dolphin

A small, toothed whale. The name is usually used for species with a long slender snout (or beak) and streamlined body (though in some dolphins the beak is almost absent). Species with less streamlined bodies and blunt snouts are usually called porpoises (especially in genera Phocoena, Phocoenoides, and Neophocoena); worldwide. The name is also used for fresh water (or river) dolphins (family: Platanistidae, 6 species from S Asia and South America), which have a very long beak used for probing in mud for food. Dolphins have become popular display animals in recent years (especially in dolphinariums), on account of their ready playfulness, graceful swimming, acrobatic ability, and evident intelligence. (Family: Delphinidae, c.28 species.)

?Dolphin
Fossil range: Early Miocene - Recent

Bottlenose Dolphin breaching in the bow wave of a boat

Scientific classification

Kingdom:	Animalia
Phylum:	Chordata
Class:	Mammalia
Order:	Cetacea
Suborder:	Odontoceti
Family:	Delphinidae Gray, 1821

Genera

See article below. It can mean:

Any member of the family Delphinidae (oceanic dolphins), Any member of the families Delphinidae and Platanistoidea (oceanic and river dolphins), Any member of the suborder Odontoceti (toothed whales; these include the above families and some others), Used casually as a synonym for Bottlenose Dolphin, the most common and familiar species of dolphin. Porpoises (suborder Odontoceti, family Phocoenidae) are thus not dolphins in this sense. Orcas and some closely related species belong to the Delphinidae family and therefore qualify as dolphins, even though they are called whales in common language. There are almost forty species of dolphin in seventeen genera. The family Delphinidae is the largest in the Cetacea, and relatively recent: dolphins evolved about ten million years ago, during the Miocene.

Taxonomy

See also: List of dolphins Suborder Odontoceti, toothed whales Family Delphinidae, oceanic Dolphins Genus Delphinus Long-Beaked Common Dolphin, Delphinus capensis Short-Beaked Common Dolphin, Delphinus delphis Genus Tursiops Bottlenose Dolphin, Tursiops truncatus Indo-Pacific Bottlenose Dolphin, Tursiops aduncus Genus Lissodelphis Northern Rightwhale Dolphin, Lissodelphis borealis Southern Rightwhale Dolphin, Lissiodelphis peronii Genus Sotalia Tucuxi, Sotalia fluviatilis Genus Sousa Indo-Pacific Hump-backed Dolphin, Sousa chinensis Chinese White Dolphin (the Chinese variant), Sousa chinensis chinensis Atlantic Humpbacked Dolphin, Sousa teuszii Genus Stenella Atlantic Spotted Dolphin, Stenella frontalis Clymene Dolphin, Stenella clymene Pantropical Spotted Dolphin, Stenella attenuata Spinner Dolphin, Stenella longirostris Striped Dolphin, Stenella coeruleoalba Genus Steno Rough-Toothed Dolphin, Steno bredanensis Genus Cephalorynchus Chilean Dolphin, Cephalorhynchus eutropia Commerson's Dolphin, Cephalorhynchus commersonii Heaviside's Dolphin, Cephalorhynchus heavisidii Hector's Dolphin, Cephalorhynchus hectori Genus Grampus Risso's Dolphin, Grampus griseus Genus Lagenodelphis Fraser's Dolphin, Lagenodelphis hosei Genus Lagenorhyncus Atlantic White-Sided Dolphin, Lagenorhynchus acutus Dusky Dolphin, Lagenorhynchus obscurus Hourglass Dolphin, Lagenorhynchus cruciger Pacific White-Sided Dolphin, Lagenorhynchus obliquidens Peale's Dolphin, Lagenorhynchus australis White-Beaked Dolphin, Lagenorhynchus albirostris Genus Orcaella Australian Snubfin Dolphin, Orcaella heinsohni Irrawaddy Dolphin, Orcaella brevirostris Genus Peponocephala Melon-headed Whale, Peponocephala electra Genus Orcinus Killer Whale, Orcinus orca Genus Feresa Pygmy Killer Whale, Feresa attenuata Genus Pseudorca False Killer Whale, Pseudorca crassidens Genus Globicephala Long-finned Pilot Whale, Globicephala melas Short-finned Pilot Whale, Globicephala macrorhynchus Family Platanistoidea, River Dolphins Genus Inia Boto (Amazon River Dolphin), Inia geoffrensis Genus Lipotes Chinese River Dolphin (Baiji), Lipotes vexillifer Genus Platanista Ganges River Dolphin, Platanista gangetica Indus River Dolphin, Platanista minor Genus Pontoporia La Plata Dolphin (Franciscana), Pontoporia blainvillei

Six species in the family Delphinidae are commonly called "whales" but are strictly speaking dolphins.

Melon-headed Whale, Peponocephala electra Killer Whale, Orcinus orca Pygmy Killer Whale, Feresa attenuata False Killer Whale, Psudoorca crassidens Long-finned Pilot Whale, Globicephala melas Short-finned Pilot Whale, Globicephala macrorhynchus

Genetic evolution and anatomy of dolphins

See also: Evolution of cetaceans

Dolphins, along with whales and porpoises, are thought to be descendants of terrestrial mammals, most likely of the Artiodactyl order. A recent theory however disputes the existence of a neural basis for dolphin intellect, suggesting instead that the large brain is only an adaptation to living in cold water.

Senses

Most dolphins have acute eyesight, both in and out of the water, and their sense of hearing is superior to that of humans. However, dolphins lack an olfactory nerve and thus have no sense of smell, but they can taste and do show preferences for certain kinds of fish. Since dolphins spend most of their time below the surface normally, just tasting the water could act in a manner analogous to a sense of smell.

