Paleobiogeography of the Malawi Rift: Age and vertebrate paleontology of the Chiwondo Beds, northern Malawi

The Hominid Corridor Research Project has conducted paleontological surveys of Plio-Pleistocene deposits (Chiwondo Beds) in northern Malawi with the aim of characterizing the geographic role of southeast Africa in the origin and dispersion of Plio-Pleistocene faunas including early hominids. The faunal assemblages derive from two main fossil bearing regions (northerly localities near the town of Karonga, and more southerly localities near the village of Uraha) within the Malawi Rift. These assemblages date from somewhat older than 4.0 Ma to less than 1.6 Ma based on biochronological comparisons to radiometrically dated biostratigraphic horizons in eastern Africa. Comparisons between the Chiwondo Beds fauna and endemic Plio-Pleistocene faunas of eastern and southern Africa indicate that the Malawi Rift belongs largely within the paleoecological domain of eastern Africa, though it also records the northernmost transgressions of several southern African endemic taxa. Continental position and climatic conditions responsible for the tropical/temperate zonation in Africa are suggested to partly account for the large mammal barrier in the vicinity, of the Zambezian Ecozone today. However, faunal dispersion from southern to eastern Africa dominates after 2.5 Ma suggesting that this zonation drifted equator-ward during Late Pliocene climate change in accordance with the "Habitat Theory" of Vrba (1992). Interpretation of the Chiwondo Beds faunal assemblage has potential implications for the presumed dates of first appearance in southern African Pliocene assemblages, and may further contribute ecological criteria to scenarios of faunal phylogenesis.