Molecular dating has shown that several extinct creatures, such as giant sloths and mammoths, survived in South America much later than previously thought, raising questions about the root causes behind some of Earth鈥檚 most recent large animal extinctions.
鈥淭here is no consensus in the scientific community about the cause or causes that led to the extinction of megafauna in South America,鈥� says at the Federal University of Rio de Janeiro, Brazil.
South America was once home to many larger animals, including giant armadillos, elephants, sabre-toothed cats and sloths that weighed over 4 tonnes. It is widely thought that these animals went extinct shortly after the Pleistocene-Holocene boundary 11,700 years ago, when Earth鈥檚 climate got warmer and human populations started to expand around the world.
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鈥淭he emergence and global spread of behaviourally modern humans created pressures that many megafauna species could not withstand,鈥� says at Aarhus University in Denmark. Through hunting and possibly landscape modifications, humans dramatically reduced megafauna biodiversity around the world, he says.
But recent data shows that many extinctions occurred well after the arrival of these humans, says Cortes. In the Americas, they coexisted with megafauna for many thousands of years. This overlap, combined with the survival of heavily hunted species like deer, led Cortes and his team to pursue alternatives to the human-driven extinction hypothesis.
The researchers used radiocarbon dating to ascertain the ages of teeth from eight previously undated Brazilian specimens, including Smilodon populator, a sabre-toothed cat; Notiomastodon platensis, a South American elephant; Eremotherium laurillardi, a behemoth-sized sloth; and Palaeolama major, a large, extinct llama.
The results showed that several of these species survived thousands of years beyond previous estimates, pushing their extinctions far past the first appearance of Homo sapiens in South America. Most of these animals were still alive around 6000 to 8000 years ago, but two species, Palaeolama major and the camel-like Xenorhinotherium bahiense, survived until 3500 years ago, making them the last known surviving megafauna of South America.
鈥淭he study clearly shows that the famous Pleistocene-Holocene extinction was a long-term process of diversity loss of the Pleistocene mammals,鈥� says team member , also at the Federal University of Rio de Janeiro.
Cortes鈥檚 team argues that South American extinctions were largely due to environmental factors. The Holocene brought changes in climate that expanded forests and contracted savannahs, which drastically reduced the habitat large animals needed to survive. While human hunting probably also contributed to the decline, it wasn鈥檛 the leading factor, says Cortes.
However, Svenning thinks the findings are consistent with the idea that pressures exerted by growing human populations caused the extinctions. While he agrees that environmental factors might have played a role at certain local levels, he argues that the new data fits well with recent findings showing that some megafauna survived into the Holocene in Asia.
鈥淭his paper suggests the interplay between human activities and climatic and environmental changes was critical in driving the demise of the megafauna,鈥� says at the University of Bristol, UK. 鈥淪o, while humans are not solely to blame, we鈥檙e not off the hook.鈥�
Journal of South American Earth Science
