1. 1 Department of Paleobiology, Smithsonian Institution, Washington, D. C. 20012-7012 USA
2. 2 Mathematics and Statistics, Smithsonian Institution, Washington, D. C. 20012-7012 USA
3. 3 Department of Geological Sciences, East Carolina University, Greenville, North Carolina 27858 USA
4. 4 Ocean and Earth Science, National Oceanography Centre, Southampton, SO14 3ZH UK
5. 5 National Oceanography Centre, European Way, Southampton, SO14 3ZH UK