A mammal is a warm-blooded animal whose young are born alive and fed with mother’s milk. Strangely enough, there are quite a few creatures who live in the sea who are mammals.

A zoologist groups these creatures under the name “Cetaceans.” They include the whales, the porpoises, and the dolphins. By studying their skeletons and other parts, we can determine that the ancestors of these animals lived on land in very ancient times.

When they began to live in the water, the form of their body gradually changed and became fishlike, because they had to live like fishes. The hair which used to cover their bodies disappeared and their skin became smooth. The hind legs they used to have disappeared, too, and they developed powerful flat tails. The forelimbs became paddles.

Fish have gills for breathing, but whales have lungs and breathe air. This is why they must come to the surface every half-hour or so and take in more air. At the moment they emerge from the water, the pent-up air from their lungs is released. It comes out through the nostrils at the top of the nose and not from the mouth. Whales can swim with their mouths open because their nostrils are connected directly with the windpipe. Therefore, when water enters their mouth, it doesn’t choke them.

We all know that the dinosaurs were huge creatures, but even the biggest dinosaur was smaller than certain types of whales. In fact, the blue rorqual whale, also called the “sulphur-bottom,” is probably the biggest animal that ever existed on this earth. Some of them are more than 30 meters long, while the biggest dinosaur we know of was only about 24 meters long. The average weight of one of these monsters is 68 tonnes. A new-born blue whale is bigger than a full-grown elephant! While its mother is nursing it during the first year, it reaches a length of about 18 meters.