Question

Sol.(d) [Key Concept: Birds' Reptilian Ancestry — Scales & Shelled Eggs] Both scales on their hind limbs and eggs with calcareous shells indicate birds' reptilian ancestry. These are vestigial/ancestral characters retained from their reptilian ancestors. The four-chambered heart evolved independently in birds and mammals. Archaeopteryx (the transitional fossil between reptiles and birds) had reptilian features like teeth and clawed wings.