1. University Museum of Zoology Cambridge; Downing Street Cambridge CB2 3EJ UK
2. Department of Geology; University of Leicester; Leicester LE1 7RH UK
3. British Geological Survey; The Lyell Centre; Research Avenue South Edinburgh EH14 4AP UK
4. Committee on Evolutionary Biology; University of Chicago; Culver Hall, 1025 East 57 Street Chicago IL 60637 USA