Here's why:
* Different Orders: Dolphins belong to the order Cetacea, which includes whales and porpoises. Cows, on the other hand, are part of the order Artiodactyla, which includes other even-toed ungulates like pigs, hippos, and deer.
* Evolutionary History: Dolphins evolved from land mammals millions of years ago, while cows evolved from a separate line of land mammals.
* Physical Differences: Dolphins are marine mammals with fins and a streamlined body for swimming. Cows are terrestrial mammals with four legs and hooves.
So, while both dolphins and cows are mammals, they are very distantly related and belong to completely different branches of the mammal family tree.