Late Pleistocene South American megafaunal extinctions associated with rise of Fishtail points and human population

The late Pleistocene witnessed widespread megafaunal extinctions globally, except in Africa. The causes remain debated, with hypotheses including climate change, disease, habitat alteration, and human hunting. In the Americas, extinctions coincided with both significant climatic shifts and the arrival of humans, making causal attribution complex. While the "Pleistocene overkill" hypothesis, positing human hunting as the primary cause, is strongly debated in North America, its role in South America is less considered. This study aims to evaluate the relative importance of human predation in South American megafaunal extinctions using a comprehensive analysis of the temporal and spatial distributions of megafaunal remains and FPP, the most abundant and widely distributed early projectile points in South America. The research questions center around the temporal relationship between human arrival/population growth, FPP technology adoption, and megafaunal decline. The hypothesis is that human predation played a significant role in the South American megafaunal extinctions.

Existing literature on Pleistocene extinctions in the Americas presents contrasting views. Some emphasize climate change as the primary driver, while others highlight the potential impact of human hunting, often focusing on the North American Clovis culture. In South America, the debate is less centered on human involvement, with FPP technology—chronologically later than Clovis—being linked to megafauna but lacking strong evidence of direct exploitation. The lack of a clear consensus necessitates a thorough investigation into the spatiotemporal dynamics of both megafauna and humans to establish the extent of human influence on South American extinctions. Previous studies have suggested that environmental changes alone cannot fully explain the extinctions, pointing to a potential synergistic role of both climatic shifts and human actions.

The study uses a combined temporal and spatial analysis to assess the relationship between megafauna, FPP, and human populations. Temporal analysis employed the Summed Probability Distribution (SCPD) method on radiocarbon dates for megafauna, FPP, and archaeological sites across South America, focusing on three regions with strong evidence of human-megafauna interaction: Pampa, Southern Patagonia, and the Andes. This approach helps to determine the relative densities of megafauna and FPP throughout time. Spatial analysis used Species Distribution Modeling (SDM) with MaxEnt to estimate the potential distributions of megafauna (species with evidence of association with humans) and FPP between 18,000 and 9,000 years BP using bioclimatic variables. The overlap between these distributions was quantified using a similarity index to determine the degree of co-occurrence. This helps visualize the geographic relationship between human activity and megafaunal populations. The authors also compared the temporal patterns of megafauna and FPP density with variations in human population density, based on available archaeological radiocarbon dates. The combined temporal and spatial analyses allowed for a robust assessment of the relationship between human activities and the observed megafaunal extinctions.

The SCPD analysis revealed a significant increase in megafaunal density around 17,500 years BP, followed by a sharp decline beginning around 12,900 years BP. This decline coincided with the appearance and rapid expansion of FPP technology, and a peak in human population density between 12,400 and 12,200 years BP. The subsequent decline in both FPP and human population density further reinforced the temporal association. Spatial analysis, using SDM, indicated significant overlap between the potential distributions of megafauna and FPP, particularly in the Pampa and Patagonia regions, demonstrating geographic co-occurrence of humans and megafauna. Species with high distributional overlap with FPP suggest they were likely targets for human hunting. The Andes region showed a comparatively lower level of overlap. The analysis of niche overlap confirmed this spatial relationship, suggesting the FPP hunters mainly concentrated in open grassland environments of Pampa and Patagonia. Notably, the decline in megafaunal density does not align well with significant climatic changes, making human impact a significant explanation. The results showed a strong spatiotemporal correlation between the expansion of FPP technology, increase in human population density and the subsequent sharp decline in megafauna. The close correspondence between these phenomena supports the hypothesis that human hunting contributed significantly to the observed megafaunal extinctions.

The strong correlation between the rise of FPP technology, human population growth, and the subsequent decline of megafauna strongly suggests that human predation played a significant role in the late Pleistocene extinctions in South America. While the limited archaeological evidence of direct megafaunal exploitation may seem contradictory, the results suggest that even moderate human predation on a few key species could have cascading effects on the entire megafaunal community, particularly given the vulnerability of large mammals to environmental changes. The temporal mismatch between major climate shifts and the megafaunal decline further supports the hypothesis that human hunting was a significant driver. The study’s findings suggest a more nuanced view than a simple dichotomy of climate change versus human impact, highlighting a potential synergistic effect where human hunting exacerbated the impact of existing environmental pressures. These results challenge the prevailing assumption of a minor human role in South American megafaunal extinctions.

This study provides strong evidence for a significant role of human predation, particularly associated with FPP technology, in the late Pleistocene megafaunal extinctions of South America. The close spatiotemporal correlation between the spread of FPP technology, human population increase, and the decline of megafauna strongly suggests a causal link. Future research could focus on more detailed species-specific analyses to refine our understanding of the relative impact of human predation on individual megafaunal species and further explore the complex interplay of environmental and anthropogenic factors driving the extinctions.

The study relies on available radiocarbon dates and fossil records, which may be incomplete or biased. Taphonomic processes and preservation challenges can influence the availability and interpretation of both megafaunal remains and archaeological artifacts. Further, the study focuses on FPP technology, acknowledging that other hunting technologies might have also played a role. The limited direct evidence of human predation on all extinct species presents a limitation in definitively proving direct causality but doesn't negate the overwhelming statistical correlation of human arrival and megafaunal decline.