A dolphin's slimmer body, beak-like nose and curved fins distinguish it from the porpoise's stout build, rounded face and triangular fins, according to the National Ocean Service. Although they are different species, dolphins and porpoises both belong to order Cetacea. Approximately 32 dolphin species have been discovered, while only six known porpoise species exist.
Dolphins are in the taxonomical family Delphinidae, while porpoises are in the Phocoenidae family. They both classify as "toothed whales," but a porpoise's flatter, rounded teeth differ from the pointier, conical shape of dolphin teeth. Porpoises have an average life span of 15 to 20 years, while dolphins can live more than 50 years, Wonderopolis states. Porpoises reproduce at a faster rate, which scientists believe contributes to their shorter lives.
Both species use echolocation to communicate underwater, but dolphins also use their blowholes to make whistling sounds. Porpoises and dolphins are highly intelligent and possess a special structure, known as a melon, in their heads to transmit sonar waves, the National Ocean Service states.
Dolphins are a popular attraction for humans because their "chatty" behavior makes them appear playful and sociable. In contrast, porpoises only produce sounds that aren't audible to the human ear, Wonderopolis states. Porpoises are more timid towards humans. They travel in small groups of two to four, known as pods, and rarely approach ocean vessels. Dolphins live in large groups and comfortably interact with humans in captivity and in open water.