Dolphins and porpoises belong to the suborder known as "Odonotoceti" - which literally means "toothed whale" although the number and size of teeth can vary greatly between species. A substantial number of "whales" also belong to this sub-order as they possess teeth as opposed to baleen.
Common characteristics of a toothed whale include: a single blowhole, an asymmetrical skull, three sternum bones and a fatty organ in the forehead called the ‘melon’ – used like a lens to focus sound-waves when using echolocation to target individual prey items. Apart from dolphins and porpoises, the suborder odontoceti contains several other members including the sperm whales, beluga whale or any member of the beaked whales - however as they're more commonly known by the term "whale". Find out the difference between whales, dolphins and porpoises.
With 36 species, this dolphin family contains the most diverse members of the cetacean world. The delphinids are known as the ‘marine dolphins’ (although of course there are some exceptions to the rule, with the freshwater populations of Orcaella bucking the trend), have a noticeable beak (with Orcaella again the exception), a large falcate, dorsal fin mid-way along their back (but not Lissodelphis) and conical teeth. Large group sizes and a complex social structure is a theme within the delphinids.
This is the porpoise family, containing seven species, each of which is relatively small and stocky. Each species has flattened spade-shaped teeth, either a short beak or no beak at all and in all except the 2 species of finless porpoise, a small triangular dorsal fin. The females of some species can also be larger than the males.