The Incorporation of C4 Plants Into Hominin and Baboon Diets During the Early Pliocene Neogene

Dietary change among hominins and cercopithecids in Ethiopia during the early Pliocene

Authors:

Levin et al

Abstract:

The incorporation of C4 resources into hominin diet signifies increased dietary breadth within hominins and divergence from the dietary patterns of other great apes. Morphological evidence indicates that hominin diet became increasingly diverse by 4.2 million years ago but may not have included large proportions of C4 foods until 800 thousand years later, given the available isotopic evidence. Here we use carbon isotope data from early to mid Pliocene hominin and cercopithecid fossils from Woranso-Mille (central Afar, Ethiopia) to constrain the timing of this dietary change and its ecological context. We show that both hominins and some papionins expanded their diets to include C4 resources as early as 3.76 Ma. Among hominins, this dietary expansion postdates the major dentognathic morphological changes that distinguish Australopithecus from Ardipithecus, but it occurs amid a continuum of adaptations to diets of tougher, harder foods and to committed terrestrial bipedality. In contrast, carbon isotope data from cercopithecids indicate that C4-dominated diets of the earliest members of the Theropithecus oswaldi lineage preceded the dental specialization for grazing but occurred after they were fully terrestrial. The combined data indicate that the inclusion of C4 foods in hominin diet occurred as part of broader ecological changes in African primate communities.

C4 Grasses Spread Into North America Much Later Than South America or Europe

Spatiotemporal variation in the origin of C4 grasses: δ13C analysis of grass pollen from the southeastern United States

Authors:

Nelson et al

Abstract:

The C4-plant functional type is a major evolutionary and ecological success. However, the relative importance of environmental factors, such as climatic conditions and atmospheric CO2 concentrations, in driving the origin of C4 grasses in different parts of the world remains poorly understood. We determined the carbon-isotope composition of 612 individual grains of grass pollen in seven sediment samples from the southeastern United States from the middle/late Eocene. By applying a Bayesian model to these data, we determined the probability of rejecting (at p < 0.05) the null model that each sample contained pollen from only C3 grasses. We could not reject the null hypothesis for any sample when using a range of potential values of δ13C of atmospheric CO2. These results suggest that C4 grasses were not present on the landscape during the middle/late Eocene, a conclusion consistent with a limited number of studies from more northern and western regions of North America. In contrast, prior studies indicate that C4 grasses existed during this time in parts of Europe and South America. Together these results imply variations in the location, time, and environmental conditions associated with the origin of C4 grasses.