Dolphins, whales are mammals without legs

"If whales and dolphins are mammals and breathe air, why can't they come on land?" asked Rebecca Slawin, 11, of Gurnee, a soon-to-be 7th-grader at Viking School.

Dolphins and whales are a part of the order Cetacea. They are mammals, which means they are warm-blooded. Like horses, cows and people, they give birth to live babies, which they nurse. Most mammals have hair. Whales and dolphins have blubber instead that regulates body temperature in cold water. These mammals spend nearly their entire lives under water, surfacing only a few times each day to gulp air into their lungs. The rest of the time they remain in their underwater home.

Michael Henderson, paleontologist and curator of earth sciences at Rockford's Burpee Museum, said, "Whales and dolphins did have terrestrial ancestors in the early Tertiary Period about 60 million years ago. In the last couple of decades some remarkable early whales have been discovered in the Middle East and Egypt which document some of the early stages in the evolution of whales."

There's still lots to learn about Cetaceans. Fossils of whale teeth and bone fragments reveal prehistoric times with ancestors that date back millions of years. As seas expanded to cover much of the earth, scientists believe traces of hind legs vanished so Cetaceans would better adapt to a water life. Specialized organs developed that assist with echolocation and diving. Nearly 40 million years ago, some species developed baleen plates that act like nets to capture tiny plankton for nutrition.

Whale and dolphin evolution has made it impossible for these mammals to be at home on land. Ken Ramirez, vice president of animal collections and training at Chicago's Shedd Aquarium, said, "There are several reasons that they cannot come out on land. The most obvious is that they do not have feet to allow them to move around easily on land. Additionally, the thick blubber layer they have developed to keep them warm in the water would cause them to overheat if they lived on land."

Scientists speculate that the blue whale, the world's largest animal with the weight equivalent of 33 elephants, would need some mighty huge legs to keep it mobile if it were to live on land. Water's buoyancy can keep an extremely large animal sleek, speedy and always at the ready when it comes to grabbing a fish or plankton snack.

Henderson added, "Modern whales are extremely well adapted for life in the water, and consequently, a land existence is now impossible for them. The examples of beached and stranded whales which occasionally make it into the news are dramatic evidence that modern whales are totally dependent on water for their existence."