They vary in size from 1.2 metres (4 ft) and 40 kilograms (88 lb) (Maui's Dolphin),
up to 9.5 m (30 ft) and ten tonnes (the Orca or Killer Whale).
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 are considered to be amongst the most intelligent of animals and
their often friendly appearance and seemingly playful attitude have made
them popular in human culture.