What links a fossil finger bone and teeth found in a cave in Siberia's remote Altai Mountains to a single tooth found in a cave in the calcareous landscapes of tropical Laos? The answer to this question has been established by an international team of researchers from Laos, Europe, the United States and Australia.
The human tooth was found by chance during an archaeological investigation in a remote area of Laos. Scientists have shown that it comes from the same ancient human population first recognized in Denisova Cave in the Altai Mountains of Siberia.
The research team made the significant discovery during their 2018 excavation campaign in northern Laos. The new Tam Ngu Hao 2 cave, also known as Cobra Cave, is located near the famous Tam Pà Ling Cave, where another important 70,000-year-old human fossil (Homo sapiens) had previously been found.
International researchers are confident that the two ancient sites are related to the Denisovan occupations despite being thousands of kilometers apart.
Their findings have been published in Nature Communications , under the direction of the University of Copenhagen, the CNRS (France), the University of Illinois Urbanna-Champain (USA) and the Ministry of Information, Culture and Tourism of Laos, and with the support of the microarchaeological work carried out at Flinders University and geochronological analyzes from Macquarie University and Australia's Southern Cross University.
Lead author and University of Copenhagen Associate Professor of Paleoanthropology Fabrice Demeter says the cave sediments contained teeth from giant herbivores, ancient elephants and rhinos that were known to live in forested environments. After all this work following the numerous clues written about fossils from very different geographical areas, our findings are significant , says Professor Demeter.
This fossil represents the first discovery of Denisovans in Southeast Asia and demonstrates that Denisovans were in the south at least as far as Laos. This is consistent with genetic evidence found in current populations of Southeast Asia .
Following a very detailed analysis of the shape of this tooth, the research team identified many similarities to Denisovan teeth found on the Tibetan Plateau, the only other place where Denisovan fossils have been found. This suggested that it was probably a Denisovan that lived between 164,000 and 131,000 years ago in the hot tropics of northern Laos.
Associate Professor Mike Morley of Flinders University's Microarchaeology Laboratory says the cave site was found high up in limestone mountains and contains remnants of an ancient fossil-filled cemented cave sediment. This Denisovan tooth demonstrates that they were once present in the karst landscapes of Laos , says Professor Morley.
The complexity of the site posed a challenge for dating and required the involvement of two Australian teams. The Macquarie University team, led by Associate Professor Kira Westaway, was tasked with dating the cave sediments surrounding the fossils, and the Southern Cross University team, led by Associate Professor Renaud Joannes-Boyau , carried out the direct dating of the unearthed fossil remains.
Establishing a sedimentary context for the final resting place of the fossils provides an internal check on the integrity of the find:if the sediments and fossils yield a similar age, as seen in Tam Ngu Hao 2, then we know that the fossils were buried shortly after the death of the organism , says Professor Kira Westaway.
Direct dating of fossil remains is crucial if we want to understand the succession of events and species in the landscape. The good concordance of the different dating techniques, both in the sediments and in the fossils, attests to the quality of the chronology for the species of the region. And this has many implications for the mobility of populations across the landscape , says Professor Renaud Joannes-Boyau of Southern Cross University.
The fossils were likely scattered across the landscape when they were washed into the cave during a flood that deposited the sediments and fossils. Unfortunately, unlike the Denisova cave, the humid conditions of Laos prevented the preservation of ancient DNA. However, archaeologists found ancient proteins that suggest the fossil was a young human, probably female, between 3.5 and 8.5 years old.
The finding suggests that Southeast Asia was a hotspot of diversity for humans, with at least five different species camping out at different times:Homo erectus, the Denisovans/Neanderthals, Homo floresiensis, Homo luzonensis, and Homo sapiens.
The caves of Southeast Asia could provide the next clue and more compelling evidence to understand these complex demographic relationships.