E-Mail IMAGE: A seminal 1981 study organized the a history of ocean life into three hierarchies, with certain animals reigning the seas during each time periods. Two mass extinctions cleared the way... view more Credit: Jeff Gage/Florida Museum of Natural History GAINESVILLE, Fla. --- Evolutionary arms races between marine animals overhauled ocean ecosystems on scales similar to the mass extinctions triggered by global disasters, a new study shows. Scientists at Umeå University in Sweden and the Florida Museum of Natural History used paleontological databases to build a multilayered computer model of the history of marine life over the last 500 million years. Their analysis of the fossil record closely echoed a seminal 1981 study by paleontologist J. John Sepkoski - with one key difference.