EXPLORING THE UTILITY OF CARBON ISOTOPE ANALYSES OF MICROMAMMAL TOOTH ENAMEL AS AN ENVIRONMENTAL PROXY

Carbon isotope analyses of tooth enamel have been widely employed by paleoanthropologists to understand past habitats. However, most such studies use large- to medium-bodied mammals, which maintain similar diets across heterogeneous environments diminishing their value as paleoenvironmental proxies. Even mixed-feeding taxa do not reliably record environmental characteristics (i.e. relative abundance of C₃ and C₄ vegetation) in their carbon isotope compositions. There is increasing interest in using micromammals to resolve questions about past environments as they are common in the fossil record, diverse in dietary/habitat preference, yet have limited lifespans and home range sizes. Micromammals therefore may provide paleohabitat information with higher resolution because the carbon isotope compositions of micromammal communities and/or species might reflect the relative percentages of C₃ and C₄ vegetation in local environments more accurately than larger-bodied species. To investigate this possibility we assessed the degree to which carbon isotope compositions of micromammal communities record spatial changes in habitat in a southern African savanna environment. Sampling sites were ranged from very open (~5% canopy cover) to wooded (~60% canopy cover). Our results suggest that micromammalian communities, on the whole, are relatively poor indicators of the relative abundance of C₃ and C₄ vegetation in local environments, although some individual taxa that show promise in this regard. To complement this modern study, we performed isotopic analysis of the enamel of fossil micromammals from the hominin sites in the Cradle of Humankind, South Africa. On balance, the carbon isotopic dataset suggests that Australopithecus and Paranthropus were associated with more grassy environments than are found in the area today.