Final answer:
Whales that evolved after Ambulocetus have vestigial hindlimbs as evidence of their land-dwelling ancestors. Their transition into aquatic life is marked by adaptations like the development of flippers, which are homologous structures indicative of shared evolutionary history with other vertebrates.
Step-by-step explanation:
Whales that evolved after Ambulocetus display a common characteristic of having vestigial hindlimbs. The presence of these rudimentary limbs provides substantial evidence that modern whales descended from terrestrial ancestors and shares a common ancestry with even-toed ungulates such as hippos, cows, and camels. This transition from land to sea over evolutionary time scales is evident in the fossil records, like that of Pakicetus and Rodhocetus, where changes in the body structure supporting aquatic life can be observed. Though modern whales lack external hindlimbs, the presence of vestigial pelvis and femur bones in some species points to the terrestrial lineage of these marine mammals. The phylogenetic relationship between different species shows how certain adaptations are derived or lost due to evolution. For example, the evolution of flippers in whales from forelimbs is an adaptive characteristic unique to their water environment but also demonstrates their common descent with other mammals. In the case of cetaceans, their flippers are a homologous feature indicating a shared evolutionary history with other vertebrates, whereas the analogies with fish are due to convergent evolution displaying similar body shapes to adapt to similar environments even though they have different evolutionary histories.