Unlike the whales of our oceans, whale sharks are not mammals. Instead whale sharks belong to a group of fish known as cartilaginous fish and is not a mammal. It just so happens that the blue whale, which is a mammal, is the largest animal that’s ever lived on planet earth. Whereas the whale shark is the largest species of any fish. The Guinness Book of Records whale shark was 12.65 metres (42.5 feet) long.