The common ancestors of birds and mammals were very early (stem) reptiles, which almost certainly possessed three-chambered hearts (two atria, one ventricle). Birds and mammals, however, are alike in having four-chambered hearts (two atria, two ventricles). The four-chambered 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.

Homoplasy refers to the presence of similar characters in different species. These similar features are not shared with their common ancestor and therefore, are not the result of convergent evolution. Mammals and birds have four-chambered hearts which was not present in their common ancestors (reptiles).

Therefore, the four-chambered heart is a homoplastic feature that developed independently in mammals and birds to meet their higher demand for oxygen to maintain the constant body temperature. The four-chambered heart keeps the deoxygenated and oxygenated blood separate to efficiently supply the oxygen-rich blood to cells.