Intrataxonomic trends in herbivore enamel δ13C are decoupled from ecosystem woody cover.

Analysis of enamel stable carbon isotopes (δ13Cenamel) of fossil herbivores is an important tool for making inferences about Plio-Pleistocene vegetation structure in Africa and the environmental context of hominin evolution. Many palaeoecological studies implicitly or explicitly assume that individual variation in C3-C4 plant consumption among fossil herbivores directly reflects the abundance of C3 (trees, shrubs) or C4 (low-altitude tropical grasses) vegetation. However, a strong link between δ13Cenamel of herbivores and ecosystem vegetation structure has not been rigorously established. Here we combine δ13Cenamel data from a large dataset (n = 1,643) with multidecadal Landsat estimates of C3 woody cover across 30 African ecosystems to show that there is little relationship between intrataxonomic variation in δ13Cenamel and vegetation structure. This is especially true when removing forested ecosystems (>80% woody cover)-which numerous lines of evidence suggest are rare in the Plio-Pleistocene fossil record of eastern Africa-from our analyses. Our findings stand in contrast with the common assumption that variation in herbivore δ13Cenamel values reflects changes in the relative abundance of C3-C4 vegetation. We conclude that analyses using herbivore δ13Cenamel data to shed light on the environmental context of hominin evolution should look to explicitly community-level approaches for making vegetation inferences.