The extinction of the so-called megafauna in South America that occurred about 11,000 years ago has been the subject of endless debate. Two factors are usually mentioned as possible causes of the disappearance of giant land sloths, mastodons, glyptodons (ancestors of today’s armadillo) and other animals that may have weighed tons: climate change, which is said to have made it impossible for them to adapt to a changing natural environment, and the arrival of modern man in their habitat. A study published August 18, 2017 in the scientific journal Quaternary Research employs an alternative methodology to address that question in Lagoa Santa, in Minas Gerais State, where there are prehistoric sites that attest to the presence of both humans and megafauna.
Brazilian biologist Marco F. Raczka, a postdoctoral researcher at Florida Technological Institute, in the United States, has analyzed the presence of fossilized vestiges of fungi of the genus Sporormiella, which serve as markers for the existence of large herbivores in a given area. Although the region may also be home to carnivores at the top of the food chain, such as the saber-toothed tiger, what is referred to as megafauna was composed, basically, of herbivores. “Our analyses indicate that the population of large herbivores was already declining in Lagoa Santa before humans arrived,” Raczka explains. “But their presence in the region probably helped accelerate the extinction process.” The article was co-signed by geologist Paulo Eduardo de Oliveira from the University of São Paulo (USP), and paleontologist Mark Bush, from Florida Tech.
Raczka collected vestiges of pollen, coal, and fungus from two bodies of water in the Minas region, Lagoa Olhos d’Água and Lago Mares, which formed around 23,000 years ago. The fungus reproduces in the intestinal tract of herbivores and is eliminated with the feces. Since the edges of lakes are places commonly chosen by animals answering the call of nature, those bodies of water area are where the fungus concentrated when there are (or were) herbivores nearby. According to the analyses, the quantity of the fungus in both lakes began to decline about 18,000 years ago, prior to the arrival of man in Lagoa Santa, and reached its lowest level between 12,000 and 11,000 years ago, by which time homo sapiens had put down roots there. The decline of the megafauna is believed to have begun during a colder and more humid period and their last days to have coincided with a moment of an increase in temperature. “The study does not intend to provide a definitive response about the extinction of megafauna,” Raczka points out. “We are simply applying a new kind of analysis to that question.” Sporormiella fungus has already been used in similar studies from Australia, the United States and Peru.
Bioanthropologist Walter Neves of USP, who studies the Lagoa Santa region, argues that the assumption that climate change or hunting would have led to the disappearance of megafauna does not make sense. “I don’t defend the environmental hypothesis because prior to their extinction those animals had resisted various climate fluctuations that were just as severe during the last three million years. Furthermore, there is not a single megafauna bone at the archaeological sites in Brazil, much less at Lagoa Santa, that would support the idea that excessive hunting took place,” Neves observes. “No one know why the megafauna vanished.”
RACZKA, M.F., BUSH, M.B., and OLIVEIRA, P.E. The collapse of megafaunal populations in southeastern Brazil. Quaternary Research, August 17, 2017.