Contracting eastern African C4 grasslands during the extinction of Paranthropus boisei

Rhonda L Quinn,Christopher J Lepre

doi:10.1038/s41598-021-86642-z

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.

Highlights

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)
More recent archaeological evidence suggests that both Homo and Paranthropus were plausible inheritors of tool-making b ehaviors[4,5], and stable carbon isotopic (δ13Cenamel) and microwear analyses of fossil specimens have revealed a dynamic and complex evolutionary history of Pleistocene African hominin and non-hominin primate diets (Fig. 1)[6,7,8,9,10,11,12,13]
Exponential (Fig. 3A) and Loess (Fig. 3B) smoothing of the compiled EARS ƒWC record from 3 to 0 Ma illustrate the long-term increase in C4 vegetation punctuated by a short-term increase in C 3 vegetation beginning at the start of the Mid-Pleistocene Transition (MPT) interval and peaking at 1 Ma

Summary

Introduction

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’s extinction, estimated between 1.3 Ma14 and just prior to 1 Ma18, occurs during one of Homo’s significant increases in brain size and its second wave of dispersal out of Africa and into E urasia[19,20] These evolutionary events in the hominin lineage are coincident with the Mid-Pleistocene Transition (MPT; 1.3–0.7 Ma)[21], when the Earth’s glacial and interglacial climatic. During the MPT interval, current environmental proxy records from the East African Rift System (EARS) show evidence for low percentages of woody cover[24] and high abundances of C4-feeders[26,27,28,29] This scenario begs the question: why would P. boisei, this “durable” herbivorous C 4-feeding hominin, disappear during the dominance of C 4 grasslands?

Methods

Results

Conclusion