1. Society of Fellows, Harvard University, Cambridge, MA 02138, USA
2. Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, MA 02138, USA
3. Scripps Institution of Oceanography, University of California, San Diego, La Jolla, CA 92037, USA
4. Museum of Paleontology, Department of Earth and Environmental Sciences, University of Michigan, Ann Arbor, MI 48109, USA
5. Department of Earth Sciences, University of Oxford, Oxford OX1 3AN, UK
6. Department of Geology and Geophysics, Yale University, New Haven, CT 06511, USA
7. Department of Paleobiology, National Museum of Natural History, Smithsonian Institution, Washington, DC 20013, USA