Are porpoises and dolphins different mammals?

The Northeastern Offshore Spotted Dolphin, shown here, has a falcate, or sickle-shaped dorsal fin and light spotting on the belly. read more

People use the terms dolphins, porpoises, and whales to describe marine mammals belonging to the order Cetacea (from the Greek work ketos, “large sea creature”), and often use them interchangeably. The orca, or killer whale, for example, is actually the largest member of the dolphin family. read more

Porpoises are part of the scientific family Phocoenidae, while dolphins are part of the Delphinidae family. When you concentrate on the differences at the family level, dolphins and porpoises can seem quite different. There are definite, yet subtle physical differences between the two aquatic mammals. read more

The dorsal fin, the one in the middle of the back, may be a key differentiator of the marine mammals, at least for sunbathers who may catch just a glimpse of the animal. Dolphins have a curved, or hooked, fin, while porpoises are equipped with a triangular one, NOAA says. read more