Denisovan Tooth from Laos’s Cobra Cave?

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Denisovan Tooth from Laos’s Cobra Cave? May 17, 2022 19:02:27 GMT

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Post by Admin on May 17, 2022 19:02:27 GMT

(CNN)A tooth unearthed from a remote cave in Laos is helping to sketch an unknown chapter in the human story.

Researchers believe the tooth belonged to a young female who lived at least 130,000 years ago and was likely a Denisovan -- an enigmatic group of early humans first identified in 2010.

The lower molar is the first fossil evidence placing Denisovans in Southeast Asia and may help untangle a puzzle that had long vexed experts in human evolution.

The only definitive Denisovan fossils have been found in North Asia -- in the eponymous Denisova cave in Siberia's Altai Mountains in Russia. Genetic evidence, however, has tied the archaic humans most closely to places much further south -- in what's now the Philippines, Papua New Guinea and Australia.

"This demonstrates that the Denisovans were likely present also in southern Asia. And it supports the results of geneticists who say that modern humans and the Denisovans might have met in Southeast Asia," said study author Clément Zanolli, a researcher in paleoanthropology at CNRS, the French National Center for Scientific Research and the University of Bordeaux.

Archaeologists uncovered the tooth in a place known as Cobra Cave, 160 miles (260 kilometers) north of Laos' capital, Vientiane, where excavations began in 2018. The study, which published in the journal Nature Communications on Tuesday, estimated the molar was between 131,000 and 164,000 years old, based on analysis of cave sediment, the dating of three animal bones found in the same layer, and the age of rock overlying the fossil.

The tooth was unearthered from a cave in Laos and belonged to a woman who lived at least 131,000 year ago.

"Teeth are like the black box of an individual. They preserve a lot of information on their life and biology. They have been always used by paleoanthropologists, you know, to describe species or to distinguish between species. So for us paleoanthropologists (teeth) are very useful fossils," Zanolli said.

Comparison with archaic human teeth
The researchers compared the ridges and dips on the tooth with other fossilized teeth belonging to archaic humans and found it didn't resemble teeth belonging to Homo sapiens or Homo erectus -- an archaic human that was the first to walk with an upright gait whose remains have been found across Asia. The cave find most closely resembled a tooth found in a Denisovan jawbone found on the Tibetan plateau in Xiahe county, in Gansu province, China. The authors said it was possible, though less likely, it could belong to a Neanderthal.

Analysis of some protein in enamel from the tooth suggested that it belonged to a female.
Denisovan DNA lives on in some humans today because, once our Homo sapiens ancestors encountered the Denisovans, they had sex with them and gave birth to babies -- something geneticists call admixture. This means we can look back into human history by analyzing current-day genetic data.

The "admixing" happened was thought to have happened more than 50,000 years ago, as modern humans moved out of Africa and likely crossed paths with both Neanderthals and Denisovans. But pinning down exactly where it happened has proven difficult -- particularly in the case of Denisovans.

Definitively Denisovan?
Any addition to the meager hominin fossil record of Asia is exciting news, said Katerina Douka, an assistant professor of archaeological science at the department of evolutionary anthropology at the University of Vienna. She wasn't involved in the research.

She said she would have liked to see "more and extensive evidence" that the tooth was definitively Denisovan.

"There is a chain of assumptions the authors accept in order to confirm that this is a Denisovan fossil," she said.
"The reality is that we cannot know whether this single and badly preserved molar belonged indeed to a Denisovan, a hybrid or even an unknown hominin group. It might well be a Denisovan, and I would love it to be a Denisovan, because how cool would that be? But more confident evidence is needed," she said.

In deeming the Laos tooth Denisovan, the researchers in this study relied heavily on a comparison with the Xiahe jawbone, Douka said. However, the jawbone, while thought by many to be Denisovan, was not an open-and-shut case. No DNA had been retrieved from the fossilized jawbone, only "thin" protein evidence, she added.

"Anyone working on this hominin group, where many major questions still remain, wants to add new dots on the map. The difficulty is in reliably identifying any fossils as that of a Denisovan," she said. "This lack of robust biomolecular data, however, reduces significantly the impact of this new find and it is a reminder of how difficult it is to work in the tropics."

