Tim Zwit, age 13, of Indianapolis, Indiana, for his question:
How do porpoises and dolphins differ?
Both these charming creatures are seagoing mammals and both belong to the whale order, Cetacea. This makes them small cousins of the giant whales, the largest animals that ever lived on the planet Earth. In this large order of fabulous animals, some scientists award the dolphins a family of their own. And because of marked differences, the porpoises may be placed in a different cetacean family.
We cannot depend on their everyday names, for the so called performing porpoise at an aquarium is most likely a genuine dolphin. What's more, the common porpoise that frolics off our shores is called the blue nosed dolphin on the other side of the Atlantic. However, with a pair of field glasses and a few reminders, we can tell whether dolphins or porpoises are romping through the ocean waves.
The average porpoise has a chunky body about six feet long. He has a blunt round nose and broad, rounded flippers. The back fin that often pokes above the waves is blunt and rather squarish. His various relatives range from tropical shores far up to the Arctic and southward to the tip of South America.
The average dolphin is much larger and more streamlined. His elegant flippers are gracefully curved and so is the elegant fin on his back. Instead of a blunt round nose, he has a long tapering snout ¬somewhat like a beak. If you don't mind looking inside their big mouths, the teeth also may tell you which is which.
The common harbor porpoise has 27 wedge shaped teeth on each side of his jaws, top and bottom. This gives him a full set of 108 fine teeth. Dolphins have fewer teeth and some have none in the upper jaw. But this tooth examination is not really necessary, because the bigger dolphin's long tapering snout always gives him away. The 28 foot pilot whale is a dolphin, and though his beak is not outstanding, his big bulging forehead gives him away.
The largest dolphin is the so called killer whale, a handsome performer at large aquariums. He gets to be 30 feet long and his glistening black skin is marked with eye catching patches of snowy white. In the sea, this global traveler is famous for his famished appetite. His huge menu includes seals and walruses, even polar bears and larger whales.
The 18 foot false killer whale feeds mostly on cuttlefish and so do several other dolphins, though the eight foot common dolphin enjoys a fishy menu, including herring and pilchard. The common six foot porpoise crunches crustaceans and feasts on fish and cuttlefish.
Some of the larger dolphins lead rather solitary lives. But the common dolphins and the porpoises prefer to share life with groups of friends and relatives. These are the cetaceans that frolic in our offshore waters and of the two; the dolphins are larger and more graceful.