1. Evolutionary Studies Institute and School of Geosciences, University of the Witwatersrand, Private Bag 3, WITS 2050, South Africa
2. Department of Ecosystem and Landscape Dynamics, Institute for Biodiversity and Ecosystem Dynamics (IBED), University of Amsterdam, Science Park 904, 1098 XH Amsterdam, The Netherlands
3. Council for Geoscience, Private Bag X112, Pretoria, 0001, South Africa
4. University of Johannesburg, Department of Geology, P.O. Box 524, Auckland Park, 2006, Johannesburg, South Africa