Rescue Excavation of Large Mammal Skeleton and Associated Stone Tools from Temporarily Exposed Section, Lake Victoria, Kenya

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Whilst investigating potential Middle Stone Age sites in Kenya in September 2009 Prof T. Brown accompanied Dr L. Basell and discovered a deep gully in sediments on the shore of Lake Victoria near a town called Chianda on the Uyoma Peninsula which was actively eroding revealing bones and artefacts. They were looking for lithics and former shorelines of Lake Victoria, when they noticed semi-articulated large mammal bones and a tusk protruding from the actively eroding slope. Closer examination revealed further fossilised bone fragments from smaller mammals some of which appeared to be cut marked, and skull fragments. Strewn over and around the eroding face were stone tools including both flakes and cores of lavas, tuffs and quartz. Basell (a stone tool specialist) considers these to be of Middle Stone Age antiquity. The Middle Stone Age is a period in Africa that is thought to last from about 500,000-50,000 years ago and is associated with the evolution of the earliest members of our species, Homo sapiens but there are very few sites which have been well dated. Finding fossils and lithics of this age together is extremely unusual and important in an eastern African setting, as soil conditions are generally acidic and bone of does not preserve well. However, the researchers also knew that during the 1930s Archdeacon Owen, a keen archaeologist and close colleague of Louis Leakey conducted survey and made collections near Chianda. He collected fossil and lithic material but did not excavate. He believed the fossilised fauna he found was Miocene in age and part of a sequence of deposits called the Hiwegi Formation. Owen had collected material from other Miocene sites to the east and south of Chianda in places such as Rusinga Island where the Hiwegi Formation is now thought to be >18 million years old. Western Kenya is well known for its Miocene fossils, and a wide array of animal and plant remains has been found at several sites where research has been concentrated over decades. In certain places on Rusinga, these sites contain incredibly well preserved twigs, nuts and berries, and new faunal species continue to be discovered despite 80 years of research there. These sites are perhaps best known because they have yielded remains of a very early primate called Pro Consul which some researchers think is a distant ancestor of Homo sapiens. The precise age of the faunal and floral fossils is still debated, and there is some confusion about how the different sites researched over the years relate to each other, and exactly what the environmental conditions were like beyond specific sites. For example, was there a lake here during the Miocene? The present Lake Victoria is about the size of Ireland but previous research has suggested that the lake only formed about 400,000 years ago and may have dried up entirely several times since then as a result of large-scale climatic fluctuations. Very little is known about the regional environment prior to this. Whether the Chianda site is Miocene or more recent, the vertebrate remains in this condition are old and rare. The deposits from which they are eroding are limited in extent and the position of the vertebrae and tusk suggests that some of the carcass or carcasses may have already been eroded away. This project is a rescue excavation to preserve this unusual find and any other fossils or artefacts found with it before it is destroyed. Further examination of the stratigraphic sequence at Chianda by Prof. Brown, a palaeoenvironmental specialist, indicated that there were deposits here which could be dated and that the deposits indicate a marsh edge or a shallow river/lake environment. With three further experts Dr J. Stewart, Dr. I. Boomer and Dr I. Onjala, they will try and find out what the animal is, how old the site is and take samples so we can learn about previous environmental conditions in the area and how they relate to past climatic change.