海豚(eng)簡介

Dolphins are highly intelligent aquatic mammals that are closely related to whales and porpoises. The name is from Ancient Greek δελφίς delphis meaning "with a womb", viz. "a 'fish' with a womb". A group of dolphins can be called a "school" or a "pod".

The word is used in a few different ways. 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.
In this article, the second definition is used. 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. They vary in size from 1.2 m (4 ft) and 40 kg (88 lb) (Maui's Dolphin), up to 9.5 m (30 ft) and ten tonnes (the Orca). However, the average length for most North American species is 13.89 feet (4.23 m) in length. Most species weigh about 50 to 200 kg (110 to 440 lb). They are found worldwide, mostly in the shallower seas of the continental shelves, and are carnivores, mostly eating fish and squid. The family Delphinidae is the largest in the Cetacea, and relatively recent: dolphins evolved about ten million years ago, during the Miocene.
Dolphins, along with whales and porpoises, are thought to be descendants of terrestrial mammals, most likely of the Artiodactyl order. Modern dolphin skeletons have two small rod shaped pelvic bones thought to be vestigial hind legs. They entered the water roughly fifty million years ago.

Dolphins have a fusiform body, adapted for fast swimming. The head contains the melon, a round organ used for echolocation. In many species, the jaws are elongated, forming a distinct beak; for some species like the Bottlenose, there is a curved mouth that looks like a fixed smile. Teeth can be very numerous (up to two hundred and fifty) in several species. The dolphin brain is large and has a highly structured cortex, which often is referred to in discussions about their advanced intelligence. 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.[1] This theory has not found widespread acceptance. Their teeth are arranged in a way that works as an array or antenna focusing the incoming sound, making it easier for them to pinpoint the exact location of an object. The basic coloration patterns are shades of gray with a light underside and a distinct dark cape on the back. It is often combined with lines and patches of different hue and contrast. See individual species articles for details.
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. Furthermore, the difficulty and expense of doing experimental work with large aquatics means that some tests that could meaningfully be done still have not been carried out, or have been carried out with inadequate sample size and methodology. See the "cetacean intelligence" article for more details.

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dolphin



Bottle-nosed dolphins (Tursiops truncatus) (credit: Courtesy of the Miami Seaquarium)One of a large group of small, gregarious, streamlined whales or one of two species of oceanic sport and food fishes. Mammalian dolphins are small toothed whales, usually with a well-defined, beaklike snout. (They are sometimes called porpoises, but that name is properly reserved for a blunt-snouted whale family.) The common dolphin (Delphinus delphis) and the bottlenose dolphin, both of the family Delphinidae, are found widely in warm temperate seas, though some inhabit tropical rivers. Most of the 32 delphinid species are marine; gray, blackish or brown above and pale below; and about 3–13 ft (1–4 m) long. River dolphins (family Platanistidae; five species) live mainly in fresh water in South America and Asia. One of the two fish species, Coryphaena hippuras (family Coryphaenidae), also called mahimahi and dorado, is a popular fish of tropical and temperate waters worldwide. The pompano dolphin (C. equiselis) is similar. See also killer whale.