According to paragraph 2, what do the minerals in the delta rocks containing rhipidistian crossopterygian fossils reveal? A. These deltas formed in dry periods but gradually became wetter. B. These deltas contain different types of iron minerals than do the surrounding areas. C. Most rhipidistian crossopterygian fish died when the climate became dry. D. Rhipidistian crossopterygian fish lived in areas that experienced alternate dry and wet periods.