In A Nutshell
Dolphins and porpoises both belong to the Cetacea order of mammals, but they do belong to different families. In spite of a general similarity in shape and appearance, dolphins and porpoises have distinctly different features, such as the shapes of their fins and heads. They also vocalize in a very different manner, and demonstrate very different behavior patterns.
The Whole Bushel
Dolphins belong to the Delphinidae family, while porpoises belong to the Phocoenidae family. Dolphin species are much more numerous, with at least 32 marine dolphin species to date and more being discovered. (As recently as October 2013, a new species of humpback dolphin was discovered off the coast of Australia, similar in appearance to other species but with drastically different DNA.) There are also five species of river dolphins, but there are only six different species of porpoise.
One of the most major differences between the two is also the least noticeable—their teeth. The teeth of a dolphin are conical, while the teeth of a porpoise are flatter and spade-shaped. Their faces also have a different shape, with dolphins tending to have a longer, narrower beak than porpoises, most of whom have a shorter, more squat face.
Most dolphins and porpoises can also be differentiated by their dorsal fin, although the difference in shapes can be less pronounced in some species. On the whole, the dorsal fin of a porpoise is triangular, while the dorsal fin of a dolphin has a curve. The body of a dolphin tends to be longer and leaner than that of a porpoise, though there are some species of both that bend this rule a bit.
Both groups are highly intelligent and have a complex communication system. The difference is that we can hear dolphins. Dolphins communicate in a wide variety of clicks and whistles that we are able to hear, record, and easily study. Porpoises, on the other hand, have a more limited range of vocalizations that the human ear can’t detect. Their clicks and whistles are on a much higher frequency than we are capable of hearing, and on a much more narrow band of frequencies than dolphin communication.
Behaviorally, dolphins tend to be a lot more playful than porpoises. Notorious for their ability to jump completely out of the water, dolphins can be seen doing this frequently. Porpoises do not show this behavior.
And perhaps the most disturbing difference is that dolphins will kill porpoises with shocking brutality. The two coexist in coastal regions around the world, and studies have shown that the sharing of waters is rarely peaceful, with fights often strongly favoring the bigger, bolder dolphins. For several decades, biologists have been studying groups of dolphins and porpoises that share waters off the coast of Virginia, the east coast of Scotland and the coast of Wales. Mutilated bodies of porpoises have long been washing up on all shores, showing signs of extreme blunt force trauma and the teeth marks of dolphins. Dolphins have since been caught on video viciously attacking their shy cousins, leaving scientists wondering exactly why porpoises are such easy and frequent targets for dolphins. Even those who share the same bays tend to alternate occupying it during the daytime or nighttime, and food doesn’t seem to be a point of contention.
While the idea of dolphins as killers might seem a little bizarre, the largest species of dolphin has it right in its name—the killer “whale” is actually a dolphin.
Show Me The Proof
NOAA: Dolphins and porpoises differ in their faces, fins, and body shapes
BBC: New species of dolphin identified
Telegraph: Killer dolphins baffle marine experts
The Guardian: Dolphins bully porpoises, researcher discovers
