Short-spined sea urchin fossils were found directly above long spined sea urchin fossils in a layer of rock. What do the differences between the two sets of sea urchin fossils suggest about them?


A. The longer spines developed as the shorter-spined sea urchins grew older.


B. The longer-spined sea urchins existed before the shorter-spined sea urchins.


C. The shorter-spined sea urchins stretched their spines to ward off predators.


D. The shorter spines did not protect the sea urchins well enough and they died off.