Dolphins are marine mammals that are closely related to whales
and porpoises. There are almost forty species of dolphin in
seventeen genera. Dolphins are often regarded as one of Earth's
most intelligent animals, though it is hard to say just how
intelligent. Comparing species' relative intelligence is complicated
by differences in sensory apparatus, response modes, and nature
of cognition. Furthermore, the difficulty and expense of experimental
work with large aquatic animals has so far prevented some
tests and limited sample size and rigor in others. Compared
to many other species however, dolphin behavior has been studied
extensively, both in captivity and in the wild.
Dolphins are social, living in pods of up to a dozen individuals.
In places with a high abundance of food, pods can merge temporarily,
forming a superpod; such groupings may exceed 1,000 dolphins.