Question

this diagram of the fossil record represents changes in mollusks over millions of years.
mollusks in the fossil record
how can the pattern of change in the fossil record best be explained?
a the mollusks were well adapted to their stable environment. a large, sudden change occurred in their environment. after the change the mollusks with the bigger shells were better adapted for the new environment.
b the mollusks were well adapted to their stable environment. the mollusks hybridized with a smaller species of mollusk. a new species of mollusk with a bigger shell resulted.
c the mollusks were not well adapted to their environment. the length of the mollusks shells changed gradually over time. the mollusks in the original population that had small shells died over a period of many years.

Explanation:

• Option A: The fossil record shows stasis (little change) initially (mollusks well - adapted to stable environment). Then there is a rapid change (a large, sudden environmental change). After the change, the new form (bigger - shelled mollusks) is in stasis again (better adapted to the new environment). This matches the pattern of punctuated equilibrium (long periods of stability interrupted by rapid change).
• Option B: There is no indication in the fossil - record diagram of hybridization. The change seems more related to environmental change and adaptation rather than hybridization.
• Option C: The initial part of the fossil record shows stasis, which implies the mollusks were well - adapted. Also, the change is rapid, not gradual as described in this option.

Answer:

A. The mollusks were well adapted to their stable environment. A large, sudden change occurred in their environment. After the change the mollusks with the bigger shells were better adapted for the new environment.