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Whale
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Whale

Whales are the largest species of exclusively aquatic placental mammals, members of the order Cetacea, which also includes dolphins and porpoises. The term whale is ambiguous: it can refer to all cetaceans, just the largest ones, or only to members of particular families within the order Cetacea. This latter definition is the one followed within Wikipedia. Whales are those cetaceans which are neither dolphins (i.e. members of the families Delphinidae or Platanistoidae) or porpoises. This can lead to some confusion as Orca ("Killer Whales") and Pilot Whales have "whale" in their name, but are dolphins from the perspective of classification. Cetologists tend not to worry too much about making a distinction.

Table of contents
1 Taxonomy
2 Anatomy
3 Behaviour
4 Reproduction
5 The Evolution of Whales
6 Whales and Humans
7 See also
8 Further reading
9 External links

Taxonomy

Cetaceans are divided into two suborders: A complete up-to-date taxonomical listing of all cetacean species, including all whales is maintained at the Cetacea article.

Anatomy

Like all mammals, whales breathe air into lungs, are warm-blooded (i.e., endothermic), breast-feed their young, and have some (very little) hair. The whales' adaptions to a fully aquatic life are quite conspicuous: The body is fusiform, resembling that of a fish. The forelimbs, also called flippers, are paddle-shaped. The end of the tail holds the fluke, which provides propulsion by vertical movements. Whales do not possess hind limbs, small bones inside the body are the only remains of the pelvis. Most species of whales 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 one blowhole. When breathing out 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 any oxygen. Some whales, such as the Sperm Whale, can stay underwater for up to two hours in a single breath.

Especially noteworthy is the Blue Whale, the largest animal that has ever lived. It may be up to 30 meters long and weigh 180 tons.

Behaviour

Main article: Whale behaviour

Whales are broadly classed as predators, but their food ranges from microscopic plankton to very large fish. The male is called a bull; the female, a cow; and the young, a calf.

Because of their environment, whales are conscious breathers: They have to decide when to breath. So how do they sleep? All mammals sleep, and so do whales, but they cannot afford to fall in unsconscious state of sleep for too long periods of time, since they need to be conscious in order to breath. The solution is that only one hemisphere of the brains of the whale sleeps at the time, so whales are never completely asleep, but still get the rest they need. Whales "sleep" around 8 hours a day.

Reproduction

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, provided 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 minimizied. Whale mothers nurse the young by actively squirting the fatty milk into their mouth.

The Evolution of Whales

Whales are the descendants of land-living mammals, and remnants of their terrestrial origins can be found in the fact that they must breathe air from the the surface; in the bones of their fins, which look like huge, jointed hands; and in the vertical movement of their spines, characteristic more of a running mammal than of the horizontal movement of fish. The question of how land animals evolved into ocean-going behemoths has been a mystery for a long time, owing to gaps in the fossil record. However, recent discoveries in Pakistan have managed to solve many of these mysteries, and it is now possible to see several stages in the transition of the ceteceans from land to sea.

Earliest Origins: Mesonychids, Hippos or Artiodactyls?

Before the recent discoveries in Pakistan, one popular theory of cetecean evolution was that whales were related to the Mesonychids, an extinct order of carnivorous ungulates (hoofed animals), which looked rather like wolves with hooves. These animals possessed unusual triangular teeth that are similar to those of whales. For this reason, scientists had long believed that whales evolved from a form of Mesonychid.

However, DNA analysis generated an alternative hypothesis. Whale DNA is more similar to that of the Hippopotamids than to any other living animal. Therefore, a debate arose as to whether hippos or mesonychids were the closest relatives if the whales.

The recent discovery of Pakicetus, the earliest proto-whale (see below) has helped to settle the debate. The skeletons of Pakicetus demonstrate that whales did not derive directly from Mesonychids. Instead, they are a form of Artiodactyl (another type of ungulate) that began to take to the water after the Artiodactyl family split from the Mesonychids. In other words, the proto-whales were early Artiodactyls that retained aspects of their Mesonychid ancestry (such as the triangular teeth) which modern Artiodactyls have since lost.

Hippos are artiodactyls too, but the new discovery suggests that the origins of whales and hippos are not directly related. The reason for the physical and genetic similarities between them is that hippos split off from the main Artiodactyl line shortly after the proto-whales did, and thus, like whales, hippos retain some characteristics of early Artiodactyls. Both hippos and whales are Artiodactyls that became adapted to life in the water, but they did so separately and evolved in quite different directions.

Pakicetids: The Earliest Ceteceans

The Pakicetids are the earliest known proto-whales; they lived around 52 million years ago. They looked rather like dogs with long, thick tails. It is not known exactly how the they lived, but they may have roamed the seashore or hunted in rivers. What links the Pakicetids to whales is the structure of their ears, which contain an adaptation to underwater hearing that is possessed only by whales. It seems that the Pakicetids were amphibious carnivores which, thanks to their remarkable ears, were able to hear better in the water than other aquatic mammals. This adaptation began the journey that would lead to the whales.

Ambulocetids and Remingtonocetids

The most remarkable of the recent discoveries in Pakistan has been Ambulocetus, which looked like a three-metre long mammalian crocodile. Ambulocetus was clearly amphibious, as its back legs are better adapted for swimming than for walking on land, and it probably swam by undulating its back vertically, as otters, seals and whales do. It has been speculated that Ambulocetids hunted like crocodiles, lurking in the shallows to snatch unsuspecting prey.

A smaller cousin of Ambulocetus was the Remingtonocetid family, which had longer snouts than Ambulocetus', and were slightly better adapted for underwater life. It has been speculated that they lived like modern sea otters, hunting for fish in the shallows.

The Protocetids

The Protocetids, which include Rodhocetus and Artiocetus, are another recent discovery. They lived around 45 million years ago. Their principal adaptation was flukes (horizontal bars) on their tails, which enable faster swimming; however, they retained substantial hind legs. They lived in shallow seas, and may have had a similar lifestyle to seals, or even dolphins; it is not known whether they ever came onto the land.

Basilosaurids and Dorudontids: Fully Marine Ceteceans

Basilosaurus (discovered in 1840 and initially mistaken for a lizard) and Dorudon lived around 38 million years ago, and were fully recognisable whales which lived entirely in the ocean. Basilosaurus was a monstrous creature, up to 18m long, while Dorudontids were dolphin-sized, about 5m long. Although they look very much like modern whales, Basilosaurids and Dorudontids lacked the 'melon organ' that allows their descendants to sing and use ultrasound. They also had small brains; this suggests they were solitary and didn't have the complex social structure of modern whales. Most remarkable of all, Basilosaurus retained two tiny, useless hind limbs, a small reminder of the lives of their ancestors.

Whales and Humans

Conservation

Most species of large whales are endangered as a result of whaling. However, most affected are the river dolphins by changes to the rivers they inhabitate.

Whaling

Main article Whaling

For centuries large whales have been hunted for oil, meat, baleen and ambergris (a perfume ingredient from the intestine of sperm whales). Until the middle of the 20th century, whaling left many populations nearly or fully extinct. The International Whaling Commission introduced an open ended moratorium on all commercial whaling in 1986. For various reasons some exceptions to this moratorium exist; current whaling nations are Norway, Iceland and Japan and the aboriginal communities of Siberia, Alaska and northern Canada. For details, see whaling.

Bycatch

Several species of small whales are caught as bycatch in fisheries. Especially during the tuna fishery in the Pacific each year thousands of dolphins drown in the nets. In many countries, small whales are hunted for food, oil or bait meat.

Sonar

Environmentalists have long argued that some cetaceans including whales are endangered by sonar and especially by the very powerful sonar used by the US defense department. British scientists have recently suggested (in the journal Nature) that the sonar is connected to whale beachings and to signs that the beached whales have experienced decompression sickness (see a BBC report about the Nature article or the Nature article itself (requires subscription)). Mass whale beachingss do occur naturally amongst many species and in fact the frequency and size of beachings around the world, recorded over the last 1000 years in religious tracts and more recently in scientific surveys, has been used to estimate the changing population size of various whale species, under that assumption that the proportion of the total whale population beaching in any one year is constant. Despite the concerns raised about sonar as mentioned above which may invalidate this assumption, this population estimate technique is still popular today [1].

Whales in culture

Whales in the Bible

The Bible mentions whales four times: Genesis 1:21 "And God created great whales"; "Am I a sea, or a whale, that thou settest a watch over me? (Job 7:12); "Thou art like a young lion of the nations, and thou art as a whale in the seas (Ezekiel 32:2); and "For as Jonas [sic] was three days and three nights in the whale's belly; so shall the Son of man be three days and three nights in the heart of the earth" (Matthew 12:40). (All quotations from King James version).

Famously, the Book of Jonah (in the King James and some other translations) does not use the word "whale" at all, referring throughout to a "fish" or a "great fish": "Now the LORD had prepared a great fish to swallow up Jonah. And Jonah was in the belly of the fish three days and three nights." (Jonah 1:17). This detail was used to dramatic effect in Clarence Darrow's cross-examination of fundamentalist William Jennings Bryan in the 1925 Scopes Trial, as depicted in the drama "Inherit the Wind" by Jerome Lawrence and Robert E. Lee.

Herman Melville and Bharat

The hunting of whales is the subject of one of the classics of the English language literary canon, Herman Melville's Moby Dick. Melville classed whales as "a spouting fish with a horizontal tail", despite science suggesting otherwise the previous century. In fact Melville said "the grounds upon which Linnaeus would fain have banished the whales from the waters" but says that when he presented them to "my friends Simeon Macey and Charley Coffin, of Nantucket ... they united in the opinion that the reasons set forth were altogether insufficient. Charley profanely hinted they were humbug."

Capture

A big attraction for ocean parks and zoos is keeping captured small whales, mostly dolphins. Because of their learning ability, they are also used by the military for marine warfare.

See also

Further reading

External links