1. Department of Paleobiology, National Museum of Natural History, Smithsonian Institution, Washington, DC 20013-7012, USA
2. Department of Geology, University of Cincinnati, Cincinnati, OH 45221, USA
3. Department of Biology, University of New Mexico, Albuquerque, NM 87131-0001, USA
4. Environmental Sciences Division, Oak Ridge National Laboratory, Knoxville, TN 37831, USA
5. Department of Integrative Biology, U.C. Museum of Paleontology, University of California, Berkeley, CA 94720-3140, USA
6. Department of Biology, Stanford University, Stanford, CA 94035, USA