Contracting eastern African C₄ grasslands during the extinction of Paranthropus boisei

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 (δ¹³C_PC) and oxygen (δ¹⁸O_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 δ¹³C_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 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.