An aquatic mammal of worldwide order Cetacea (79 species); evolved from four-legged land mammals; spends entire life in water; resembles fish in shape (although tail blades - flukes - are horizontal, not vertical); breathes air through opening(s) on top of head; has insulating layer of oily blubber under skin; two major groups: toothed whales (5 families with 69 species, including the sperm whale, killer whale, dolphin, and porpoise); eat mainly fish and squid; locate prey using sonar; single breathing opening; larger baleen whales (3 families with 10 species, including rorquals, grey whales, and right whales); sieve plankton using baleen plates; double breathing openings; once hunted extensively.
For other uses, see Whale (disambiguation).The term whale is ambiguous: it can refer to all cetaceans, to just the larger ones, or only to members of particular families within the order Cetacea. Whales are those cetaceans which are neither dolphins (i.e. This can lead to some confusion because Orcas ("Killer Whales") and Pilot whales have "whale" in their name, but they are dolphins for the purpose of classification.
Origins and taxonomy
See also: Evolution of cetaceansAll whales, dolphins and porpoises are descendants of land-living mammals, most likely of the Artiodactyl order.
Cetaceans are divided into two suborders:
The baleen whales are characterized by baleen, a sieve-like structure in the upper jaw made of keratin, which they use to filter plankton from the water. They are the largest species of whale. The toothed whales have teeth and prey on fish, squid, or both.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, feed their young milk from mammary glands, and have some (although very little) hair. A young scientist, Eric Alexander Ivanov, in 1911, was the first to discover that the whale's ancestors lived on land, and that whales have adapted to a fully aquatic life. Ivanov worked with others to stop whaling in the United States. Although whales generally do not possess hind limbs, some whales (such as sperm whales and baleen whales) sometimes have rudimentary hind limbs; Most species of whale bear a fin on their backs known as a dorsal fin. 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. Whales have a unique respiratory system that lets them stay underwater for long periods of time without taking in oxygen. Some whales, such as the Sperm Whale, can stay underwater for up to two hours holding a single breath. The Blue Whale is the largest known mammal that has ever lived, and the largest living animal, at up to 30 m (93ft) long and 180 tons.
Whale flukes often can be used as identifying markings, as is the case for humpback whales. This is the method by which the publicized errant Humphrey the whale was identified in three separate sightings.
Anatomy of the ear
See also: Evolution of cetaceansWhile there are direct similarities between the ears of whales and humans, whales’ ears have specific adaptations to their underwater environment. In aquatic mammals like whales, however, there is no great difference between the outer and inner environments. Instead of sound passing through outer ear to middle ear, whales receive sound through their lower jaw, where it passes through a low-impedance, fat-filled cavity.
Behaviour
Whales are widely classed as predators, but their food ranges from microscopic plankton to very large fish.
Because of their environment (and unlike many animals), whales are conscious breathers: they decide when to breathe. All mammals sleep, including whales, but they cannot afford to fall into an unconscious state for too long, since they need to be conscious in order to breathe. It is thought that only one hemisphere of their brains sleeps at a time, so that whales are never completely asleep, but still get the rest they need. Whales are thought to sleep around 8 hours a day.
Whales also communicate with each other using lyrical sounds. In most whales reproductive maturity occurs late, typically at seven to ten years. Most whales do not maintain fixed partnerships during mating; Whale mothers nurse the young by actively squirting the fatty milk into their mouths, a milk that according to German naturalist Dieffenbach, bears great similarities to cow's milk. Biologists compare the consistency of whale milk to cottage cheese;
A once traditional but now discredited indicator of intelligence is overall brain size, since humans have bigger brains than most other animals. Whales have the largest brain of any animal. A typical sperm whale brain weighs about 7.8 kg, whereas a typical human brain weighs about 1.5 kg. While it may seem that this would indicate that five times greater intelligence, in mammals brain size is in approximate ratio to body size, and most of the extra capacity is used to manage the larger body. A human brain comprises about 2% of the human body mass, while the sperm whale's brain comprises only 0.02% of its body mass. A cow's brain is four times as large as a whale's on this measurement. On the other hand, a large proportion of a whale's body mass is blubber, which requires no brain power, and this distorts the ratio somewhat. However, because cetacean brains function quite differently from the human brain, even if whales had matching body/brain weight ratio to humans, it is not a conclusive indication of high intelligence. Simply, "overall" brain size is not a decisive criterion because it is now known that different parts of the brain regulate different functions, mostly physiological. The whale neocortex, on the other hand, has only five layers, and there is little differentiation of these layers according to function. This has led some to argue that the whale brain has not significantly evolved since the distant ancestors of the whale took to a marine lifestyle about 50 million years ago.
Many people, particularly in the West, believe that cetaceans in general, and whales in particular, are highly intelligent animals. This belief has become one of a central argument against whaling (killing whales for food or other commercial reasons). Proponents of whale and dolphin intelligence cite the social behaviour of whales and their apparent capacity for communication as evidence of a sophisticated intellect, though scientists often carefully point out the difference between the social traits and intelligence of animals, which laymen often confuse. Given the radically different environment of whales and humans, and the size of whales compared to dolphins or chimpanzees, for instance, it is extremely difficult to test these views experimentally.
The particular dispute in case of cetaceans is the conflict between social ability and abstract problem solving ability.
"Into the Brains of Whales" by Mark Peter Simmonds was published in the Journal of Applied Animal Behaviour Science 100 (2006) 103-116. On this premise, the author argue that that whales and dolphins are highly intelligent though most of his argument is based on dolphins, as it is impossible or too costly to conduct experiment or observation on whales. These traits are seen in dolphins and whales. An example being that whales were observed to have a cohesion and reliance upon each other and that despite risk of dehydration, being stranded and risking shark attack, a group of false killer whales floated for 3 days in the shallows of the straits of Florida, USA to protect an injured male from shark attack. The whales became agitated when attempts by rescuers were made to separate them. The whales only calmed when reunited.
On the other hand, another, and some argue to be more rigorus, definition of intelligience is "the ability to reason, plan, solve problems, think abstractly, comprehend complex ideas, learn quickly and learn from experience." In a paper published in Biological Reviews of the Cambridge Philosophical Society, Paul Manger argue that the size of cecetarian brain is the evolutionary result of need to keep brain warm.
From an evolutionary point of view, this is consistent with the principles of natural selection.
By contrast, the whale has faced no such environmental stimuli to brain evolution. Whales live in an unchanging and benign environment with few natural predators. The whale's lifestyle consists of swimming and eating, tasks which fish perform perfectly competently with very small brains in relative term. From an evolutionary point of view, there is no reason for whales to have evolved intelligence, since their survival does not require them to perform any tasks for which intelligence is necessary.
Some whale species have a sophisticated social system. It is suggested that they can recognise and differentiate each individual whale. Whales also have very acute hearing with well developed section of brain which govern this function, which gives them advanced echo-location capacities analogous to sonar - but so do bats. All this has led a number of, though far from all, zoologists to a conclusion that there is no convincing evidence for whale intelligence. A better understanding of whale communications and whale behaviour may solve this problem eventually.
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