Stable Isotopic Analyses of Laetoli Fossil Herbivores

In order to further refine early hominin paleoecology at Laetoli, over 500 specimens of fossil enamel and ostrich eggshell fragments collected from the Laetolil Beds and the Upper Ndolanya Beds were analyzed isotopically. The goal was to develop a high-resolution spatio-temporal framework for identifying and characterizing foraging patterns of mammalian herbivore lineages and fossil ostriches that could be used to investigate aspects of plant physiognomy and climate through the Laetoli succession. In general, dietary patterns at Laetoli suggest heterogeneous ecosystems with both C3 and C4 dietary plants available that could support grassland, woodland, and forested communities. All large-bodied mammalian herbivores analyzed yielded dietary signatures indicating mixed grazing/browsing strategies or exclusive reliance on C3 browse, more consistent with wooded than grassland-savanna biomes. Although there were no obvious uniform dietary shifts within specific mammalian herbivore groups in the sequence, the transition from the Upper Laetolil Beds to the Upper Ndolanya Beds documents a significant increase in the representation of grazing bovids. Relative to extant taxa in related lineages, the isotopic ranges of a number of Laetoli fossil herbivores are anomalous, indicating significantly more generalized intermediate C3/C4 feeding behaviors, perhaps indicative of dietary niches and habitat types with no close modern analogs. Diets of ostriches as reflected in the isotopic composition of eggshell components indicate predominantly C3 diets but with discrete isotopic shifts within the sequence linked to taxonomic and possibly environmental change.