LIFE SCIENCE

Detailed explanation-1: -Their land-dwelling ancestors lived about 50 million years ago. Meet Pakicetus, a goat-sized, four-legged creature that scientists recognise as one of the first cetaceans (the group of marine animals that includes dolphins and whales).

Detailed explanation-2: -Their ancestor is most likely an ancient artiodactyl, i.e. a four-legged, even-toed hoofed (ungulate) land mammal, adapted for running. Cetaceans thus have a common ancestor with modern-day artiodactyls such as the cow, the pig, the camel, the giraffe and the hippopotamus.

Detailed explanation-3: -The similar bone arrangement of the human, bird, and whale forelimb is a structural homology. Structural homologies indicate a shared common ancestor.