Rusinga Island Fossil Sites

Rusinga holds one of the richest early Miocene fossil deposits in Africa, and the ape skull found here in 1948 is a landmark of twentieth century palaeontology. The sites themselves are eroding hillsides on a farmed, inhabited island, with no visitor centre, no boardwalk and no ticket office, and what a visitor gets out of them depends almost entirely on who walks the ground with them.

Why the Rusinga Beds Matter

Most fossil localities preserve bones. Rusinga preserves a landscape. A sequence of explosive eruptions from a nearby volcanic centre buried an early Miocene forest in ash, taking plants, insects and animals together, which is vanishingly rare. More than a hundred vertebrate species are known from the beds alongside fossil leaves, fruits, seeds and invertebrates, which is what allows the environment to be reconstructed rather than guessed at.

The island exposes a stacked sequence of formations, of which the Hiwegi is the best known, with the Kiahera and Kulu formations also named in the literature. On age, older popular accounts settle on a single figure of about 18 million years. More recent radiometric work has widened that, with published age constraints for the Rusinga and neighbouring Mfangano faunas placing the main beds at roughly 20 to 17 million years. Either figure is defensible attached to the work it comes from; neither should be quoted as a settled single number.

The 1948 Skull, and the Name That Has Changed

On 2 October 1948, during the Leakey expedition’s work on the island, Mary Leakey found a fossil ape skull, the first reasonably complete one known. It was published in Nature that year under the title Skull of Proconsul from Rusinga Island and became a reference specimen in the study of early apes. Two later revisions changed what it is called, and travel copy has caught up with neither.

• 1993. Alan Walker and colleagues separated a distinct species and named it heseloni, after Heselon Mukiri, the Kenyan field assistant who completed the excavation of the 1948 skull. Until then the Rusinga material had mostly been lumped under Proconsul africanus.
• 2015. Kieran McNulty and colleagues published a systematic revision of Proconsul in the Journal of Human Evolution and erected a new genus, Ekembo, moving the Rusinga and Mfangano species into it. The Rusinga ape is therefore Ekembo heseloni in current usage, with the larger Ekembo nyanzae alongside it.

None of that diminishes the find. Palaeontological names are hypotheses about relationships and get revised when the material improves, so a guide or a sign at Rusinga saying Proconsul is not wrong so much as out of date.

Kaswanga and the Skeletons

The other event that made the island’s reputation happened in the 1980s. Excavation at the Kaswanga Primate Site, begun in 1984 by Alan Walker, Mark Teaford and colleagues as a joint National Museums of Kenya and Johns Hopkins University expedition, recovered over a thousand bones belonging to around ten individuals of the same species, including nine partial skeletons collected across 1984 and 1985.

That matters because early ape fossils are usually teeth and jaw fragments. Associated skeletons let researchers ask how the animal moved, and the Kaswanga material has underpinned decades of work on the limbs and body plan of early apes.

A Second, Much Younger Record

Rusinga has an archaeological record as well as a palaeontological one, and the two are separated by nearly twenty million years. The Wasiriya Beds carry Pleistocene deposits with Middle Stone Age artefacts and associated fauna, a completely different body of research. Rusinga is therefore not one site but two overlapping bodies of evidence in the same landscape, and a guide explaining one may not be describing the other. Archaeological tours in Kenya covers how the country’s prehistoric record fits together.

What Is Actually Visible

Exposed sediments, gullies and eroding slopes, with fossil material weathering out of them. There are no interpretation boards, no fenced excavation to look into and, at most localities, nothing to mark the ground as different from the ground either side.

Walking with someone who can read the exposures changes the visit completely. A guide who works the fossil sites can point out which band of sediment is which, show bone fragments lying where they have weathered out, and place the 1948 find and the Kaswanga excavations in the actual ground. Without that, it is a hot walk on a bare hillside.

Collecting fossils is illegal in Kenya, and at a surface locality it also destroys the information. A fragment picked up and pocketed loses its stratigraphic position, which is most of what made it useful. Photograph what is on the ground, show the guide, and leave it where it lies.

Arranging a Visit

The localities sit on private and community land, with no gate and no published admission charge. Access is arranged locally, through accommodation on the island or a guide introduced in Mbita, and a fee for the guide and for landowner permission is normal and should be agreed before setting out.

Rusinga is the only Kenyan island on Lake Victoria that can be driven onto, so reaching it is straightforward even though reaching the localities is not. Practical points:

• The ground is open, dry and hot, with no shade at the exposures. Early morning is the workable window.
• Sturdy shoes matter on loose eroding slopes, and the going is steeper than the island looks from the road.
• Carry water in, and allow half a day for one or two localities.

The island’s other draws are covered on the Rusinga Island page, and the rock art on neighbouring Mfangano is the natural pairing for anyone here for the deep past.

Questions Travellers Ask About the Rusinga Fossil Sites