Why whales classified as mammals although they are aquatic?
The requirement (and actually the meaning of the word) for being mammal is “having mammal glands”, that means the female feed their young milk. Where they live, how they reproduce is irrelevant–there are mammals who lay eggs (the platypus, the spiny anteater), but they still produce milk. Whales produce milk to feed their young; tens of millions of years ago, their ancestors lived on land (do a seach on ambulocetus).
