Miocene paleosols and habitats of Proconsul on Rusinga Island, Kenya

Abstract

Abstract Early Miocene (18 Ma) volcaniclastic deposits of the Hiwegi Formation on Rusinga Island include at least six distinct kinds of paleosols, representing different parts of former ecosystems. Four localities (R1 site of L. S. B. Leakey, nearby site of Pickford, R106 of M. Leakey, and Kaswanga site of Walker) for articulated or cranial material of two species of Proconsul are all in the same kind of paleosol. These are here called Chuodho paleosols, and represent woodlands early in ecological succession of streamsides. Proconsul heseloni is best known from the lower Hiwegi and Kiahera Formations, and was replaced in the same habitat by P. nyanzae in the geologically younger middle Hiwegi Formation. In contrast, articulated skeletons of Dendropithecus macinnesi were found in another kind of paleosol (here called Tek), representing dry upland forest including hackberries ( Celtis rusingensis ). Other paleosols represent other kinds of early successional vegetation, woodland and dambo grassy woodland. Paleoclimate was dry (300-650 mm mean annual precipitation) and mildly seasonal. The paleosols formed along braided streams on outwash and airfall ash of a carbonatite-nephelinite volcano. The Hiwegi Formation accumulated during the building of this volcano about 18 million years ago.