QUANTIFYING LARGE MAMMAL EXTINCTION RATES AND SIZE-SELECTIVITY IN EASTERN AFRICA: A TEST OF ANCIENT ANTHROPOGENIC EXTINCTION HYPOTHESES

Abstract

A fundamental focus of paleoanthropology is understanding the impact of ancient humans ontheir ecosystems. One critical way that humans change their ecosystems is by driving other species to extinction, and researchers have recently argued that this process began with the appearance of Homo erectus. These researchers hypothesize that with novel adaptations such as increased brain size, heightened carnivory, and innovative technology, H. erectus preferentially drove large mammals to extinction (i.e., size-selectivity) as early as ~2 million years ago (Ma). Size-selectivity of mammal extinctions in Plio-Pleistocene Africa has been examined previously, but no study has done so while adequately accounting for incomplete preservation and sampling in the fossil record. Here, we analyzed a published presence-absence dataset of mammal species from eastern Africa over the last six million years. We used capture-mark-recapture methods to estimate time-varying extinction rates as a function of body size, while controlling for size- biased sampling. This model allows for the quantification of size-selective extinctions through time and for a test of the hypothesis that elevated size-selectivity emerged with the appearance of H. erectus at 2 Ma. We found no increase in size-selective extinctions of large mammals at or after 2 Ma, and thus our results do not support the hypothesis that H. erectus drove size-selective extinctions in eastern Africa during the Plio-Pleistocene.