1. Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge CB2 3EQ, UK
2. School of Earth Sciences, The University of Western Australia, 35 Stirling Highway, Crawley, WA 6009, Australia
3. Larson Paleontology Unlimited, 12799 Wolframite Road, Keystone, South Dakota 57751, USA
4. Department of Mining Engineering and Management, South Dakota School of Mines and Technology, Rapid City, South Dakota 57701, USA