep" around 8 hours a day.
Whale females give birth to a single calf. Nursing time is long (more than one year in many species), which is associated with a strong bond between mother and young. In most whales reproductive maturity occurs late, typically at seven to ten years. This strategy of reproduction spawns few offspring, but provides each with a high rate of survival.
The genital organs are retracted into cavities of the body during swimming, so as to be streamlined and reduce drag. Most whales do not maintain fixed partnerships during mating; in many species the females have several mates each season. At birth the newborn is delivered tail-first, so the risk of drowning is minimized. Whale mothers nurse the young by actively squirting the fatty milk into their mouths.
Whales, along with dolphins and porpoises, are descendants of land-living mammals, most likely of the Artiodactyl order. They entered the water roughly 50 million years ago. See evolution of cetaceans for the details [1].
Most species of large whales are endangered as a result of whaling. However, river dolphins are the most at risk because of changes to the rivers they inhabit. The changes to rivers are mostly human-made i.e. the result of conventional economic development such as building large dams for purposes of irrigation or electricity. For example, the Three Gorges Dam on the Yangtse River in ChinaThis article is on the geographic and cultural entity. For other meanings, see China (disambiguation). China ( Traditional Chinese: , Simplified Chinese: , Hanyu Pinyin: Zhongguo, Wade-Giles: Chung-kuo) is a country in continental East Asia with some oute is threatening the survival of the Yangtse Dolphin. Likewise, large dams being planned on the Irrawaddy River in MyanmarThe Union of Myanmar is a country in Southeast Asia, formerly known as Burma . The name of the country was changed in 1989, and this change of name has been officially recognized by the United Nations. Some national governments, such as the United States and the Mekong River along ThailandThe Kingdom of Thailand is a country in southeast Asia, bordering Laos and Cambodia to the east, the Gulf of Thailand and Malaysia to the south, and the Andaman Sea and Myanmar to the west. Thailand is also known as Siam which was the country's official n and LaosThe Lao People's Democratic Republic is a landlocked country in southeast Asia, bordered by Myanmar (commonly known in the west as Burma) and the People's Republic of China to the northwest, Vietnam to the east, Cambodia to the south, and Thailand to the could lead to the extinction of the endangered Irrawaddy and Mekong Dolphins. Some of these dams like the Nam Theun 2 dam in Laos are also being supported by international nature conservation groups such as the World Conservation UnionThe World Conservation Union or International Union for Conservation of Nature and Natural Resources IUCN is an international organization dedicated to natural resource conservation. Founded in 1948, its headquarters is located in Gland, Switzerland..