Here's why:
* They breathe air: Whales have lungs and must come to the surface to breathe, unlike fish.
* They give birth to live young: Whales are not egg-laying, and their young are born alive.
* They nurse their young: Whales produce milk to feed their babies.
* They are warm-blooded: Whales maintain a constant body temperature, unlike reptiles who are cold-blooded.
While whales live in the ocean and share some similarities with fish, they are much more closely related to land mammals.