The porpoises are small cetaceans of the family Phocoenidae; they are related to whales and dolphins. They are distinct from dolphins, although the word "porpoise" has been used to refer to any small dolphin, especially by sailors and fishermen. The most obvious visible difference between the two groups is that porpoises have flattened, spade-shaped teeth distinct from the conical teeth of dolphins.
The name derives from French pourpois, originally from Medieval Latin porcopiscus (porcus pig + piscus fish).
Porpoises, divided into six species, live in all oceans, mostly near the shore. Probably best known is the Harbour Porpoise, which can be found across the Northern Hemisphere.Dolphins are larger and always have cone-shaped teeth,
usually have a beak and usually have a hooked or curved dorsal fin (some have no dorsal fin).
Porpoise always have spade-shaped teeth, never have a beak, and usually have a dorsal fin shaped like a triangle (some have no dorsal fin).Scientifically they are the same. A porpoise is just a type of dolphin. Hope this helped!