The study authors said they planned to try and extract ancient DNA from the tooth, which, if possible, would provide a more definitive answer but the warm climate means that could be a long shot. The research team also plans to continue excavating the site after a pandemic-induced hiatus in the hope of more discoveries of ancient humans that lived in area.

"In this kind of environment, DNA doesn't preserve well at all but we'll do our best," said study coauthor Fabrice Demeter, an assistant professor at the Lundbeck Foundation GeoGenetics Centre in Denmark.

Last Edit: May 19, 2022 19:07:29 GMT by Admin

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Denisovan Tooth from Laos’s Cobra Cave? May 17, 2022 19:57:34 GMT

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Post by Admin on May 17, 2022 19:57:34 GMT

After scrambling up a steep rocky pitch in the Annamite Mountains of Laos, Laura Shackelford was initially underwhelmed. The paleoanthropologist from the University of Illinois Urbana-Champaign stood in a cramped hollow known as Cobra Cave, looking for bones that a local Hmong boy had mentioned seeing. Flipping on her flashlight, she swept the beam of light from one seemingly barren wall to another.

Then she looked up.

“I saw almost nothing but bone,” says Shackelford, who is also a National Geographic Explorer. Embedded in the rubbly ceiling were fossils of animals long gone, scattered across the cave’s roof “almost like stars.”

For years Shackelford and her team had worked in Laos’s labyrinthine cave systems in search of ancient human remains, and she knew that this narrow passage was special. Shortly before her first trip into the cave, Shackelford’s colleague had found a particularly exciting fossil within the cave’s constellations of remains: a wrinkly partial molar more than 130,000 years old.

As Shackelford and her colleagues report in a new study partially funded by the National Geographic Society, the tooth is likely from a young girl who was part of a mysterious group of ancient humans known as the Denisovans. If confirmed, the find marks the southernmost fossil found to date of this enigmatic group.

Denisovans split from their sister group, the Neanderthals, some 400,000 years ago as Neanderthals spread across Europe and Denisovans moved east into Asia. While scientists have uncovered many Neanderthals remains, Denisovan fossils have proven elusive. All of the previously confirmed Denisovan bones and teeth could easily fit in a sandwich-size plastic bag, and they all come from just two sites, one in Siberia and another in Tibet.

But scientists have long suspected Denisovans traipsed much farther south. Whenever the Denisovans crossed paths with early humans, they seem to have interbred, leaving their genetic fingerprints in most modern people of Asian descent.

The latest find in Laos, published this week in Nature Communications, reveals the stunningly varied range that Denisovans achieved, from frigid mountains and high plateaus to the steamy lowlands of Southeast Asia. “It kind of makes me think about how similar they are to us,” Shackelford says. “We’re incredibly flexible—that’s sort of the hallmark of modern humans.”

The likely Denisovan tooth is one of many new finds that hint at how much more is just waiting to be discovered in the region. “I do have to say, we’re so proud,” says study co-author Souliphane Boualaphane, an archaeologist with Laos’s Ministry of Information, Culture, and Tourism.

Last Edit: May 17, 2022 20:41:52 GMT by Admin

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Denisovan Tooth from Laos’s Cobra Cave? May 17, 2022 20:38:39 GMT

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Post by Admin on May 17, 2022 20:38:39 GMT

Unearthing an ancient menagerie
The tooth is the latest fossil find from the Annamite Mountains, which sprawl about 700 miles along the border between Laos and Vietnam. Over millennia, rivers have carved out the local limestone—the remnants of an ancient seafloor—into a system of caves that now snake through the range.

Though these craggy confines have proven fertile grounds for discovery, they’re not easy places to work. The area’s hot, humid climate causes bone to break down rapidly, and the rugged terrain means that whatever survives is hard to find. Despite these challenges, recent discoveries in Laos have documented tens of thousands of years of human activity in the region, including some of Southeast Asia’s oldest modern human remains.

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Denisovan Tooth from Laos’s Cobra Cave? May 17, 2022 21:32:20 GMT

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Post by Admin on May 17, 2022 21:32:20 GMT

Jason Treat and Christine Fellenz, NGM Staff. Sources: Lee Berger, University of the Witwatersrand (Wits); John Hawks, University of Wisconsin-Madison; Fabrice Demeter

and others, Nature Communications, 2022.

