1. Museum of Comparative Zoology, Harvard University, Cambridge, MA 02138, USA
2. Department of Biological Sciences, University of Alberta, Edmonton, Alberta, Canada T6G 2E9
3. Department of Ecology and Evolutionary Biology, University of Toronto, Toronto, Ontario, Canada M5S 3B2
4. Department of Geological Sciences, University of Manitoba, 125 Dysart Road, Winnipeg, Manitoba, Canada R3T 2N2