PALEOANTHROPOLOGY OF THE MALAWI RIFT - AN EARLY HOMINID MANDIBLE FROMTHE CHIWONDO BEDS, NORTHERN MALAWI

The Hominid Corridor Research Project has recovered a mandibular corpu s, UR 501, containing third and fourth premolars and first and second molars in variables states of preservation, from Late Pliocene paleola ke Malawi sediments at Uraha in northern Malawi. A qualitative descrip tion is accompanied by quantitative measures of the corpus, tooth crow ns and roots, and enamel microanatomical features. Many absolute and r elative measures respecting molar and premolar crown shape indices, so me relative cusp areas, and enamel microanatomical features, as well a s fissure patterns and crown morphology, are within the sample range o f early Homo, through some are within the limits of variation represen ted by Australopithecus (A. africanus and A. afarensis). However, UR 5 01 has absolutely large molar crown areas, P3 relative expansion of th e talonid, plate-like P3 and P4 roots, and some enamel microanatomical features that correspond more closely to the Paranthropus condition. Taken altogether, UR 501 corresponds closely to the subset of Late Pli ocene fossils from east of Lake Turkana, Kenya, that have relatively l arge brains and robust jaws and teeth and that have been referred to H omo rudolfensis Alexeev, 1986, by Wood (1992b), and to which we also r efer UR 501. Faunas that are both associated with UR 501 and provide s ome biochronological control indicate a date between 2.5 and 2.3 Ma. T he palaeobiogeographic significance of UR 501 lay in its association w ith an assemblage dominated by eastern African endemic taxa. We provid e the palaeobiogeographic implications of the Chiwondo Beds faunal ass emblages (cf. Bromage et al., 1995) to suggest that Homo rudolfensis a rose in eastern Africa during and partly as a result of, the ca. 2.5 M a climatic cooling event. It remained endemic there while southern Afr ican taxa were dispersing toward the equator. The pattern to emerge fr om our paleobiogeographic perspectives on other hominid taxa is that e arly hominids arose successively in the eastern African tropical ecolo gical domain. During favorable periods, some early hominids dispersed southward beyond the Zambesian Ecozone, evolved there, perhaps due to relative isolation and/or due to factors associated with its temperate ecology, and became endemic there.