It was present in the ancestral vertebrate, and though different vertebrates have evolved differently shaped tails, they are all evolved from the common ancestral tail. The PRESENCE of the tail is primitive. 1  A derived character is one that is relatively modified from its original, ancestral form. a synapomorphy is a shared, derived character. 2  The more recently two species diverged from a common ancestor, the more synapomorphies they will share. 3  Unique synapomorphies found only in a single group provide strong evidence for the common ancestry of members of that group.