150,000-year-old human tooth is rare evidence of Denisovan extinction


Denisovan's presumed molar.

Denisovan’s presumed molar.
Photo: F. Demeter et al., 2022

Paleontologists in Laos have discovered an ancient molar that probably belonged to a young girl from Denisovan. The discovery is significant, because the Laotian cave in which the molar was found is now one of only three places known to house these enigmatic humans.

In addition to Siberia and the Tibetan Plateau, we can now add Laos to the painfully short list of places that gave way. fossils of an elusive human species known as the Denisovans. A team of paleontologists have found Denisovan’s presumed molar in Tam Ngu Hao 2 Cave in the Annamese Mountains of Laos. The molar dates from the Middle Pleistocene, and it is the first Denisovan fossil ever found in Southeast Asia. A paper detailing this discovery Iis published today in Nature Communications.

Laura Shackelford, a University of Illinois at Urbana-Champaign anthropologist and co-author of the new study, was thrilled to learn that the Denisovans, like their Neanderthal cousins, inhabited a variety of environments, some of which extremes.

The entrance to Tam Ngu Hao 2 Cave, also known as Cobra Cave.

The entrance to Tam Ngu Hao 2 Cave, also known as Cobra Cave.
Photo: F. Demeter et al., 2022

“Although we only have a few fossils representing Denisovans, this new fossil from Laos demonstrates that, much like modern humans, Denisovans were widespread and highly adaptable,” Shackelford explained in an email. “They lived in the cold arctic temperatures of Siberia, in the cold, [oxygen poor] the environment of the Tibetan plateau, and now we know that they also lived in the tropics of Southeast Asia.

What’s more, the new discovery “further attests” that Southeast Asia was “a diversity hotspot for the genus. Homo” during the middle to late Pleistocene, as scientists write in their study. So, in addition to the Denisovans, this part of the world was once home to H. erectusNeanderthals, H. floresiensis, H.luzonensisand H. sapiens.

That a Denisovan fossil was found in Laos is no huge surprise. Traces of Denisovan DNA have been detected in the genomes of modern populations in Southeast Asia and Oceania. the Ayta Magboukun– a Filipino ethnic group – have retained about 5% of their Denisovan ancestry, the highest of any human group in the world. Denisovans separated from Neanderthals between 200,000 and 390,000 years ago. They eventually died out, but not before interbreeding with modern humans. The Laotian molar is only the 10he Denisovan fossil to be discovered and the first outside Siberia and Tibet.

The Annamite Mountains contain an abundance of limestone caves. Each year, Shackelford and his colleagues send geologists to the area in hopes of finding places worthy of further paleontological investigation.

“In 2018, our geologists spent the morning surveying and returned to the site before lunch with their pockets full of sediment samples they had collected from a potential new site, what we now know as the Tam Ngu Hao 2 or Cobra Cave,” Shackelford said. me. “In these early samples, among fragments of fossil animal teeth, we found the tooth.”

Dating the sediment in which the molar was found, the team aged the fossil to between 164,000 and 131,000 years old. Protein analysis of the tooth enamel identified the fossil as belonging to a member of the Homo genus, but this test did not identify the exact species.

Fabrice Demeter, co-author of the study, analyzes the molar.

Fabrice Demeter, co-author of the study, analyzes the molar.
Photo: F. Demeter et al., 2022

“We know this is the tooth of a girl who died when she was between 4 and 8 years old,” Shackelford said. “Since this tooth is from a child, we are currently performing additional analyzes of the growth and development of the teeth.”

Clement Zanolli, an expert on the evolution of human teeth and co-author of the new study, said the identification of Denisovan’s molar came from multiple lines of morphological evidence. The Laotian molar, he told me, resembles the teeth found on the partial mandible of Denisova from Tibet, including the large dimensions of the teeth and various distinctive features that set it apart from other Homo species known to inhabit Southeast Asia, including Neanderthals and modern humans.

“Among the human groups previously mentioned, the molar of Laos is closest to the Neanderthals, and we know from paleogenetics that the Denisovans were a sister group to Neanderthals, meaning they were closely related and shared morphological characteristics,” Zanolli, who works at the University of Bordeaux, explained in an email. . “For these reasons, the most parsimonious hypothesis is that the tooth we found in Laos belongs to a Denisovan.”

It is not impossible that the molar belonged to a Neanderthalbut if so, that “would make it the most southeastern Neanderthal fossil ever discovered,” according to the article.

“We are convinced that it is Denisovan”, Fabrice Demeter, a paleoanthropologist at the University of Copenhagen and co-author of the study, told me in an email. But to “further confirm our findings if necessary, genetic analyzes would be helpful,” he said. Unfortunately, “DNA tends to fragment faster and more intensely in tropical environments”, and it is for this reason that “no ancient DNA from any Pleistocene human has been sequenced so far. “, he added.

The new fossil is important because it confirms something already suggested by genetic data – that the Denisovans once inhabited a large area of ​​Southeast Asia. Additionally, it “confirms that Denisovans were present in this region and could have encountered Late Pleistocene modern humans,” according to Zanolli. And finally, it shows that The Denisovans could live in both high altitude cold environments and tropical forests of Southeast Asia.

The Denisovans seem to have been an adaptable group. But that makes their sudden disappearance around 50,000 years ago all the more mysterious.


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