SEASONAL AND INTERANNUAL VARIATION IN THE DIETS OF TURKANA BASIN HOMININS, THEROPITHECUS, AND OTHER MAMMALS

The well-documented expansion of C₄ vegetation in the Turkana Basin and elsewhere in eastern Africa since the Pliocene is accompanied by increasing consumption of C₄-based foods by members of at least 4 mammalian orders, including Primates (hominins and Theropithecus). Prior isotopic studies of dietary change have relied on bulk tooth enamel measurements that reveal interspecific and interindividual variation but mask short-term changes that are important for understanding how individuals respond to environmental change. We investigate individual-level diet breadth of Turkana Basin fossil hominins (n = 25) and Theropithecus (n = 15) using laser ablation isotopic analysis. We find significant intratooth carbon isotope variability among specimens of most hominin taxa and Theropithecus, indicating marked shifts in the diets of individuals across seasons and years. We explore possible drivers of individual diet variation and discuss the contribution of intratooth records to studies of long-term dietary change, previously understood through point estimations of bulk diet. Finally, as a comparison we discuss intratooth carbon isotope variability in other mammalian taxa in the Turkana Basin, including browsing and mixed-feeding non-Theropithecus cercopithecids (n = 6) and ruminants (n = 3) analyzed using laser ablation as well as C₄ grazing equids (n = 10) analyzed using conventional methods. Ongoing isotopic studies of intratooth variation among fossil mammals in the Turkana Basin and elsewhere will be important for understanding the how mammal lineages respond to climatic and vegetation change. The ecology of fossil mammals must be understood in the context of seasonal-scale diet variability, which can influence selective pressures associated with resource availability, nutritional balance and competitive interactions.