There are five animals A, B, C, D and E. The animal A uses its modified forelimbs for flying. The animal Buses its forelimbs for running whereas the animal C uses its forelimbs for grasping. The animal D can live on land as well as in water and uses its forelimbs to prop up the front end of its body when at rest. The animal E which respires by using spiracles and tracheae uses wings for flying but its wings are analogous to the modified forelimbs of animal A.
What does the existence of homologous organs in animals A, B, C and D tell us about their ancestors?