Paleoanthropology of the Malawi Rift: An early hominid mandible from the Chiwondo Beds, northern Malawi

Abstract

Abstract The Hominid Corridor Research Project has recovered a mandibular corpus, UR 501, containing third and fourth premolars and first and second molars in variable states of preservation, from Late Pliocene paleolake Malawi sediments at Uraha in northern Malawi. A qualitative description is accompanied by quantitative measures of the corpus, tooth crowds and roots, and enamel microanatomical features. Many absolute and relative measures respecting molar and premolar crown shape indices, some relative cusp areas, and enamel microanatomical features, as well as fissure patterns and crown morphology, are within the sample range of early Homo , though some are within the limits of variation represented by Australopithecus ( A. africanus and A. afarensis ). However, UR 501 has absolutely large molar crown areas, P 3 relative expansion of the talonid, plate-like P 3 and P 4 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 Pliocene fossils from east of Lake Turkana, Kenya, that have relatively large brains and robust jaws and teeth and that have been referred to Homo rudolfensis Alexeev, 1986, by Wood (1992 b ), and to which we also refer UR 501. Faunas that are both associated with UR 501 and provide some biochronological control indicate a date between 2·5 and 2·3 Ma. The palaeobiogeographic significance of UR 501 lay in its association with an assemblage dominated by eastern African endemic taxa. We provide the palaeobiogeographic implications of the Chiwondo Beds faunal assemblages (cf. Bromage et al. , 1995) to suggest that Homo rudolfensis arose in eastern Africa during, and partly as a result of, the ca. 2·5 Ma climatic cooling event. It remained endemic there while southern African taxa were dispersing toward the equator. The pattern to emerge from our paleobiogeographic perspectives on other hominid taxa is that early hominids arose successively in the eastern African tropical ecological 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.