Question

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

Answer 1

Common fundamental features can be taken into account for classification into certain categories or sub-categories. For the common fundamental feature of all the Arthropods is joined legs for locomotion. Higher animals, like mammals too have joined legs but the difference is the absence/presence of muscles to facilitate articulation. Similarly, all birds have fore-limbs modified to assist in flying. This gives us one clue to categories a particular animal among Avis.

Answer 2

the animals cannot be classified into different groups,class etc if their common fundamental features are not taken into account .