An unusual species of mammals, whales are classified in the order Cetacea, the same order that includes dolphins and porpoises. Whales are warm blooded, breathe air and have lungs, bear live young and nurse them on milk. But unlike other mammals, they live completely in the water. That's why ancient civilizations believed whales were fish until the Greek philosopher Aristotle noted that both whales and dolphins breathed through blowholes and delivered live babies instead of laying eggs.

There are two suborders of whales that have evolved differently over time. Baleen whales (suborder Mysticeti) are named after the Norse word for "grooved," because the 10 species have large grooves or pleats on their throats and bellies. Whales in this suborder lack teeth and feed mostly on small fish and plankton. Yet even with this relatively small-sized diet, they can grow extremely large. The blue whale, the largest species...