Extinctions in North America’s Late Glacial landscapes

Abstract

Human-caused extinctions of terrestrial mammals in large parts of the world such as North America may have been side-effects of rapid long-distance dispersals (biogeographic range-change) by Homo sapiens moving outward from the Old World. The extinctions help explain how modern humans briskly explored and populated large, empty, and increasingly unfamiliar landmasses. Infrequent opportunistic human hunting along with the climate-caused fragmentation of megafaunal populations may have led to nonrandom human dispersals through megafaunal ‘source’ areas, which effectively were continental stepping-stones, resulting in temporally clustered extinctions. The process in North America was three-step, and mostly occurred before the Younger Dryas cold interval: first was a foreshock, when Late Glacial climatic changes and a trickle of first foragers fragmented continental megafaunal populations; second was a severe additional shock when human foragers targeted the pockets of fragmented subpopulations and preferentially hunted them; and third was an extended aftershock of sustained hunting, inbreeding damage, and acute competition for contracting resources during which megafaunal taxa dwindled and became extinct. Some taxa may have managed to survive into the Younger Dryas or beyond. If there were pre-Clovis people in the continent, the second (shock) phase may have preceded Clovis (perhaps by up to a millennium), but by the time of the third (aftershock) phase the Clovis dispersal was rapidly underway.