Porpoises: Phocoenidae

Porpoises are mostly ocean-dwelling marine mammals, although some species can also live in freshwater rivers. They are often confused with dolphins. In casual conversation many people incorrectly use the terms dolphin and porpoise to mean the same thing. Both porpoises and dolphins came from a common ancestor, ancient relative, however they have been distinct families for about eleven million years.

Porpoises have a blunt snout, as opposed to the beak and elongated snout of dolphins. Their dorsal, back, fins are triangular. They have thick, stocky bodies that help them to conserve heat in cold waters. There are several differences between the skulls of porpoises and dolphins, but the most obvious is in the teeth. Porpoises have between sixty and 120 almost triangular, spade-shaped teeth, while dolphins have cone-shaped teeth. Most members of this family lack a melon. The melon is a fatty organ on the forehead. This gives their heads a tapered rather than a bulging look.

Porpoises range in weight from 90 to 485 pounds (40 to 220 kilograms) and in length from 4 to 7 feet (1.2 to 2.2 meters). The smallest porpoise is the vaquita (vah-KEE-tah), which lives in the Gulf of California in Mexico. Dall's porpoise and the spectacled porpoise are the two largest porpoises. In all species except the spectacled porpoise, females are larger than males.

Porpoises range in color from black to gray to tan. Generally, their backs are dark and their bellies are lighter. Some, such as the spectacled porpoise and Dall's porpoise, have quite distinctive black and white markings. Others, such as the finless porpoise, are a single dull color.