The common ancestors of birds and mammals were very early (stem) reptiles, whichalmost certainly possessed three­chambered hearts (two atria, one ventricle). birds andmammals, however, are alike in having four­chambered hearts (two atria, two ventricles).the four­chambered hearts of birds and mammals are best described as
a) structural homologies.
b) vestiges.
c) homoplasies.
d) the result of shared ancestry.
e) molecular homologies.