Final answer:
Homologous and vestigial structures both indicate common ancestry. Homologous structures are inherited and adapted for different purposes, while vestigial structures have reduced functions. The limbs of mammals serve as an example of homologous structures and the hind leg bones in whales exemplify vestigial structures.
Step-by-step explanation:
The structures that share a common ancestry are homologous structures. Homologous structures are similar in different organisms because they were inherited from a common ancestor. These structures may have undergone evolutionary changes and thus may not necessarily have the same function in their respective species. Examples of homologous structures include the limbs of various mammals like bats, lions, whales, and humans, all of which descended from a common ancestor but have adapted these limbs for different purposes such as walking, running, swimming, or flying.
In contrast, vestigial structures are also evidence of common ancestry but these do not have a large or clear functional role in modern organisms. Examples of vestigial structures include the hind leg bones in whales, the wings on flightless birds, and pelvic bones in some snakes that no longer have legs. Vestigial structures can be seen as remnants of past common ancestors that had functional versions of these structures.
Therefore, the structures that share a common ancestry are not only vestigial but also include homologous structures, which are similar because of their origin from a common ancestor and may retain the same general layout yet have evolved differently according to each species' needs and environment.