Aridity and hominin environments

TLDR

Aridification has long been viewed as a key driver of ecological change and hominin evolution in eastern Africa, but testing this hypothesis is hampered by challenges in reconstructing terrestrial paleoclimate, and other factors such as rainfall seasonality and plant‑mammal interactions may also shape C4 grass‑dominated biomes. The study aims to develop a revised aridity index that quantifies water deficit using tooth enamel δ18O values and apply it to assess paleoaridity over the past 4.4 million years in eastern Africa. The authors calculate water deficit from δ18O measurements in tooth enamel and use this index to evaluate terrestrial aridity across 4.4 million years of eastern African records.

Abstract

Aridification is often considered a major driver of long-term ecological change and hominin evolution in eastern Africa during the Plio-Pleistocene; however, this hypothesis remains inadequately tested owing to difficulties in reconstructing terrestrial paleoclimate. We present a revised aridity index for quantifying water deficit (WD) in terrestrial environments using tooth enamel δ18O values, and use this approach to address paleoaridity over the past 4.4 million years in eastern Africa. We find no long-term trend in WD, consistent with other terrestrial climate indicators in the Omo-Turkana Basin, and no relationship between paleoaridity and herbivore paleodiet structure among fossil collections meeting the criteria for WD estimation. Thus, we suggest that changes in the abundance of C4 grass and grazing herbivores in eastern Africa during the Pliocene and Pleistocene may have been decoupled from aridity. As in modern African ecosystems, other factors, such as rainfall seasonality or ecological interactions among plants and mammals, may be important for understanding the evolution of C4 grass- and grazer-dominated biomes.