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

The circulatory and respiratory systems have adapted to living in water. Whales and dolphins can dive deep in the water on a single breath.

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