Final answer:
A fossil found in one layer resembling a fossil in another suggests they may have an evolutionary link or come from a similar time period. Such similarities can indicate either contemporaneity or a common ancestor, like in the case of the Archaeopteryx fossil. DNA sequence comparisons further support relatedness among species.
Step-by-step explanation:
If a fossil found in layer B resembles a fossil found in layer A, this similarity suggests that the organisms from both layers may be related or from the same time period, indicating a possible evolutionary link or consistency in the deposition of sedimentary layers.
When analyzing fossils to determine relatedness, paleontologists will often consider the morphology, or structure, of the fossils. Fossils that are similar in shape or structure can indicate that the organisms were either contemporary (lived during the same period), or share a common ancestor. For instance, the discovery of an Archaeopteryx fossil, which has features of both reptiles and birds, supports the concept that modern species share a common ancestor, highlighting the evolutionary connections between different groups.
DNA sequences are also used as evidence in determining relatedness among organisms, with more closely related species showing more similarities in their DNA. When comparing fossils from a layer associated with a mass extinction event, one may find evidence of a sudden decrease in the diversity and number of species, as well as changes in the types of organisms found before and after the event, which supports the theory of common ancestry.