Dolphin - Intelligent Mammal

Dolphins are a widely distributed and diverse group of fully aquaticmarine mammals. They are an informal grouping within the orderCetacea, excludingwhales andporpoises, so to zoologists the grouping isparaphyletic. The dolphins comprise the extant familiesDelphinidae (the oceanic dolphins),Platanistidae(the Indian river dolphins),Iniidae (the new world river dolphins), andPontoporiidae (the brackish dolphins). There are 40 extant species of dolphins. Dolphins, alongside othercetaceans, belong to the clade Cetartiodactyla with even-toed ungulates, and their closest living relatives are the hippopotamuses, having diverged about 40 million years ago.

Dolphins range in size from the 1.7-metre-long (5.6 ft) long and 50 kg (110 lb) Maui's dolphinto the 9.5 m (31 ft) and 10 t (11 short tons) killer whale. Though not quite as flexible as seals, some dolphins can travel at 55.5 kilometres per hour (34.5 mph).  They have well-developed hearing—their hearing, which is adapted for both air and water, is so well developed that some can survive even if they are blind. Although dolphins are widespread, most species prefer the warmer waters of the tropic zones, but some, like the right whale dolphin, prefer colder climates. Dolphins feed largely on fish and squid, but a few, like the killer whale, feed on large mammals, like seals. Dolphins are sometimes hunted in places like Japan, in an activity known as dolphin drive hunting. Besides drive hunting, they also face threats from bycatch, habitat loss, and marine pollution.