Synergistic roles of climate warming and human occupation in Patagonian megafaunal extinctions during the Last Deglaciation

Abstract

The causes of Late Pleistocene megafaunal extinctions (60,000 to 11,650 years ago, hereafter 60 to 11.65 ka) remain contentious, with major phases coinciding with both human arrival and climate change around the world. The Americas provide a unique opportunity to disentangle these factors as human colonization took place over a narrow time frame (~15 to 14.6 ka) but during contrasting temperature trends across each continent. Unfortunately, limited data sets in South America have so far precluded detailed comparison. We analyze genetic and radiocarbon data from 89 and 71 Patagonian megafaunal bones, respectively, more than doubling the high-quality Pleistocene megafaunal radiocarbon data sets from the region. We identify a narrow megafaunal extinction phase 12,280 ± 110 years ago, some 1 to 3 thousand years after initial human presence in the area. Although humans arrived immediately prior to a cold phase, the Antarctic Cold Reversal stadial, megafaunal extinctions did not occur until the stadial finished and the subsequent warming phase commenced some 1 to 3 thousand years later. The increased resolution provided by the Patagonian material reveals that the sequence of climate and extinction events in North and South America were temporally inverted, but in both cases, megafaunal extinctions did not occur until human presence and climate warming coincided. Overall, metapopulation processes involving subpopulation connectivity on a continental scale appear to have been critical for megafaunal species survival of both climate change and human impacts.

Keywords: Antarctic Cold Reversal; PATAGONIA; Pleistocene; South America; climate; extinction; human occupation; megafauna; mitochondrial DNA; radiocarbon.

Fig. 1. Extinction chronology of Pleistocene megafauna in southern Patagonia (9000 to 18,000 years ago), shown against West Antarctic Ice Sheet Divide ice δ¹⁸O record (bottom) and the timing of Antarctic Cold Reversal chronozone (blue column) (9).

Calibrated radiocarbon (¹⁴C) ages of extinct megafaunal remains from Patagonia [open circles with 1σ uncertainty indicated by vertical whiskers] are shown with calculated Phase boundary start and end (extinction) estimates (filled red squares) using the Southern Hemisphere calibration (SHCal13) curve (51) and OxCal 4.2 (26). The vertical gray bar denotes the 1σ range for megafaunal extinction in Patagonia. Calibrated ¹⁴C ages for the arrival of humans (with Monte Verde shown as “MV” with dashed line for extended age range) and modern lineage of L. guanicoe are shown as open circles and red square. (Top) A summary of the Northern Hemisphere climate and North American megafaunal extinctions is also presented. The Greenland δ¹⁸O and isotope event stratigraphy are shown (GS, Greenland Stadial; GI, Greenland Interstadial) (60), with the summed probabilities (1σ) of the youngest ¹⁴C dates for the latest Pleistocene megafaunal extinctions in North America (27), using the IntCal13 calibration curve (59). The tan and blue shading highlights the inverted timing of warm and cold intervals in the Northern Hemisphere and Southern Hemisphere during the Last Termination. WAIS, West Antarctic Ice Sheet; NGRIP, North Greenland Ice-Core Project.

Fig. 2. Mitochondrial DNA phylogenies of Late Pleistocene Patagonian megafauna (red) relative to extant taxa (black).

(A) Phylogenetic reconstructions of ancient and modern camelid sequences revealed two groups of camelids: Lama gracilis and a distinct clade of L. guanicoe. (B) Pleistocene Panthera onca were distinct from modern jaguars and represent the extinct subspecies P. onca mesembrina. (C) In contrast, sequences from Pleistocene Puma concolor are closely related to modern haplotypes. All Pleistocene samples represent haplotypes that are extinct or unsampled in modern populations.