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The whale is the most specialized of all mammals on Earth. It is completely adapted to life in the water. Its body is streamlined and it has no hind limbs. The whale’s tail flukes are used for swimming and are not made of bone, but of a softer substance known as cartilage (your nose is made of cartilage). The whale’s front limbs have evolved into flippers which are used for steering. To maintain their warm body temperature in the often frigid water and to insulate them from the cold, whales have a layer of fat, called blubber, up to 20 inches thick.

Whales still have some similarities to land mammals. They have to come to the surface to breathe air. Their young are born alive after being carried by the mother for 12-18 months. The young whale (called a calf) suckles milk from the mother’s mammary glands, which are located inside her body.

There are two groups of whales. One group is known as odontoceti (o-dont-o-seat-ee), which means toothed whale, and includes the familiar bottlenose dolphin and orca. The other group is known as mystoceti (mist-o-seat-ee) or baleen (bay-leen) whales. Instead of teeth, this group of whales has fringed strainers hanging from their upper jaw. These strainers are called baleen. The baleen is used for catching and filtering out schools of fish and plankton from the water. Included in this group are blue and humpback whales. A baleen whale may have up to 400 baleen plates on each side of its upper jaw. The baleen is not a modified tooth; in fact it feels more like a fingernail.

Whales were not always found in the ocean. The story of their development began a long time ago. It’s rather strange that while all life on Earth started microscopically in the oceans and got progressively bigger, whales—the largest of all animals—developed through evolution from land mammals and only then entered the sea. Scientists have learned about the ancestors of whales by studying fossils that were found at the edge of ancient shallow seas. The earliest known ancestors of whales looked a lot like hippopotamuses! (For more on this, see National Geographic's site: http://magma.nationalgeographic.com/ngm/data/2001/11/01/html/ft_20011101.4.html )

From Ocean to Land and Back