Direct Answer
The phrase "lion is a dog" is biologically incorrect; lions are not dogs. Both are mammals in the order Carnivora and share a distant common ancestor, but they belong to different families. Lions (Panthera leo) are part of the cat family (Felidae), while domestic dogs (Canis lupus familiaris) belong to the dog family (Canidae). This article explains their relationship, key differences, and why the confusion arises.
