If you consider that, all whales, dolphins and porpoises are really whales. However, these terms can also be used as a way to distinguish size among species, with cetaceans longer than about 9 feet considered whales, and those less than 9 feet considered dolphins and porpoises.
Within the dolphins and porpoises, there is a wide range in size, from the orca (killer whale), which can reach lengths up to about 32 feet, to the Hector’s dolphin, which can be less than 4 feet long.
Difference Between Dolphins and Porpoises:
While dolphins and porpoises are very similar and people often use the term interchangeably, scientists generally agree that there are four major differences between dolphins and porpoises:
- Dolphins have cone-shaped teeth while porpoises have flat or spade-shaped teeth.
- Dolphins usually have a pronounced “beak,” while porpoises do not have a beak.
- Dolphins generally have a very curved or hooked dorsal fin, while porpoises have a triangular dorsal fin.
- Porpoises are generally smaller than dolphins.
To get even more specific, the term porpoise should also refer only to the seven species that are in the family Phocoenidae (harbor porpoise, vaquita, spectacled porpoise, Burmeister’s porpoise, Indo-Pacific finless porpoise, narrow-ridged finless porpoise and < href="http://marinelife.about.com/od/Toothed-Whale-Profiles/p/Dalls-Porpoise.htm">Dall’s porpoise.)
- American Cetacean Society. 2004. ACS Cetacean Curriculum (Online), American Cetacean Society. Accessed October 15, 2008.
- Waller, Geoffrey, ed. SeaLife: A Complete Guide to the Marine Environment. Smithsonian Institution Press. Washington, D.C. 1996.