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The Smithsonian’s initial excavations at the nearby site of Kanjera in 1987 and 1988 gave our research team an opportunity to explore the eroded gullies of Kanam, located about 3 to 7 km to the west of Kanjera. The Kanam surveys turned up very few stone tools but hundreds of fossilized bones of diverse mammals. Initial geological dating by the Berkeley Geochronology Center (Berkeley, California) yielded dates for the lowest (and oldest) unit – the Kanam Formation – of approximately 6.1 to 5.1 million years old. Fossil species from the overlying Homa Formation resemble those found in the 3.6-million-year-old beds of Laetoli, Tanzania, dated around 3.6 million years old. Excavations led by Rick Potts in 1995-96 at Kanam West (the westernmost of three gully systems in the Kanam vicinity) yielded fossils of late Miocene and mid-Pliocene age. Further work awaited detailed geological studies, which began with a team assembled by Tom Plummer in the late 1990s and continuing during brief excursions to Kanam from 2002-2007. Excavations led by Plummer (CUNY Queens College, Smithsonian, National Museums of Kenya combined expedition) in the Kanam East and Kanam Central gullies have yielded fossils younger than 3 million years old. New work by the Smithsonian team is getting started, focused on new research on the 6 million-year-old sediments of Kanam West and Kanam Central.
Following initial fossil collecting at Kanam in the early 1900s, Louis Leakey commenced excavations and surveys for fossils during the early 1930s. One fossil in particular – the Kanam mandible, discovered by Leakey’s team in 1932 – proved very controversial, and embroiled Leakey in a difficult defense of his professional reputation, largely in response to observations published by the geologist P.G.H. Boswell in the journal Nature in 1935. Boswell claimed that the recording of the mandible and other key fossils at Kanam and Kanjera were inprecise, and thus the age and associations of other fossil animals with the Kanam mandible could not be verified. The reason why this was important is that the jaw showed similarities to that of the genus Homo, possibly even H. sapiens, despite the jaw’s irregular shape, and Leakey claimed that the human genus and possibly even our species had a very long history dating to a time of animal species that had long been extinct. Boswell’s first claim, then, undercut one of the vital pieces of Leakey’s 1930s view of human evolution. Boswell also claimed that the Kanjera sediments were slumped due to gravity flow while wet, and thus provided no reliable stratigraphy in which the fossils could be placed as either older or younger. The Smithsonian excavations at Kanjera in 1987 recorded approximately 44 meters of stacked sedimentary layers, without slumping, indicating that this second claim of Boswell’s was incorrect.
As for the Kanam mandible, studies by our team led by J. Phelan, M.J. Weiner, J.L. Ricci, and T. Plummer, confirmed an earlier study by Phillip Tobias (University of the Witwatersrand), and indicate that a swelling on the bottom of the mandible near the midline was the result of a pathological growth following fracture of the jaw, while other fracturing of the bone took place after the individual died. Our team concluded as follows: The Kanam mandible, after tens of thousands of years in lime-rich sediments, retained its calcium phosphate bone composition. Furthermore, while geological processes have fractured the specimen, both its macro- and microanatomy are consistent with bone pathology secondary to fracture.
Source of information on the Kanam mandible pathology: Pathology of an archaic Homo mandible from Kanam, Kenya, Presented at the International Association for Dental Research. Weiner, M.J. (1), Ricci, J.L. (2), Phelan, J., (2), Plummer, T. (3), Gauld, S. (4), Potts, R. (5), Bromage, T.G. (2)
(1) New York University College of Dentistry, USA, (2) New York University, USA, (3) Queens College, City University of New York, USA, (4) Santa Monica College, USA, (5) Smithsonian Institution, USA