1. Department of Palaeobiology, Royal Ontario Museum, 100 Queen's Park, Toronto, Ontario, M5S 2C6, CanadaDepartment of Zoology, University of Toronto, Toronto, Ontario, M5S 3G5, Canada
2. Bernard Price Institute for Pelaeontological Research, University of Witwatersrand, Johannesburg, PO Wits, 2050, South Africa