PALEOBIOGEOGRAPHY OF THE MALAWI RIFT - AGE AND VERTEBRATE PALEONTOLOGY OF THE CHIWONDO BEDS, NORTHERN MALAWI

The Hominid Corridor Research Project has conducted paleontological su rveys 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 ear ly hominids. The faunal assemblages derive from two main fossil bearin g regions (northerly localities near the town of Karonga, and more sou therly localities near the village of Uraha) within the Malawi Rift. T hese assemblages date from somewhat older than 4.0 Ma to less than 1.6 Ma based on biochronological comparisons to radiometrically dated bio stratigraphic horizons in eastern Africa. Comparisons between the Chiw ondo Beds fauna and endemic Plio-Pleistocene faunas of eastern and sou thern Africa indicate that the Malawi Rift belongs largely within the paleoecological domain of eastern Africa, though it also records the n orthernmost transgressions of several southern African endemic taxa. C ontinental position and climatic conditions responsible for the tropic al/temperate zonation in Africa are suggested to partly account for th e 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 assemblag e has potential implications for the presumed dates of first appearanc e in southern African Pliocene assemblages, and may further contribute ecological criteria to scenarios of faunal phylogenesis.