Its according to their organs.. where the my come from.. where they inhabit..what the eat.. how they look like..
take for example: reptiles.. they are classified as reptiles cause.. they are the only types of animals who have hard scaled skin not like fish..
The answer is ectopic pregnancy..this is the answer..
The whale still has traces of a hip and pelvis bones in the back of his body witch scientist think they used to walk on land
