Homology that is unique to a specific taxon.

It is important to realize that a shared derived character is unique to a taxon not arbitrarily but instead because a taxon, as a specific clade, has been defined in terms of the shared derived character. See by contrast shared ancestral character or simply shared character.

The shared derived character is shared specifically with a common ancestor to other species that also share that character but not to ancestor of that specific common ancestor. See equivalently .

, for example, are defined by their and production of milk, both of which are unique to that taxon.