header: Cetaceans (Whales)
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Mammalian order Cetacea

GENERAL BIOLOGY

Cetaceans are mammals which spend all their lives in water, and have now evolved many adaptations to this way of life. The body is streamlined, with no hind limbs, reduced forelimbs and a powerful horizontal tail for propulsion. The "nostrils" have become blow holes at the top of the head (except in the Sperm Whale, where it is at the front of the head) to facilitate respiration whilst travelling through water.

The baleen whales have a series of baleen plates which are used to sieve food from the water. These may differ from species to species, their size, shape and number relating to the preferred food.

The dentition of the toothed whales are also roughly related to feeding habits, with the squid eaters having few or no visible teeth, and those with a more varied diet, particularly those where schooling fish are included, having a generally longer snout and many teeth.

The majority of the large cetacean species are baleen whales, including the Blue Whale (up to 30 m), although there are smaller baleen whales, including the 10 m Minke Whale and the 6 m Pygmy Right Whale. Many baleen whales travel long distances every year, between summer feeding grounds in polar waters and winter breeding grounds in the tropics. In general, baleen whales seem to live in small social groups, although these can join to form large herds at rich feeding grounds.

The range in size among toothed whales is wide, from the 18 m (male) Sperm Whale to the smallest dolphins and porpoises at less than 2 m. They have extremely varied habits; some travel long distances between summer feeding grounds and wintering areas every year, but others are relatively sedentary, perhaps only ranging over tens of kilometres in their lifetimes. Their social life is also highly varied; some species living in small groups or usually alone, and others in schools of several hundred (although these may be composed of a number of smaller social units).

The fossil history of the cetaceans is incomplete and controversial. In general it seems that they evolved from land mammals which may have returned to the water some 70-90 million years ago. The Archaeocetes flourished 45-55 million years ago and the modern forms have been present since 10-12 million years ago. Cetaceans have exploited all types of productive marine, estuarine, and major riverine habitat. They have adapted to be able to propel themselves through the water at speeds and to depths sufficient to escape predators and catch prey; exchange air without interrupting the smooth forward motion; maintain a fairly constant core body temperature in an environment that readily dissipates heat; and bear young in water.

Vision in air and water varies with species, from some river dolphins which are nearly blind and can distinguish light from dark to some dolphins with apparently excellent vision in both media. Most species are vocal, producing calls and whistles which may have a social function, such as the "song" of the Humpback Whale, the individual "signature whistles" of Bottlenose Dolphins and the "pod identity" call of the Killer Whales. Many toothed whales are known to echo-locate, using pulses of high frequency sound to explore their environment and seek and stun their prey.


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