The Plio-Pleistocene vegetation and climate of Sterkfontein and Swartkrans, South Africa, based on micromammals

Micromammalian remains from Oldowan and Acheulean horizons in Sterkfontein Member 5E (M5E-O and M5E-A) and Swartkrans Members 1–3 (SKX1–3) provide information for the period between about 2 and 1Ma. Another small sample from Sterkfontein Member 4 (M4) refers to a short period around 2·8–2·6Ma and material from Sterkfontein post Member 6 infill (post-M6) relates to the Middle Stone Age occupation around 100ka. Virtual absence of evidence of digestion on in situ lower molars of the major prey species, Mystromys albicaudatus, indicates that one of the owls Tyto alba, T. capensis or Asio capensis was the responsible predator. Over-emphasis on riverine grassland supports this suggestion, as does faunal resemblance between the Sterkfontein Valley samples and modern prey samples for the three owl species concerned. The location of the roost and the range of prey species point to the barn owl T. alba. There is no indication of differential bias between samples. South African species of eagle owl (Bubo spp.) are ruled out. All samples appear to represent interglacial conditions. The Grassland—Savanna ecotone probably lay nearby, as did the border between Moist and Arid Savanna. Possible modern analogues occur about 200km west and southwest of the valley more than 250m lower in altitude. South of Mafikeng all three vegetation types intergrade but the rainfall is higher than that postulated for some of the units in the Sterkfontein Valley. Similar climatic conditions occur near Kuruman and Kimberley where Arid Savanna merges into Grassland. Landscape information indicates a succession from riverine grassland, sometimes withAcacia trees, through hillsides with bush, grass and some trees, to plains with open savanna woodland. The suggested climate for the Sterkfontein Valley varied between ±310mm and possibly 550mm mean annual precipitation, summer aridity index 3·8–4·1 and percentage winter rainfall 23–24. Minimum and maximum monthly temperatures would have been higher than they are today but with the temperature range reduced.