Cetaceans

Although they live in the water, whales, dolphins, and porpoises are mammals. Like other mammals, they cannot breathe underwater, but must come to the surface for air. They breathe through a blowhole, or nostril, on the top of the head. Babies are born underwater and must be pushed to the surface by the mother so they can take their first breath.

Whales and dolphins also look different from many other mammals because they don't have fur. However, they do have a sparse covering of hair.

Their circulatory and respiratory systems have adapted to living in water. Whales and dolphins can dive deeply on a single breath. Whales and dolphins also have highly developed brains and are considered to be very intelligent.

All dolphins and some whales can use echolocation to find food and "see" whatever is around them. They make loud clicking and squeaking sounds that bounce off objects and echo back to them, enabling them to identify nearby objects and sources of food.