The order Cetacea, that includes whales, dolphins, and porpoises is divided into two main groups: the toothed whales (Odontocetes) and the baleen or whalebone whales (Mysticetes). Toothed whales include dolphins, porpoises, as well as the large sperm and killer whales. Baleen whales include all of the largest whales; in fact the largest living animal on earth, the blue whale, is in this group.
Not all toothed whales have teeth visibly present as adults; some, like certain beaked whales, are “toothless” although teeth are present beneath the gums. The narwhals also are toothless except for the one large tusk of males. However, many Odontocetes have upwards of 300 conical or wedge-shaped teeth. These whales take large prey including fish, large invertebrates, and marine mammals. They also are different from baleen whales in that they are capable of echolocation, a method of sensing surrounding objects with pulses of high-frequency sound.
The baleen whales include the right whales, rorquals, humpacks, and gray whales. Baleen, known as whalebone, is actually made of keratin, material found in hair and fingernails. Baleen grows from the upper jaw in the huge mouths of these whales, in plates with fringes that act as a sieve to filter small schooling fish or zooplankton. Some mysticetes feed by skimming through schools of fish, others gulp huge amounts of water in distended throats and then strain the food through the baleen. Amazing when you think that the largest of animals feed on the tiniest of prey!