What is the difference between a dolphin and a porpoise?

Answer 1

Both names are used for several different species of toothed whales (odontocete cetaceans).
"Dolphin" is used for members of the family Delphinidae, while "porpoise" is especially used for the species of genus Phocoena (which belong to a different family, Phocoenidae).
Porpoises have blunt snouts, while dolphins have the well-known long "beaks".
This is a porpoise (sensu stricto):
http://www.swisscetaceansociety.org/glossaire/images/Phocoena%20phocoena.jpg

And this is a dolphin:
http://www.swisscetaceansociety.org/glossaire/images/Delphinus%20delphis.jpg

However, many people use the word "porpoise" for almost any dolphin-like creature, and it's not easy to find any difference between this and "dolphin" when this second meaning is used.

Answer 2

Porpoises have flattened, spade-shaped teeth distinct from the conical teeth of dolphins. Porpoises tend to be smaller but stouter than dolphins. They have small, rounded heads and blunt jaws instead of beaks. While dolphins have a round, bulbous "melon", porpoises do not. Their teeth are spade-shaped, whereas dolphins have conical teeth. In addition, a porpoise's dorsal fin is generally triangular, rather than curved like that of many dolphins and large whales. Some species have small bumps, known as tubercles, on the leading edge of the dorsal fin.

Answer 3

I always thought that a porpoise is more seal-like, with one of those big "unicorn" noses.
But it's actually pretty similair to a dolphin. Just go to Google images and see the similarity.

Answer 4

According to my dictionary, the dophin if of the porpoise family. A kind of cousin of the whales.

Answer 5

Watch that one scene in Ace Ventura. He'll tell you.