The extinction of the Pleistocene megafauna at the end of the last ice age initiated the 6th great extinction. Determining whether humans or climatic factors caused the population collapse is actively debated. In South America one of the regions that is known to have supported both megafauna and relatively early human settlers is the Lagoa Santa District of southern Brazil. Caves in the Lagoa Santa region provide mixed assemblages of megafauna and human remains. What is uncertain is the extent to which the megafauna interacted or overlapped temporally with humans. I present the first paleoecological record from lowland South America that tracks the decline of megafauna and the ecological implications of the extinction event. In this study we investigate (1) if the decline of Sporormiella spores in the fossil records happened before or was coincident with the first records of human occupation in the Lagoa Santa region; (2) if the decline of Sporormiella spores was coincident with substantial changes in fossil pollen spectra, and (3) if there is an association of Sporormiella decline with changes in fire frequency. We recovered two long sediment records from the Lagoa Santa region using a Colinvaux–Vohnout coring rig. The cores were radiocarbon dated and analyzed for their fossil pollen, charcoal, and Sporormiella content. Standard palynological procedures were applied to the preparation of the samples.
Results/Conclusions
Our data showed that the decline of Sporormiella abundance, indicating the major megafaunal population collapse took place c. 13,500 years ago, while the oldest human record for the Lagoa Santa region is from c. 11,500 - 12,000 years ago. Our data clearly indicated that the major shift in megafaunal populations occurred 1500-2000 years before the arrival of humans in the region. Our data were highly consistent with parallel studies carried out in North America and, like those studies, we found that the decline of Sporormiella was followed by a marked increase in the abundance of charcoal particles and the establishment of non-analog floras. These notable changes in the fossil record are suggested to be the response of vegetation to rapid climate change and a release from herbivory. We cannot tell from these data whether any of the megaherbivore species went extinct prior to human arrival, although that is entirely possible. We consider it highly probable that humans entering the region induced the final wave of megafaunal extinctions, though they were not responsible for the initial population collapse.