Wasn't that a common language thing before an actual taxonomy was developed? Like the word for creatures that fly was "bird," the word for things that live in the water and swim was "fish," etc? Like differentiating birds and bats requires a framework for understanding that one warm-blooded flying creature is more related to mice, dogs, people, etc (and understanding that all of these things are related) than to these other warm-blooded flying creatures that have no extant relatives that are wildly different from them, differentiating whales or dolphins from fish requires understanding that they breathe air and are related to non-bird warm-blooded land animals, etc.