Contracting eastern African C4 grasslands during the extinction of Paranthropus boisei

Abstract

The extinction of the Paranthropus boisei estimated to just before 1 Ma occurred when C4 grasslands dominated landscapes of the Eastern African Rift System (EARS). P. boisei has been characterized as an herbivorous C4 specialist, and paradoxically, its demise coincided with habitats favorable to its dietary ecology. Here we report new pedogenic carbonate stable carbon (δ13CPC) and oxygen (δ18OPC) values (nodules = 53, analyses = 95) from an under-sampled interval (1.4–0.7 Ma) in the Turkana Basin (Kenya), one of the most fossiliferous locales of P. boisei. We combined our new results with published δ13CPC values from the EARS dated to 3–0 Ma, conducted time-series analysis of woody cover (ƒWC), and compared the EARS ƒWC trends to regional and global paleo-environmental and -climatic datasets. Our results demonstrate that the long-term rise of C4 grasslands was punctuated by a transient but significant increase in C3 vegetation and warmer temperatures, coincident with the Mid-Pleistocene Transition (1.3–0.7 Ma) and implicating a short-term rise in pCO2. The contraction of C4 grasslands escalated dietary competition amongst the abundant C4-feeders, likely influencing P. boisei’s demise.

Disruption of trait-environment relationships in African megafauna occurred in the middle Pleistocene

“…In our ecometric approach, we evaluated the relationship of community-level body mass, hypsodonty, and loph count with the fractions of woody cover that occur within communities. We considered woody cover as our environmental variable for several reasons: (1) it is a strong proxy of the composition of vegetation across eastern African sites, as it signifies the degree to which sites are composed of trees or grasses; 53 , 166 (2) it is a more reliable representative of late-Cenozoic grassland expansion in eastern Africa than other environmental variables, like temperature and precipitation; 81 , 167 and (3) the woody cover data at the fossil and modern sites in our dataset are of high quality 142 , 149 . Body mass is fundamentally related to woody cover because of its role in optimizing nutrient acquisition from vegetation types of different nutritive quality 127 .…”

Southern Hemisphere Subtropical Front impacts on Southern African Hydroclimate and early Hominins Across the Mid-Pleistocene Transition

“…Species that could not adapt or migrate may have perished; this may be particularly true for members of the genus Paranthropus. P. boisei, which likely had a specialized C 4 diet [52,53], went extinct sometime between 1.3 and 1 Ma -during the interval when the WRZ expanded and proxy evidence suggests the Eastern African C 4 grasslands contracted [53]. In contrast, P. robustsus, whose diet appeared to largely consist of C 3 vegetation (e.g.…”