[1] Univ Sheffield, Sch Biosci, Alfred Denny Bldg,Western Bank, Sheffield S10 2TN, England
[2] Univ Witwatersrand, Evolutionary Studies Inst, ZA-2050 Johannesburg, South Africa
[3] Iziko South African Museum, Karoo Palaeontol, ZA-8000 Cape Town, South Africa
[4] Univ Cape Town, Dept Geol Sci, ZA-7701 Rondebosch, South Africa