Palaeoecological significance of palms at Olduvai Gorge, Tanzania, based on phytolith remains

Abstract

Palms are among the most abundant, diverse and economically important families of plants in tropical and subtropical regions of the world; their number and diversity make them an important part of the ecosystem. Phytoliths are abundantly produced in palms, mainly the spheroid echinate type and, although their number decreases notably after their deposition in soils, they remain stable for long periods of time. Palm phytoliths were recovered from sediments at HWKEE, on the eastern palaeolake margin of the Olduvai basin during Lowermost Bed II (between Tuffs IF and IIA, 1.795–1.71 Ma). Their abundance in trench 107 (the only freshwater source recognised to date) occurs in three stratigraphically consecutive layers, the first one located immediately above the incision layer (40 cm above Tuff IF). Above these samples there are no palm phytoliths in the fossil record. The identification of the type of palms represented will be useful for determining the landscape distribution and nature of hominin activities along the lake margin and alluvial fan of the central Olduvai Basin. Here we use morphometric analysis of spheroid echinate phytoliths from fossil and modern palms ( Phoenix reclinata and Hyphaene petersiana) and their corresponding soils to determine if the differences are significant and can be confidently applied to the fossil samples. Fossil and modern soil samples were found to be very similar to each other but the spheroid echinates from the fossil soils were bigger than the modern soil samples. Either the palms from the samples were different or there is a strong bias towards preserving phytoliths from the smaller end of the range. If this is the case then the implication would be that the fossil samples are the leaves and inflorescences of Phoenix reclinata. A wider variety of modern palms needs to be analysed.