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Site history
Kanam is an archaeological site in Kenya. It lies on the eastern shores of Lake Victoria and to the south of the Winam Gulf in the Homa Peninsula, that lies between parts of the Great African Rift Valley which is a significant study area for human evolution. The site consists of three gullies, that separate Kaman-West central and east. To the east of Kanam lies the site of Kanjera. The landscape is formed by volcanic activity that began 13 million years ago (ma) and continued until 5 Ma. Homa Mountain for example is a carbonatite volcano in the Homa Peninsula. The volcanic activity has not stopped completely, even today there are active hot springs in the environment of Kanam. The volcanic depositions also make it an ideal condition for the preservation of fossils. As a matter of fact the volcanic activity was occurring while fossils were accumulating. The sediment deposition of the peninsula consists of late Miocene to Pleistocene dating deposited layers. The Homa Peninsula has recorded evidence on hominin presence over a period of 6 million years, the lacustrine sediments seem to hint towards a near constant presence of water and vegetation on the hills and slopes that surrounded the Homa Mountain. This would have made the environment quite appealing form humans in the past. The finds of Kanjera seem to suggest that the activities were sustained by multiple generations of hominins.

The site was discovered because of excavations at the nearby site of Kanjera. The first excavations were done early in the 1900s by Louis Leakey. After a hiatus they reopened the excavation in 1930 and in 1932 a controversial fossil was discovered in the area of the inland gullies at Kanam West, namely the Kanam mandible. This mandible showed similarities to the genus Homo maybe even Homo Sapiens. The geologist P.G.H. Boswell claimed in the journal Nature in 1935, that the recording of the mandible and other key fossils at Kanam and Kanjera were imprecise, and thus the age and associations of other fossil animals with the Kanam mandible could not be verified. Because of this it cannot be trusted that the possible Homo Sapiens fossil is associated with the fossils that are from much older periods than Homo Sapiens. Leakey maintained throughout his career that the mandible was found in situ with a tooth of a Deinotherium. Also, according to Leakey there was a pre-chellean tool pebble found in the same level, which he considered was enough evidence for dating the mandible in the lower Pleistocene period. Today’s attempts to find the exact locus of the Kanam mandible, using the land profiles Leakey published, have failed. This is mainly because the gully system has changed considerably since 1932. Kent (1940), who was supposedly shown the location of the Kanam Mandible by Leaky, also did a geological study of the Kanam gullies. According to him the Kanam mandible was intrusive. He pointed out that small fissures would have allowed the mandible to work its way down in a nodule into the lower Pleistocene level Based on this it seems most likely that the mandible comes either from bed R1, from one of the beds of the Apoko formation (A1-A4) or from the Kanam formation beds K3-K5. According to Pickford and Bassett the context of the mandible is within bed R1. This seems to be the most likely solution. They proposed that the Kanam mandible was first fossilized in Bed A3 of the Apoko formation where it got its distinctive surface coat of calcite. In the recent past it would have eroded from this bed and moved to bed R1 where it became associated with the older Deinotherium tooth from bed H1. The mandible must have been dislodged from bed R1, and because of this, it is considered that the Kanam mandible likely dates to the late Pleistocene to Holocene, and that it is a fragment of Homo Sapiens. Tom Plummer led a geological study at the site in the late 1990s, which were resumed with brief campaigns between 2002 and 2007. These excavations at the East Kanam gully and the Kanam central gully yielded fossils which were younger than 3 million years old. The Smithsonian team has started a new project of looking at fossilized remains of 6 million years old sediment form Kanam West and central.

