shared derived characteristic definition
Aspect of two species that are equivalent as a consequence of, that is, aspects that are homologous. Shared characters can either either be unique to a taxon (and therefore represent a shared derived character) or instead may be shared with other, related taxa (and therefore represent a shared ancestral character). In either case, shared characters are. The distinction is in how far back one has to go to reach the ancestor in which the shared character first arose. Only if one need not leave a specific clade to reach that ancestor is the character described as a shared derived character.