Tendances environnementales en Afrique de l’Est au Plio-Pléistocène : étude des isotopes stables de carbone et d’oxygène de l’émail des herbivores
The Awash Valley, the Turkana Basin and the lower Omo Valley of East Africa, rich in hominins, are three regions that have been particularly important in paleoanthropology for documenting our evolutionary history. The aim of this study is to better document the environmental context of hominins by analyzing herbivores’ enamel stable carbon and oxygen isotopic values of the fossil fauna of the lower Omo Valley, the Turkana Basins and the Awash Valley from 7.4 Ma to 10 Ka. Based on a compilation of published isotopic data, this approach allows us to compare aridity as well as changes in the proportion of woody plants (C3) and tropical grasses (C4). At 4.4 Ma, results show open settings at Aramis with presence of C3 vegetation in relatively mesic conditions. Thus, it is possible that Ardipithecus ramidus preferred a wooded biome in a somewhat open environment according to the carbon value of the ecosystem presented in this study. Also, results indicate a peak of a C3 diet toward 4 Ma in the Awash Valley and the Turkana Bassin that is coincident with a peak of aridity in both regions, suggesting the expansion of xeric C3 bushes. This signal of an increase of C3 biomass in xeric conditions, that coincide with the appearance of the firsts australopiths, reconciliate previous interpretations of a diet dominated by C3 plants while showing signs of an abrasive diet in Australopithecus anamensis. Moreover, data show that the lower Omo Valley is different from the other two regions in being particularly humid and indicate the presence of mesic C4 grasses after 3 Ma. In conclusion, results of this study suggest that precipitations do not always have the expected effect on changes in C3/C4 plants proportions.
Bassin Omo-Turkana Herbivores Awash Valley Omo-Turkana Basin Environment Hominins Diet Aridity