What are the difficulties that you would face in classification of animals, if common fundamental features are not taken into account?

Explanation

The art of identifying distinctions among organisms and placing them into groups is called classification. It reflects their most significant features and relationship. Classification of any organism including animal requires the knowladge of comparative anatomy, comparative ecology, comparative physiology and comparative biochemistry. We need all fundamental characteristics for the classification of animal. But if we ignore the fundamental characters than following difficulties we face in classifying animals :
(i)Classification system will not be uniform.
(ii)Distantly related group are placed together while closely related groups gets separated from each other.
(iii)It becomes difficult to place animal into the given group in a system of classification.
(iv)Classification will not become universal. It varies from time to time and place to place.
(v)Examples of adaptive divergence, vestigial organs, convergent evolution etc provide hinderance in classification of animal.