Contracting eastern African C(4) grasslands during the extinction of Paranthropus boisei

The extinction of the Paranthropus boisei estimated to just before 1 Ma occurred when C(4) grasslands dominated landscapes of the Eastern African Rift System (EARS). P. boisei has been characterized as an herbivorous C(4) specialist, and paradoxically, its demise coincided with habitats favorable to its dietary ecology. Here we report new pedogenic carbonate stable carbon (δ(13)C(PC)) and oxygen (δ(18)O(PC)) 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 δ(13)C(PC) values from the EARS dated to 3–0 Ma, conducted time-series analysis of woody cover (ƒ(WC)), and compared the EARS ƒ(WC) trends to regional and global paleo-environmental and -climatic datasets. Our results demonstrate that the long-term rise of C(4) grasslands was punctuated by a transient but significant increase in C(3) vegetation and warmer temperatures, coincident with the Mid-Pleistocene Transition (1.3–0.7 Ma) and implicating a short-term rise in pCO(2). The contraction of C(4) grasslands escalated dietary competition amongst the abundant C(4)-feeders, likely influencing P. boisei’s demise.