Which one of the following in birds indicates their reptilian ancestry?
- Two special chambers crop and gizzard in their digestive tract
- Eggs with a calcareous shell
- Scales on their hind limbs
- Four-chambered heart
Answer
(3) Scales on their hind limbs
Solution
As per NCERT (class Aves), the forelimbs of birds are modified into wings and the hind limbs generally have scales and are modified for walking, swimming or clasping the tree branches.
∵ Epidermal scales are the characteristic body covering of reptiles, the scales on the hind limbs of birds are a reptilian character retained by them,
∴ scales on the hind limbs indicate the reptilian ancestry of birds.
⇒ Crop and gizzard, calcareous egg shell and the completely four-chambered heart (with only the right aortic arch) are features of birds themselves.
Answer: (3)