1. Department of Organismal Biology and Anatomy, University of Chicago, Chicago, IL 60637-1508, USA
2. UCD School of Biology and Environmental Science, UCD Science Education and Research Centre (West), UCD Earth Institute, University College Dublin, Belfield, Dublin 4, Ireland
3. School of Geography, Earth and Environmental Sciences, University of Birmingham, Birmingham B15 2TT, UK
4. Department of Zoology, Cambridge University, Cambridge CB2 3EJ, UK
5. Center for Advanced Radiation Sources, University of Chicago, Chicago, IL 60637-1508, USA
6. Department of Radiology, University of Chicago, Chicago, IL 60637-1508, USA