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

Analysis of enamel stable carbon isotopes (δ¹³C_enamel) 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 δ¹³C_enamel of herbivores and ecosystem vegetation structure has not been rigorously established. Here we combine δ¹³C_enamel 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 δ¹³C_enamel 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 δ¹³C_enamel values reflects changes in the relative abundance of C₃-C₄ vegetation. We conclude that analyses using herbivore δ¹³C_enamel data to shed light on the environmental context of hominin evolution should look to explicitly community-level approaches for making vegetation inferences.