Why are whales and dolphins called mammals although they look like fish?

Whales and dolphins are called mammals, even though they look like fish, because they share key characteristics with other mammals, not fish:

* Give birth to live young: Unlike fish that lay eggs, whales and dolphins give birth to live young.

* Nurse their young with milk: They have mammary glands and produce milk to nourish their offspring.

* Breathe air: Whales and dolphins have lungs and must come to the surface to breathe air. Fish have gills and breathe underwater.

* Warm-blooded: They maintain a constant body temperature, unlike cold-blooded fish.

* Have hair (or fur): While some whales have very little hair, all whales and dolphins have hair at some point in their lives, even if it's just a few bristles.

Evolutionary History:

Whales and dolphins evolved from land mammals millions of years ago. They adapted to life in the ocean, evolving streamlined bodies and flippers for swimming. But their internal anatomy, including their respiratory system, circulatory system, and reproductive system, still reflects their mammalian ancestry.

So, while whales and dolphins have adapted to an aquatic lifestyle, they are still fundamentally mammals.