Dramatic changes in sea level occurred throughout the Cenozoic era and the rise and fall of sea level is recorded in the rocks of
the
Amazing numbers of fossil clams, snails, and sand dollars can be found in these marine rocks, along with
fossilized whale bones and shark teeth
A)
Plateau
Piedmont
Coastal Plain
D)
Valley and Ridge

the right option is; decreased genetic variation  

decreased genetic variation describes the effect of this environmental change.

genetic variation is the naturally occurring genetic diversities or differences between organisms of the same species in a population. genetic variation allows the survival and adaptability of a species when they encounter changing environmental conditions. when an endangered species reduces, it loses genetic variation which may not be restored even if the species rebound and will only be recovered through the gradual collection of mutations over many years.