Geological formations
The Oldest formation is the Kanam formation, which consists of six beds (K1-K6) of intercalated silts and airfall green/grey tuffs. These are cut by a large amount of narrow calcite dykes or sills, which are more resistant to weathering. At Kanam West the formation is nine meters thick and at other locations it was measured to 16 meters. The fauna seems to suggest that this formation is at least 4 million years old. After the deposition of bed K6 there was a period of erosion before the next period of sedimentation. During this period of erosion there were gullies formed of 3 meters deep. The Kanam formation is followed by the Homa agglomerate formation, which has a lot of erosional and angular deposits, and has two beds (H1-H2). It consists of a lag deposit with a thickness of 0,10-2 meters. The fossils of this bed are dated to the Pliocene (4 to 4,5 million years old). For example, it contained Nyanzachoerus kanamensis, Loxodonta nyanzae, Deinotherium bozasi, Hippopotamus cf. imaguncula, Hipparion, Rhinocerotids, Bovids and Limicolaria. Bed 1 has the highest amount of recovered and found fossils of the site. , and because of this the fossil assemblage will be dominated by Pliocene taxa. It is interpreted as a beach deposit because to the south it merges into a lacustrine sediment. Because of weathering and erosion, a lot of fossils were moved to the gullies that are currently present.

Above the Homa agglomerate formation lies the Rawi formation (it is not exposed in the Kanam West gully). The fossils of this formation are from the Pleistocene. The researchers doubt that fossils from this formation could have ended up in the Kanam West Gully. The fossils that where recovered include Cercopithecoides kimeui, Giraffa jumae, a skeleton of the rhinoceros Ceratotherium simum, a cranium and mandible of Metridiochoerus andrewsi, remains of Hippopotamus gorgops and Hexaprotodon imagunculus. Above this layer there are four beds (A1-A4) that are assigned to the Apoko formation and are around two meters thick. This formation contains a lot of recent alluvium that was deposited on top of the formation. These beds have intruded all underlying strata, and in these cases, they can go up to ten meters thick. The mammalian fossils of these strata indicate that the beds were deposited during the late Pleistocene. There have also been found human fossils and lithic material culture that was identified as presumably middle stone age to late stone age. In these beds they also detected fauna, that was found in a circle around the supposed location of the Kanam mandible according to Leakey and Kent. Among this fauna were bovids such as Redunca reducna. Most of this fauna would have eroded from bed A1 and A3.

Paleoanthropology and Kanam mandible controversy
Based on the faunal assemblage it can be concluded there was a presence lacustrine, but also terrestrial and sub-arial fossils, this suggests a variable ecosystem. The researchers Pickford and Bassett collected in situ fossils from each bed and made notes on the preservation characteristics. Based on these they tried to link the provenance (which bed they came from) of the fossils to the characteristics of preservation. They looked at the concretions or sediment that covered the fossils. This was successfully done at Kanjera and now they tried it for Kanam-West. The fossils from some beds had unique coatings by which they could be identified. A big problem however was that some artifacts had no coating. But based on the preservation and the surface appearance, it is believed that the Kanam mandible was originally fossilized in bed A3. Most of the artefact of Kanam appear in bed 1 and 2 of the Apoko formation, but it is possible that the pebble tool Leakey found in association with the Kanam mandible had eroded from the beds A1 and A2. For example a lot of microliths are present on the surface of bed A3 where bed A4 is eroding away. Future fieldwork at the site might give more clarity on the controversy of the Kanam Mandible and new test pits at the site might make it possible to avoid problems associated with erosion.

References:
Bishop L.C., Plummer T.W., et al., 2022. Fauna and Paleoenvironments of the Homa Peninsula, Western Kenya, In: Reynolds S.C., Bobe R., (eds.), African Paleoecology and human evolution Human, Cambridge University Press and Assessment, 360-375.

Pickford M., 1987. The Geology and Palaeontology of the Kanam Erosion Gullies (Kenya), Mainzer Geowissenschaftliche Mitteilungen 16, 209-226.

Pickford M., 1984. Chapter 11 Area X: Homa Peninsula, In: Pickford M., (ed.), Kenya Paleontology Gazetteer volume 1, National Museums of Kenya department of sites and Monuments Documentation 205-230.