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) structural analogies
D) the result of shared ancestry

Question

Quizplus · Accepted Answer

The four-chambered hearts of birds and mammals are not due to shared ancestry, but rather have evolved independently. Therefore, they are not structural homologies or vestiges. They are best described as structural analogies, which are similar structures that have evolved independently in different lineages.

The Common Ancestors of Birds and Mammals Were Very Early