1. Centre for Ecological and Evolutionary Synthesis, Department of Biology, University of Oslo, N-0316 Oslo, Norway
2. Department of Organismic and Evolutionary Biology
3. Department of Invertebrate Paleontology, Museum of Comparative Zoology, Harvard University, Cambridge, MA 02138, USA
4. Present address: Department of Integrative Biology, University of California Museum of Paleontology, University of California, Berkeley, CA 94720, USA