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.