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Animal Kingdom

Question
CBSEENBI11002541

Which one of the followings in birds, indicates their reptilian ancestry?

  • Scales on their hind limbs

  • Four chambered heart

  • Two special chambers crop and gizzard in their digestive tract

  • Eggs with a calcareous shell

Solution

D.

Eggs with a calcareous shell

Nearly a century ago, T H Huxley called birds ' glorified reptiles' thereby meaning that birds have evolved from some reptilian ancestor. Both birds and reptiles lay the same type of eggs, which are deposited outside water. Eggs are large and telolecithal.The ovum is surrounded by albumen, an egg membrane and a thick hard calcareous shell, which are all secreted by special glands located in the walls of the oviduct. 
Birds like mammals have a completely four-chambered heart with double circulation, in which there is no mixing of pure and impure blood., All birds have horny epidermal scales confined to the lower parts of their legs and feet, which are exactly like the epidermal scales of the reptiles. Besides birds are covered by feathers, which are homologous to the reptilian horny scales as they have a similar origin and develop from similar germ buds.