1. Geology Department, Pomona College, 185 E. Sixth St., Claremont, California 91711, USA
2. Department of Earth and Planetary Sciences, University of California, Davis, One Shields Drive, Davis, California 95616, USA
3. Department of Land, Air and Water Resources, University of California, Davis, One Shields Drive, Davis, California 95616, USA
4. Department of Natural History, Palaeobiology, Royal Ontario Museum, 100 Queen's Park, Toronto, Ontario M5S 2C6, Canada
5. Department of Ecology and Evolutionary Biology, University of Toronto, 25 Willcocks Street, Toronto, Ontario M5S 3B2, Canada