Question

mollusk fossils were excavated and collected from a coastal cliff. scientists studying the fossils observed patterns of changing shell shape in the mollusks. the scientists identified a period of stability or stasis, followed by rapid change, and then stasis again with regard to shell shape. which of the following statements best predicts the result of a comparison between the fossils found before and after the period of rapid change?
a the same species will be found in both static periods, but they will have different shell shapes.
b the same species will be found in both static periods, but the species in the second static period will have smaller shells due to the stress of undergoing rapid change.
c most of the species found in the first static period will be absent in the second static period.
d most of the species found in the second static period will resemble each other more than the species found in the first static period.

Explanation:

The scenario describes punctuated equilibrium (stasis → rapid change → stasis) in mollusk shell shape. In punctuated equilibrium, a species remains relatively stable (stasis) and then undergoes rapid evolutionary change (like shell shape) but remains the same species (no mass extinction of the original species, ruling out C). Option A aligns: same species in both stasis periods, different shell shapes due to the rapid change. Option B’s “smaller shells due to stress” is not supported (rapid change is evolutionary, not stress - induced size reduction). Option D’s “resemble each other more” is not a key prediction of punctuated equilibrium for this context.

Answer:

A. The same species will be found in both static periods, but they will have different shell shapes.