Archaeologists discover new bone fragments which were 86,000 years ago in a cave in northern Laos

Archaeologists have discovered two new bone fragments in a cave in northern Laos, suggesting that Homo sapiens roamed Southeast Asia as recently as 86,000 years ago. The findings, published this week in Nature Communications1, suggest that humans migrated through the area earlier than previously thought.

Over a decade, excavations at Tam Pà Ling Cave uncovered seven bone fragments sandwiched between layers of clay. Laura Shackelford, an anthropologist at the University of Illinois Urbana–Champaign, and her colleagues regularly had to walk through sticky tropical heat to reach the mountaintop cave.

After digging 7 meters down, the excavations finally hit bedrock and the team was able to reconstruct the complete chronology of the cave, Shackelford says. Sediment and bones discovered in the cave show that modern humans have inhabited the mountain area for at least 68,000 years and passed through even earlier.

“I can’t overstate the importance of another point on our map for early modern humans in Southeast Asia,” says Miriam Stark, an anthropological archaeologist at the University of Hawaii at Manoa, who was not involved in the work. “Understanding Southeast Asia is essential to understanding the deep history of the world,” he says.

Old bones

The newly discovered bones are a small piece of skull and a fragment of a tibia. The remains were probably swept into an uninhabited cave during a flood. Scientists dated herbivore teeth found alongside human fossils using electron spin resonance and uranium series dating.

They also estimated the age of the cave sediment using luminescence dating, which counts when photons last illuminated the ground. Together, the results date the skull fragment and tibia to approximately 70,000 and 77,000 years, respectively. But the tibia could be as old as 86,000 years.

This is much older than the first fossil discovered at the site more than a decade ago, a piece of skull estimated to be 46,000 years old2. It is also older than other cave bones – two jaw fragments, a rib and a foot bone – which are between 46,000 and 70,000 years old3-5.

The fossil record in Southeast Asia is limited, in part because the tropical climate decomposes most bones. The details of when the first humans first arrived in the region, where they came from and where they migrated are still up for debate, Shackelford says.

Laos lies on a potential migration route to Australia, where the oldest archaeological site is about 65,000 years old6. In addition to contributing data to an understudied area, Tam Pà Ling provides additional insights into the timing of migration in the region.

Some human migration hypotheses use DNA analysis to argue that H. sapiens dispersed in a single rapid event after a geological period, called Marine Isotope Stage 5, which lasted between 130,000 and 80,000 years ago. However, the Tam Pà Ling fossils do not match these models. Instead, the fossils indicate that dispersal occurred before the end of marine isotopic phase 5.

“We see something different,” Stark says. That doesn’t mean the genetic models are wrong, he says, just that the picture they reveal is incomplete.

The shape of the Tam Pà Ling fossils further complicates the story. Although they come from H. sapiens, the youngest bone — a 46,000-year-old skull fragment — has a mixture of characteristics of both archaic and modern humans, while the oldest fossils have more modern features. For example, the older skull fragment lacks the prominent eyebrows associated with more archaic humans, which are seen to some extent in the younger fossil.

This is counterintuitive, Shackelford says, and suggests that the older fossils may not have evolved from local populations, but rather represent groups of early modern humans that migrated through the area. Armand Mijares, an archaeologist at the University of the Philippines Diliman in Quezon City, says this is a plausible interpretation, but more evidence is needed to be sure.

Shackelford and her colleagues will continue to excavate the cave to look for more fossils. They are also trying to extract environmental DNA from the soil, which could provide clues about what flora and fauna lived in the area tens of thousands of years ago. Discoveries beyond the cave could also yield valuable insights into the region’s early human inhabitants.

Written by: Vaishali verma

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Reference : https://www.nature.com/articles/d41586-023-01903-3