Denisovans are a sister species of modern humans, inhabiting Laos between 164,000 and 131,000 years ago, and have had a significant impact on populations outside Of Africa and Australia. What would be associated with a finger bone and some fossil teeth found in a cave in a remote Altai Mountains in Siberia with a tooth found in a cave in a limestone landscape of tropical Laos? An international team of researchers from Laos, Europe, the United States and Australia has identified the answer to this question.
The human tooth was discovered by chance during an archaeological survey in a remote part of Laos. Scientists have shown that it comes from the same ancient human group first identified in denisova caves in the Altai Mountains of Siberia, known as the Denisovans.
The research team made this major discovery during a 2018 excavation in northern Laos. The new cave, Tam Ngu Hao 2, also known as the "Cobra" Cave, is located near the famous Tam Pà Ling Cave, where archaeologists have previously found another 70,000-year-old fossil of an important human (Homo sapiens).
An international team of scientists is convinced that the two ancient sites are related to the Denisovans, albeit thousands of miles apart.
Their findings, published in Nature Communications, were led by the University of Copenhagen (Denmark), the French National Centre for Scientific Research (CNRS), the University of Illinois at Urbana-Champaign (USA), the Lao Ministry of Information, Culture and Tourism, and supported by microarchaeological work by Flinders University (Australia) and geochronological analysis at Macquarie University and Southern Cross University in Australia.
Lead author Fabrice Demeter, associate professor of paleoanthropology at the University of Copenhagen, said the cave sediments contained the teeth of giant herbivores, ancient elephants and rhinos, which are known to live in woodland environments.
"After all this work, following the many clues written on fossils from very different geographical regions, our findings make sense," Professor Demeter said.
"This fossil represents the first discovery of Denisovans in Southeast Asia and suggests that Denisovans have been to Laos at least in the south." This is consistent with the genetic evidence found in modern Southeast Asian populations. ”
After a very detailed analysis of the shape of the tooth, the team found that it bore many similarities to the Denisovar teeth found on the Tibetan Plateau — the only other place where Denisovan fossils were found.
This suggests that it is likely to be a Denisovan who lived in the warm tropical regions of northern Laos between 164,000 and 131,000 years ago.
Mike Morley, an associate professor from Flinders University's Microarchaeology Laboratory, said the cave site, called Tam Ngu Hao 2 (Cobra Cave), was found high up on a limestone mountain with remnants of an ancient cemented cave sediment filled with fossils.
"We basically found unmistakable evidence of the crime — this Denisovan tooth shows that they once appeared in the karst landscape of Laos so far south," Morley said. ”
The complexity of the site created challenges for the mapping work, which required two Australian teams to complete.
The Macquarie University team, led by Associate Professor Kira Westaway, provided dating of cave sediments around the fossils, while the Southern Cross University team, led by Associate Professor Renaud Joannes-Boyau, conducted direct dating of the excavated fossil remains.
Kira Westaway said: "Establishing a sedimentary background for the final resting place of fossils allows for an internal check of the integrity of the findings – if the sediments and fossils are similar in age, as seen in Tam Ngu Hao 2, then we know that the fossils were buried shortly after the organism died." ”
If we want to understand the evolution of events and species in the landscape, it is crucial to directly measure the fossil remains.
"The good consistency of different dating techniques on sediments and fossils is evidence of the quality of the chronology of species in this area." Professor Renaud Joannes-Boyau of Southern Cross University said: "This has a big impact on the movement of people in the landscape. ”
The fossils were most likely scattered on the surface during a flood event that precipitated sediment and fossils during a flood event.
Unfortunately, unlike Denisova Cave, the humid conditions of Laos mean that ancient DNA has not been preserved. However, archaeologists did find ancient proteins, suggesting that the fossil was a young, possibly female human, perhaps between the ages of 3.5-8.5 years.
The finding suggests that Southeast Asia is a hotspot for human diversity, with at least five different species camping at different times; Homo erectus, Denisovans/Neanderthals, Floresians, Luzonians, and Homo sapiens.
Caves in Southeast Asia can provide the next clue and further conclusive evidence to understand these complex demographic relationships.