While both cats and whales are mammals, they are actually quite distantly related. Whales are more closely related to hippos than they are to cats.
Here's a simplified breakdown:
* Cats belong to the order Carnivora, which includes dogs, bears, and seals.
* Whales belong to the order Cetacea, which includes dolphins and porpoises.
* Hippos belong to the order Artiodactyla, which includes cows, pigs, and deer.
Evolutionarily, whales and hippos share a common ancestor that lived around 50 million years ago. Cats and whales share a common ancestor that lived much further back in time.