A trait shared by at least two and perhaps more taxa and
devolving on common ancestry is synapomorphy. A homologous trait is
quite similar. The forelimbs of all tetrapods are devolved from
common ancestry and would be traits shared by many taxa and
homologous traits. Cladists use the word synapomorphy more to show
closer relationships. Pliesiomorphy is the word cladists use to
show more ancient relationships.