Synapomorphies at different levels

Synapomorphies at different levels help us resolve the entire phylogeny. The first character (A or B) resolves the polytomy indicated by the upper arrow. From the outgroups, we see the polarity of the trait: A is ancestral; B is derived. As a result, we conclude that two species with the B character are sister groups. The outgroups reveal the polarity of the second character. C is the ancestral trait; D is derived. This resolves the polytomy indicated by the lower arrow. The two clades with the D character are sister groups.