1. a Department of Geology , The Field Museum , 1400 South Lakeshore Drive, Chicago , Illinois , 60605 , USA E-mail:
2. b Burke Museum and Department of Biology , University of Washington , Seattle , Washington , 98195 , USA E-mail:
3. c Division of Paleontology , American Museum of Natural History and Lamont-Doherty Earth Observatory, Columbia University , 61 Rt. 9W, Palisades , New York , 10964 , USA E-mail:
4. f Jackson School of Geosciences, The University of Texas at Austin , TX , 78712 , USA
5. d Karoo Palaeontology, Natural History Division , Iziko, South African Museum , PO Box 61, Cape Town , 8000 , South Africa E-mail:
6. e Humboldt Universität zu Berlin, Museum für Naturkunde , D10099 , Berlin , Germany E-mail: