海豚 Dolphins

Dolphins are marine¹ mammals closely related to whales and porpoises². The name is originally from Greek (delphus), meaning womb. The animal's name can therefore be interpreted as meaning a fish with a womb. Along with whales and porpoises, dolphins are descendants of terrestrial mammals. There are almost forty species of dolphin and are found worldwide. They are carnivores, eating mostly fish and squid. Dolphins are members of the family Delphinidae which evolved relatively³ recently, about ten million years ago.

 

Doplhins' senses are very developed. Most dolphins have acute eyesight, both in and out of the water, and they can hear frequencies ten times or more above the upper limit of adult human hearing. Hearing is also used for echolocation, which all dolphins have. Dolphin teeth are believed to function as antennae⁴ to receive incoming sound and to pinpoint⁵ the exact location of an object. Beyond locating an object, echolocation also provides the animal with an idea on the object's shape and size, though how exactly this works is not yet understood. The dolphin's sense of touch is also well-developed, with free nerve endings densely⁶ packed in the skin, especially around the snout, pectoral fins⁷ and genital area. However, dolphins lack an olfactory⁸ nerve and lobes⁹, and thus are believed to have no sense of smell. They do have a sense of taste and show preferences for certain kinds of fish.

 

Dolphins are capable of making a broad range of sounds using nasal airsacs located just below the blowhole. Individual dolphins communicate using a variety of clicks, whistle-like sounds and other vocalizations. The clicks are directional and are for echolocation, often occurring in a short series called a click train. The click rate increases when approaching an object of interest. Dolphin echolocation clicks are amongst the loudest sounds made by marine animals.

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