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Dolphins are certain
aquatic mammals related to whales and porpoises. The name is from
Ancient Greek delphis meaning "with a womb", viz. "a
'fish' with a womb". 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 Platanistoidae (oceanic and river
dolphins), any member of the suborder Odontoceti (toothed whales;
these include the above families and some others), laypeople often
use the term synonymously with Bottlenose Dolphin, the most common
and familiar species of dolphin.
In this article, the second definition is used.
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Porpoises (suborder
Odontoceti, family Phocoenidae) are thus not dolphins in our sense.
Orcas and some related species belong to the Delphinidae family
and therefore qualify as dolphins, even though they are called
whales in common language. There are almost 40 species of dolphin
in 17 genera. They vary in size from 1.2 metres and 40 kg (Heaviside's
Dolphin), up to 9.5 metres and 10 tonnes (the Orca). Most species
weigh between about 50 and about 200 kg. They are found worldwide,
mostly in the shallower seas of the continental shelves, and all
are carnivores, mostly taking fish and squid. The family Delphinidae
is the largest in the Cetacea, and relatively recent: dolphins
evolved about 10 million years ago, during the Miocene.
Above Images Come From The National Undersea Research
Program
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