The Common Ancestors of Birds and Mammals Were Very Early

Multiple Choice

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.