Mobilité altitudinale des pasteurs néolithiques dans la vallée du Rift (Kenya) : premiers indices de l'analyse du δ13C de l'émail dentaire du cheptel domestique

Neolithic sites in the Central Rift Valley of Kenya cover a wide altitudinal range, from the floor of the lake Nakuru-Elmenteita and Naivasha basins up to the top of the Mau Escarpment and Mount Eburu. Occupation of rockshelter sites located in various environments, from savanna to forest raises the question of landscape exploitation by Neolithic people. Analogy with modern and historic East African food producing societies suggests that the Neolithic pastoral communities could have practiced seasonal mobility between high and low pasture areas. Altitudinal mobility of herds is investigated using stable isotope analysis in teeth. Changing climatic conditions with altitude is accompanied by changes in the relative proportion of C3 and C4 plants. Because C3 and C4 plants have different carbon isotope ratios, a change in the C3/C4 plant proportion in diet is recorded in tooth enamel 13C/12C. This method is tested on modern animal teeth collected from Maasai herders, then applied to archaeological remains from Eburu Station Lava Tube Cave, Maasai Gorge, Enkapune Ya Muto and Enkapune Ya Sauli rock shelters. Results suggest that cattle were herded mainly in the floor of the Rift Valley, while more diverse settings are observed for caprines, which were herded both in low and middle elevation environments. No evidence was found for altitudinal mobility, or for exploitation of the high elevation mountain grasslands. These first conclusions must be considered with caution due to the small number of individuals analyzed, the bias introduced by high food selectivity by cattle, and some uncertainty in the interpretation of δ13C values in terms of altitude. Altitudinal mobility of Neolithic herders in the Central Rift Valley (Kenya): First evidence from δ13C analysis from domestic animals teeth Neolithic sites in the Central Rift Valley of Kenya cover a wide altitudinal range, from the floor of the lake Nakuru-Elmenteita and Naivasha basins up to the top of the Mau Escarpment and Mount Eburu. Occupation of rockshelter sites located in various environments, from savanna to forest raises the question of landscape exploitation by Neolithic people. Analogy with modern and historic East African food producing societies suggests that the Neolithic pastoral communities could have practiced seasonal mobility between high and low pasture areas. Altitudinal mobility of herds is investigated using stable isotope analysis in teeth. Changing climatic conditions with altitude is accompanied by changes in the relative proportion of C3 and C4 plants. Because C3 and C4 plants have different carbon isotope ratios, a change in the C3/C4 plant proportion in diet is recorded in tooth enamel 13C/12C. This method is tested on modern animal teeth collected from Maasai herders, then applied to archaeological remains from Eburu Station Lava Tube Cave, Maasai Gorge, Enkapune Ya Muto and Enkapune Ya Sauli rock shelters. Results suggest that cattle were herded mainly in the floor of the Rift Valley, while more diverse settings are observed for caprines, which were herded both in low and middle elevation environments. No evidence was found for altitudinal mobility, or for exploitation of the high elevation mountain grasslands. These first conclusions must be considered with caution due to the small number of individuals analyzed, the bias introduced by high food selectivity by cattle, and some uncertainty in the interpretation of δ13C values in terms of altitude.