Timing of Quaternary megafaunal extinction in South America in relation to human arrival and climate change

Abstract

South America lost more genera in the Quaternary megafaunal extinction than any other continent, but how it fits into the worldwide extinction has been unclear largely due to the lack of chronological resolution. This work evaluated 138 published radiocarbon dates for megafauna and 402 published dates for early (>8000 BP) South American archaeological sites. A total of 93 megafauna dates for 15 genera, and 110 archaeological dates on early human appearance, are robust enough to assess correspondence between last-appearance records of megafauna, first-appearance records of humans, and the Younger Dryas to Holocene climatic transition in six different regions of South America. Interesting patterns come to light, but are based on few dates, particularly in northern South America. No taxon other than Mylodon has >7 robust dates, and many taxa have less than 3 dates. Accordingly, an assessment of how likely it is that only a few dates will yield the youngest date in an underlying frequency distribution of dates was conducted, by applying probability and bootstrapping analyses to 27 dates on Mylodon from southern Patagonia, 26 of them from a single site. It was found that 15 dates out of a sample of 27 will commonly yield a date within 200 years of the youngest date in the sample. For that reason, and because even for a taxon with many dates it is likely that the youngest dated specimen pre-dates the actual time of extinction, most of the last-appearance dates are interpreted as recording the last time taxa were abundant on the landscape, rather than extinction per se. With those caveats in mind, on a continental scale most megafauna have last appearances after human arrival, but seem to last at least 1000 years after first human presence. Some taxa apparently survived >6000 years after humans entered South America and >1000 years after the end-Pleistocene climatic changes. Last-appearance patterns for megafauna differ from region to region, but in Patagonia, the Argentine and Uruguayan Pampas, and Brazil, extinctions seem more common after humans arrive and during intensified climatic change between 11.2 and 13.5 ka. This pattern suggests that a synergy of human impacts and rapid climate change—analogous to what is happening today—may enhance extinction probability. Nevertheless, even in these regions, some megafauna persisted for thousands of years after human arrival and after the climate warmed. These results highlight the need for future intensive dating efforts on South American megafauna and archaeological remains.