Why are dolphins not fish but mammals?
Dolphins cannot breathe in water using gills as fish can, do not have scales, and are not cold-blooded. Dolphins are mammals that returned to the sea millions of years ago. Being a mammal means that: they breathe air (and do not have gills like fish);
Why whale and dolphins are mammals?
Whales are mammals which means that, like humans and other land mammals, they have three inner ear bones and hair, they breathe air, and the females produce milk through mammary glands and suckle their young.
Is whale mammal or fish?
Whales are a widely distributed and diverse group of fully aquatic placental marine mammals. As an informal and colloquial grouping, they correspond to large members of the infraorder Cetacea, i.e. all cetaceans apart from dolphins and porpoises.