Abstract
Abstract. In terminal Pliocene–early Pleistocene times, part of the Malawi Basin was occupied by paleo-lake Chiwondo. Molluscan biostratigraphy situates this freshwater lake either in the East African wet phase between 2.7–2.4 Ma or that of 2.0–1.8 Ma. In-lake divergent evolution remained restricted to a few molluscan taxa and was very modest. The lacustrine Chiwondo fauna went extinct at the beginning of the Pleistocene. The modern Lake Malawi malacofauna is depauperate and descends from ubiquistic southeast African taxa and some Malawi basin endemics that invaded the present lake after the Late Pleistocene mega-droughts. The Pleistocene aridity crises caused dramatic changes, affecting the malacofauna of all East African lakes. All lacustrine endemic faunas that had evolved in the Pliocene rift lakes, such as paleo-lake Chiwondo, became extinct. In Lake Tanganyika, the freshwater ecosystem did not crash as in other lakes, but the environmental changes were sufficiently important to trigger a vast radiation. All African endemic lacustrine molluscan clades that are the result of in-lake divergence are hence geologically young, including the vast Lavigeria clade in Lake Tanganyika (ca. 43 species).
Highlights
Introduction of the DesmondClark collection was studied by GautierThe hypothesis that the large African lakes are “natural lab-bapynhdAte.axGroeonrothmnyeran(udnbpiuobs--oratories of evolution” and that their diversified molluscan lished data, 1995)
This study is based on the collections of terminal Pliocene– early Pleistocene molluscs collected in the Chiwondo region (NW margin of Lake Malawi), respectively, in the 1960s during the Desmond ClarkOPcaleaeaon-AnStrcopieolnogciceal Investigation and in 1980–1990s during the Hominid Corridor Research Project led by Timothy Bromage and Friedemann Schrenk
The data advanced in this paper indicate that regardless of these depth and size, all African freshwater systems, that in the Lake Malawi Basin included, crashed during the Pleistocene and that their endemic intra-lacustrine faunas went extinct
Summary
This study is based on the collections of terminal Pliocene– early Pleistocene molluscs collected in the Chiwondo region (NW margin of Lake Malawi), respectively, in the 1960s during the Desmond ClarkOPcaleaeaon-AnStrcopieolnogciceal Investigation and in 1980–1990s during the Hominid Corridor Research Project led by Timothy Bromage and Friedemann Schrenk. Albrecht Gorthner, the HCRP malacologist, sampled the Holocene assemblages near the Shire River outlet and this preliminary investigation was recently continued Bocxlaer, 2004; Van BocxlaeSr eot laild., 2E01a2r).thAll relevant fossil material collected in the Malawi Basin is provisionally stored at the Paleontological Research Unit, Ghent University, awaiting formal taxonomic description.
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