For a long time, the overall consensus has been that mammalian megafauna – giant mammals that roamed the Earth in the past, including species like mammoths, giant sloths and sabertoothed tigers – went extinct at the start of the Holocene. This is our current geological epoch, which started around 11,700 years ago, at the end of the last major glacial age.

However, some recent studies have obtained fossil evidence that challenges this consensus. In particular, the discovery that woolly mammoths were still alive 4,000 years ago helped undermine this idea. Now researchers have found other megafauna specimens, including giant sloths and camel-like animals, that survived in South America up to around 3,500 years ago.

This evidence raises questions about what really led to the planet’s most recent large animal extinction while also showing that it was not a homogenous event.

The research was conducted by Fábio Henrique Cortes Faria, a geologist at the Federal University of Rio de Janeiro, Brazil, and colleagues. The team carbon dated fragments of teeth from different megafauna species found at two fossil sites in Brazil (one from a location in Itapipoca and one from the Rio Miranda valley). From among the eight specimens they dated, two teeth – one belonging to an extinct genus of American llama called Palaeolama major while the other came from a camel-like creature that had the nose of a tapir, called Xenorhinotherium bahiense – were found to be much younger than expected.

“The ages obtained demonstrate that the latest ages of megafauna appearance in Brazil are associated with the middle and late Holocene,” the authors write.

If these animals were alive in Brazil at this time, then they would have lived side-by-side with humans who arrived in South America sometime between 20,000 and 17,000 years ago. This suggests a much longer period of coexistence, which challenges existing interpretations of what caused their eventual extinction.

“In South America,” the authors explain, “the extinction of megafauna has been attributed to many causes, climate/environmental changes or even the synergy between these hypotheses.”

One particular explanation, known as the Overkill and Blitzkrieg theories, held that South America’s megafauna were directly impacted by human hunting and possibly landscape modification; however, the body of mounting evidence would suggest otherwise.

“The ages obtained in this analysis, together with archaeological evidence, demonstrate that the Overkill and Blitzkieg theories are not plausible explanations for the extinction of South American megafauna.”

Instead, it is possible that the extinction event was a much more drawn-out process, which did not occur at the same time in all places. It is possible that this region of Brazil was a kind of refuge for some megafauna species who lived longer than others.

“The study clearly shows that the famous Pleistocene-Holocene extinction was a long-term process of diversity loss of the Pleistocene mammals,” Ismar de Souza Carvalho, one of the researchers who worked on this study, told New Scientist.

The study is published in the Journal of South American Earth Sciences.