If a phylogenetic analysis shows that an assemblage of species is closely related,but only one of the species has evolved drastically different morphology that is known to be extremely costly,then why might this one species have evolved such a distinct trait?

A) This organism mutated and differentiated quickly due to density-dependent selection.
B) This organism likely speciated and evolved in a community where predator mediated coexistence was favored.
C) Evolution is a mystery. Who knows?
D) This organism likely evolved in a much more harsh environment.