Much of the modern research interest in Laos traces back to Thongsa Sayavongkhamdy, an influential Laotian archaeologist who painstakingly relocated sites that had been studied and abandoned in the 1930s, including the area that contains Cobra Cave. Sayavongkhamdy, a co-author on the new study, died in April; the study is dedicated to his memory. “It’s really thanks to him that our team has been able to work in Laos,” says Fabrice Demeter, the study’s co-lead author and a paleoanthropologist at the Lundbeck Foundation GeoGenetics Centre in Copenhagen, Denmark.

Demeter and Shackelford have each spent more than a decade working in Laos, recently teaming up with cavers to navigate the steep escarpments. In 2018 they caught wind of Cobra Cave, whose entrance sits atop a rock face more than 110 feet above the surrounding plain. The cave is so cramped, a person of average height standing inside can touch both walls and the ceiling all at once.

Retrieving the cave’s fossils is also tricky since they’re embedded within breccia, a fruitcake-like type of rock that forms from jumbles of stony fragments. Chipping through it “is like trying to excavate out of concrete,” Shackelford says.

Yet Cobra Cave yielded amazing finds from the start. On December 3, 2018, geologist and caver Eric Suzzoni headed to the hollow on a reconnaissance trip ahead of Shackelford’s first visit inside, and he collected bits of rock and bone to show the team. He clambered down from the cave just before lunch to pass around his many fossil finds. “At some point Eric said, Oh, but I got something here,” Demeter says. From his front shirt pocket, Suzzoni pulled out the unusual molar.

“Almost immediately, we knew that it was hominin of some sort,” Shackelford says. “But it wasn't modern human.”

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Denisovan Tooth from Laos’s Cobra Cave? May 18, 2022 17:41:02 GMT

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Post by Admin on May 18, 2022 17:41:02 GMT

A black box of life
For nearly a decade, the only known remains of Denisovans were a few teeth, a pinky bone, and a fragment of skull uncovered at Denisova cave in southern Siberia. Then in 2019 a blockbuster announcement revealed a Denisovan jaw—known as the Xiahe mandible—in Baishiya Cave, on the edge of the Tibetan Plateau.

The newfound Laotian molar may just be one tooth, but it could still add a lot to scientists’ understanding of Denisovans. “Teeth are like a little black box of the life of the individual,” says Clément Zanolli, the study’s co-lead author and a paleoanthropologist at France’s University of Bordeaux. In their shape, internal structure, chemistry, and wear patterns, teeth can preserve hints of an animal’s age, diet, and even the climate of their habitat.

Tooth shapes can also help scientists identify species among humans and their extinct cousins. The chewing surface of the Cobra Cave molar is much more wrinkled than that of modern human molars, and it has a crest that’s common within the teeth of Neanderthals. But the tooth’s overall shape and inner structure resemble the Denisovan teeth in the Xiahe mandible.

The Laotian tooth’s lack of roots or surface wear suggests that it belonged to a child who died before their adult teeth had fully formed, likely between 3.5 and 8.5 years of age. The molar probably washed into the cave alongside remains from other large animals, including ancient rhinos, pigs, macaques, and bovids. Based in part on the age of these animal remains, the molar is most likely between 131,000 and 164,000 years old.

After x-ray scanning the fossil to study its shape, the researchers sampled the tooth’s enamel in search of preserved proteins. Unlike delicate strands of DNA, proteins have a higher chance of surviving Laos’s hot, humid climate. The amino acid building blocks of these proteins can then give hints to the underlying genetic code, helping scientists untangle a specimen's identity.

This analysis revealed that the tooth belonged to an individual within the genus Homo, rather than an orangutan or other great ape. Proteins also show that the tooth belonged to a girl. Yet researchers didn’t find the proteins needed to place the tooth within a specific branch of the hominin family tree.

While the analysis cannot confirm Denisovan identity, “there’s nothing stopping us from looking for other proteins present in the enamel,” says study co-author Frido Welker, a paleogeneticist at the University of Copenhagen’s Globe Institute. As methods for extracting and analyzing DNA and associated proteins improve, Welker and his colleagues hope the tooth will yield more details.

And by minimizing the amount of sample they took from the tooth, the study team has left the door open for future research that’s yet to be imagined. “People who are working on this field in 30, 40, 50 years with totally new technologies are going to appreciate that," says National Geographic Explorer Kendra Sirak, a Harvard Medical School research associate and ancient DNA expert who wasn’t involved with the new study.