In comparison to dolphins, porpoises are very small. Porpoises seldom exceed 7 feet in length, whereas many dolphins can exceed 10 feet in length. Porpoises are also more robust than dolphins. Dolphins have a lean sleek body, whereas porpoises often appear chubby. The dorsal fin of the dolphin is shaped in a wave.
Porpoises lack a rostrum or a beak.
This rostrum is very prominent in dolphins. Many porpoises do not live past their mid-teens. Porpoises have an intensive reproduction schedule that may play a role in their lack of longevitiy. A porpoise can become pregnant each year, give birth, and then it can become pregnant again five or six weeks later, so it can be nursing and pregnant at the same time. This can also happen in dolphins, but dolphins are larger in size and it seems their body is suited for handling such occurences, and anyhow it is less common.