What is a dolphin?

There are about 80 species of whales, dolphins and porpoises known to exist in the world today. They all belong to the order of mammals known as cetaceans.

Cetaceans are divided into two suborders - the Mysticeti (or baleen whales) and the Odontoceti (or toothed whales). These suborders, and the smaller subgroups beneath them, are based on a logical, well-defined system for classifying animals by common characteristics. However, the popular names given to cetaceans are often less consistent and more confusing.

For instance, some small cetaceans are called whales. Most of the mysticetes are referred to as great whales, as is the sperm whale (an odontocete), because of their size.

Both the killer whale and the pilot whale are members of the family Delphinidae, which includes all oceanic and some coastal and river dolphins. The narwhal belongs to a different family - the monodontidae, which also includes the beluga (or white whale). However both of these can also be referred to as dolphins, as they belong to the superfamily Delphinoidea.

Although many people use dolphin and porpoise interc hangably, strictly speaking "porpoise" refers only to the six members of the family Phocoenidea which are all small and robust species.

For the most part, almost any toothed whale could be called a dolphin without being too far off.

Their intelligence

Because dolphins are highly social and vocalize among themselves with a wide range of sounds, it has been conjectured that they might possess an almost humanlike intelligence. In the 1950s and '60s the American neurologist John Lilly conducted well-publicized experiments based on this concept, in which he attempted to communicate with dolphins in their own "language," but other scientists have rejected his work as poorly documented and lacking scientific validity. Most researchers agree that dolphins exhibit a level of ntelligence greater than that of dogs and even comparable to that of some primates--but not human beings. Research into dolphin intelligence continues at centers such as Hawaii's Kewalo Basin Marine Mammal Laboratory.