MIOCENE PALEOSOLS AND HABITATS OF PROCONSUL ON RUSINGA ISLAND, KENYA

Early Miocene (18 Ma) volcaniclastic deposits of the Hiwegi Formation on Rusinga Island include at least six distinct kinds of paleosols, re presenting different parts of former ecosystems. Four localities (R1 s ite of L. S. B. Leakey, nearby site of Pickford, R106 of M. Leakey, an d Kaswanga site of Walker) for articulated or cranial material of two species of Proconsul are all in the same kind of paleosol. These are h ere called Chuodho paleosols, and represent woodlands early in ecologi cal succession of streamsides. Proconsul heseloni is best known from t he lower Hiwegi and Kiahera Formations, and was replaced in the same h abitat by P, nyanzae in the geologically younger middle Hiwegi Formati on. In contrast, articulated skeletons of Dendropithecus macinnesi wer e found in another kind of paleosol (here called Tek), representing dr y upland forest including hackberries (Celtis rusingensis). Other pale osols represent other kinds of early successional vegetation, woodland and dambo grassy woodland. Paleoclimate was dry (300-650 mm mean annu al precipitation) and mildly seasonal. The paleosols formed along brai ded streams on outwash and airfall ash of a carbonatite-nephelinite vo lcano. The Hiwegi Formation accumulated during the building of this vo lcano about 18 million years ago. (C) 1995 Academic Press Limited