Final answer:
Whales share common features with their closest relatives including mammary glands, the presence of hair or fur, and a similar bone structure in their flippers as compared to land mammals, signaling a common evolutionary ancestry.
Step-by-step explanation:
Whales and their closest relatives share several features, indicating a common ancestry with other mammals. The first feature is the presence of mammary glands, which all mammals have and use to feed their young. Secondly, they share the presence of hair or fur at some point in their life cycle. Although whales have very little hair, it is present in fetal whales. Lastly, whales have a similar bone structure in their flippers to the limbs of land mammals, which is an example of homologous structures indicating a shared evolutionary path. These characteristics highlight the transformation from land-dwelling ancestors to ocean-dwelling mammals, as seen in cetaceans.