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

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 characteristic is considered, then this objective would not be achieved.

Using the common fundamental features helps in segregating the animals in different groups. Let us take the example of presence or absence of notochord. This feature helps us in grouping the animals among chordates and non-chordates. Similarly, two or three embryonic layers are taken for grouping the animals under diploblastic and triploblastic categories. Use of fundamental features in classification paves the way for further segregation of animals among different sub-groups.