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

Explanation

For the classification of living organisms common fundamental characteristics are considered. If we consider specific characteristics, then each organism will be placed in a separate group and the entire objective of classification would not be achieved. Classification of animals is also important in comparing different organisms and judging their individual evolutionary significance. If only a single characteristics is considered, then this objective would not be achieved.