Scientists discover oldest intact skeleton in New World

An accidental underwater discovery made by a group of recreational scuba divers in a remote cave in Mexico’s Yucatán Peninsula has yielded the oldest intact human skeleton ever found in the Americas, a find which holds important clues in the debate about the origins of the first Americans, according to a new research paper published Thursday in the journal Science.

Divers discovered the nearly complete skeleton of a teenage girl from the Late Pleistocene age in an underwater cave, Hoyo Negro, just outside Tulum. An international team of scientists and divers has determined that Naia, as she has been nicknamed, is 12,000 to 13,000 years old.

What’s more, Naia’s skull and facial characteristics are different from those of modern Native Americans and has characteristics more in common with people from Africa and Australia. But after a rigorous genetic analysis of the enamel on her teeth and the minerals found in her bones, the scientists discovered that although she was found in Mexico, Naia shares certain genetic characteristics with the earliest hunter-gatherers thought to have crossed the Bering land bridge from northeastern Asia into the Americas 18,000 to 26,000 years ago.

“Thus Naia, one of the earliest occupants of the Americas yet encountered, suggests that the paleo-Americans [the earliest Americans] do not represent an early migration from a part of the world different than that of Native Americans,” archaeologist James Chatters, the lead author of the study, said in a release. “Rather, paleo-Americans and Native Americans descended from the same Beringian source.”

Because modern Native Americans have different genetic characteristics from those Beringian ancestors, some scientists think multiple groups migrated from Eurasia to the Americas, Chatters told Al Jazeera. But others insisted it was one group that spread southward and that the differences between them and modern Native Americans evolved later.

Naia marks the first time that scientists have been able to match an early American skeleton with DNA linked to the Beringian hunter-gatherers, supporting the single-migration theory and suggesting they may have spread much farther across the Americas than previously thought.

“It’s good, strong evidence,” Chatters said, but with the caveat that it’s just one skeleton. “It’s still a powerful step in that direction.”  

That Naia was found submerged in a cave filled with chemically neutral water that was sealed off from oxygen for at least 8,000 years helped conserve the bones, Chatters said.

The scientists say that people and animals likely fell into this cave and became trapped and that about 10,000 years ago the climate began to warm and glaciers melted, filling the cave with water.

Chatters said finding a nearly complete skeleton more than 12,000 years old is extremely rare. Other specimens he has examined through the years, such as the Kennewick man, discovered in the state of Washington in 1996, were not more than 10,000 years old, and they’re often just fragments, making it difficult to analyze their DNA.

“Part of it was a political reason,” he said, referring an eight-year legal battle he fought with Native American tribes in Washington, who as part of their burial rituals wanted to rebury the Kennewick man. “Part of it’s the practicality that we didn’t have the methods to extract the DNA effectively from poorly preserved material,” he said, “and part of it is the extreme rarity of the skeletons.”

“But now,” he said, “we are getting the ability to get nuclear genetic material in small quantities. We’ve got the computers doing the job for us. And all of a sudden, the field is just moving at 100 miles per hour.”

So far, they’ve used photography, videography, 3-D modeling and minimal sampling to study the cave, starting with the human skeleton.

Determining Naia’s age, Chatter said, was a group effort. Three research institutions did radiocarbon dating of the enamel from her teeth, and he and other scientists decided that uranium-thorium dating could be used to analyze the mineral deposits in her bones. In addition to that, they analyzed the water levels and considered the types of animals also found in the cave and were able to determine that she was 12,000 to 13,000 years old.

In order to extract Naia’s DNA, the team needed to use divers.

Alberto Nava, a software engineer from Monterey, California, discovered the cave back in 2007 on a dive with two friends, Alex Alvarez and Franco Attolini. He has been scuba diving for 20 years and is a longtime cave explorer with the California-based Bay Area Underwater Explorers, a nonprofit underwater exploration and conservation group.

But the men never expected to make such a once-in-a-lifetime discovery when diving in a pool they found in the jungles near Tulum, which is known for its water-filled sinkholes, called cenotes.

They found the cave after making their way down a mile-long tunnel and were suddenly in a pitch-black expanse that wasn’t accessible from the surface. Since they couldn’t see anything around them, they called it Hoyo Negro, which in Spanish means “black hole.”

They returned a few months later with special lighting equipment and were amazed to see a dome-shaped cave about 200 feet in diameter. “The moment we entered the site,” Nava said, “we knew it was an incredible place.”

First, Nava said, the men spotted a giant, three-foot-long femur resting against the wall. Next they saw a five-foot-wide pelvis. And Alvarez spotted a human skull sitting on a top of a ledge, with all its teeth intact — part of the young girl they later dubbed Naia.

As their eyes adjusted, they saw a cave full of what they later discovered was full of the intact skeletons of 26 different mammals, including pumas, bears and extinct animals such as a saber-toothed tiger and several ground sloths.

In his 20 years of scuba experience, Nava had seen a few bones of birds and small rodents but nothing like this. “For us, this is the discovery of our lifetimes,” he told Al Jazeera.

He added, “We were not going in there to find the oldest American. We were three friends planning to explore some caves in Mexico, and all of a sudden we ran into this. But we did take it seriously.”

The men returned multiple times to take photographs and eventually shared their findings with the Mexican government’s National Institute of Anthropology and History. The team of archaeologists and paleontologists there wanted to make sure they didn’t disturb or damage the artifacts, so they extracted the tiniest possible DNA samples from the skeleton’s teeth.

And in a unique twist, the scientists spent more than a year training Nava, Alvarez and Attolini in archaeology and paleontology to keep them involved in the project and incorporated the men into the diving team that has been exploring and documenting the contents of the cave, with support from the National Geographic Society.

“We ended up being the hands and eyes of the researchers,” Nava said.

Normally, the discoverers of such bones would not be so involved in the research process, but “we wanted to respect these people and their capabilities and basically their primacy in the story,” Chatters said.