Dolphin behavior

See also: Whale behavior

Dolphins are often regarded as one of Earth's most intelligent species, though it is hard to say just how intelligent dolphins are as straightforward comparisons of species' relative intelligence are complicated by differences in sensory apparatus, response modes, and nature of cognition.

Dolphins often leap above the water surface, sometimes performing acrobatic figures (e.g.

Dolphins are social, living in pods (also called "schools") of up to a dozen individuals.

Because of their capacity for learning, dolphins have been employed by humans for any number of purposes. Such places may sometimes also provide an opportunity for humans to interact very closely with dolphins. Dolphin-human interaction is also employed in a curative sense at places where dolphins work with autistic or otherwise disabled human children. The military has employed dolphins for various purposes from finding mines to rescuing lost or trapped humans. Such military dolphins, however, drew scrutiny during the Vietnam War when rumors circulated that dolphins were being trained to kill Vietnamese skin divers.

In May 2005, researchers in Australia discovered a cultural aspect of dolphin behaviour: Some dolphins (Tursiops aduncus) teach their children to use tools.

Dolphins are one of the few animals other than humans known to mate for reasons other than reproduction. Sex does not appear to be consensual in all cases however, with male Bottlenose Dolphins even being known to molest dolphins of different species.

Feeding

Dolphins are predators, chasing their prey at high speed. In South Carolina, coastal Bottlenose Dolphins take this one step further with what has become known as mudding, where the fish are driven onto mud banks and retrieved from there.

Threats to dolphins

They are an endangered species because of big fishing nets, which catch dolphins as well as fish. Some dolphin species face an uncertain future, including pink dolphins, black dolphins, Amazon River dolphins, and the Ganges and Yangtze River dolphins, all of which are critically or seriously endangered. For example, only seventeen Yangtze River dolphins are known to exist.

Contamination of environment - the oceans, seas, and rivers - is an issue of concern, especially pesticides, heavy metals, plastics, and other industrial and agricultural pollutants that do not disintegrate rapidly in the environment are reducing dolphin populations, resulting in dolphins building unusually high levels of contaminants.

Various fishing methods, most notably purse seine fishing for tuna and the use of drift and gill nets, results in a large amounts of dolphins being killed inadvertently. In some parts of the world, such as Japan and the Faroe Islands, dolphins are actively hunted and killed, usually in harpoon or drive hunts.

Hybrid dolphins

See also: Wolphin

In 1933, three abnormal dolphins were beached off the Irish coast; these appeared to be hybrids between Risso's Dolphin and the Bottlenose Dolphin. In captivity, a Bottlenose Dolphin and a Rough-toothed Dolphin produced hybrid offspring. Normally, Spinner Dolphins have sometimes hybridised with Spotted Dolphins and Bottlenose Dolphins. Bands of males of one dolphin species often mate with lone female Spinners.

Dolphins in human culture

Dolphins have long played a role in human culture. Dolphins are common in Greek mythology and there are many coins from the time that feature a man or boy riding on the back of a dolphin. In Hindu mythology, the Ganges River Dolphin is associated with Ganga, the deity of the Ganges river.

In more recent times, the 1963 Flipper movie and the subsequent popular Flipper television series, contributed to the popularity of dolphins in Western society. Flipper, a Bottlenose Dolphin, understood English unusually well and was a marked hero. A bottlenose dolphin also played a prominent role in the 1990's science fiction television series seaQuest DSV in which the animal, named Darwin, could communicate with English speakers using a vocoder, a fictional invention that translated the clicks and whistles to English and back. The 1973 movie The Day of the Dolphin also has a dark role for dolphins, which are trained to perform an assassination.

The renewed popularity of dolphins in the 1960's resulted in the appearance of many dolphinariums around the world, which have made dolphins accessible to the public.

Dolphins are also common in contemporary literature, especially science fiction novels. In the second book of the Rifters trilogy, Maelstrom, by Peter Watts, enhanced Bottlenose Dolphins are used as underwater hunter-killers by a private military. An other military role for dolphins is found in William Gibson's short story Johnny Mnemonic, in which cyborg dolphins are used in war-time by the military to find submarines and, after the war, by a group of revolutionaries to decode encrypted information. In the book Startide Rising by author David Brin, a spaceship named Streaker is also manned by enhanced dolphins, whose intelligence matches that of humans. More humourus is The Hitchhiker's Guide to the Galaxy, in which dolphins are the second most intelligent creatures on Earth, after mice, and tried in vain to warn humans of the impending destruction of the planet. In the science fiction comic The Ballad of Halo Jones, dolphins are a respected species that are the best at piloting spacecraft, and are very peaceful and anti-war.

Dolphins also appear frequently in non-science fiction literature however. Fantasy author Ken Grimwood wrote dolphins into his 1995 novel Into the Deep about a marine biologist struggling to crack the code of dolphin intelligence, including entire chapters written from the viewpoint of his dolphin characters. In this book, humans and dolphins are capable of communicating via telepathy.

Occasionally, dolphins make an appearance in computer games. The games are named after their main character, Ecco, a young Bottlenose Dolphin.

Dolphins are also featured in several comic animated television series. In a Halloween episode of The Simpsons, dolphins reveal the ability to speak, walk on land, and their taste for humans while in a King of the Hill episode, Hank is molested by an aroused dolphin.

An American National Football League (NFL) team is named the Miami Dolphins. Their logo depicts an aqua-colored Bottlenose Dolphin wearing an American football helmet and jumping in front of a coral-colored sunburst.