A porpoise is a porpoise. It's not a fish and it's not a dolphin. They are warm-blooded mammals that breathe air using lungs and the young suckle milk from their mothers. A porpoise is actually like a dolphin's cousin, similar but still two worlds a part like any extended family.

Porpoises belong to the Family Phocoenidae while dolphins belong to Delphinidae, but they both belong to the order cetacean along with whales. And like all those crazy cetacean creatures, porpoises use echolocation, which evolution kindly has provided. Unlike dolphins who live by the equator, porpoises live all over but namely in the northern hemisphere. Porpoises don't have extended snouts or beaks like dolphins, or big bulbous foreheads and large flippers. Their dorsal fins are smaller and triangular, their teeth are a spade-shaped and their flutes are notched. While dolphins love to bow-ride and perform acrobatic leaps out of the water, also known as breaching, porpoises rarely do.

The Harbor Porpoise, or common porpoise resembles a dolphin but makes a distinct puffing sound when they breathe. This is often the only way to locate one in the vicinity. Like most species of porpoises they are timid and wary of boats. Making this water-bound mammal rarely observed in the wild. While the Dall's porpoise looks a lot like a killer whale, it's the fastest of all the small cetaceans. It can reach speeds of 30 knots creating a wake known as a rooster tail that allows the Dall's porpoise a hollow area for breathing air while keeping the body slightly submerged under the water's surface.

Within the Phocoenidae family there are six species of porpoises; Harbor Porpoise, Dall's Porpoise, Spectacled Porpoise, Burmeister's Porpoise, Finless Porpoise and finally Vaquita.



http://www.acsonline.org/factpack/HarborPorpoise.htm
http://www.theporpoisepage.com/