A skeleton clue to early American ancestry

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The skeletal remains of a teenage female from the late Pleistocene or last ice age found in an underwater cave in Mexico have major implications for our understanding of the origins of the Western Hemisphere’s first people and their relationship to contemporary Native Americans.

A skeleton clue to early American ancestry
In this June 2013 photo provided by National Geographic, diver Susan Bird, working at the
 bottom of Hoyo Negro, a large dome-shaped underwater cave in Mexico’s Yucatan
 Peninsula, brushes a human skull found at the site while her team members take 
detailed photographs [Credit: National Geographic, Paul Nicklen]

In a paper released today in the journal Science, an international team of researchers and cave divers present the results of an expedition that discovered a near-complete early American human skeleton with an intact cranium and preserved DNA. The remains were found surrounded by a variety of extinct animals more than 40 meters (130 feet) below sea level in Hoyo Negro, a deep pit within the Sac Actun cave system on Mexico’s Yucatan Peninsula.

“These discoveries are extremely significant,” said Pilar Luna, INAH’s director of underwater archaeology. “Not only do they shed light on the origins of modern Americans, they clearly demonstrate the paleontological potential of the Yucatan Peninsula and the importance of conserving Mexico’s unique heritage.”

The findings detailed in Science are noteworthy on numerous levels:

  • This is the first time researchers have been able to match a skeleton with an early American (or Paleoamerican) skull and facial characteristics with DNA linked to the hunter-gatherers who moved onto the Bering Land Bridge from northeast Asia (Beringia) between 26,000 and 18,000 years ago, spreading southward into North America sometime after 17,000 years ago.
  • Based on a combination of direct radiocarbon dating and indirect dating by the uranium-thorium method, it is one of the oldest skeletons discovered in the New World.
  • It is clearly the most complete skeleton older than 12,000 years as it includes all of the major bones of the body and an intact cranium and set of teeth.

A skeleton clue to early American ancestry
Cave diver Alexandro Alvarez inspects the newly-discovered skull of Naia,
 the 12,000-13,000 year-old human skeleton discovered in a submerged 
cave on the Yucatan peninsula of Mexico. An international team of researchers 
detailed their analysis of what is the oldest most complete, genetically intact 
human skeleton in the New World in a paper published today in the journal Science 
[Credit: Photo by Daniel Riordan Araujo]

According to the paper’s lead author, James Chatters of Applied Paleoscience, “This expedition produced some of the most compelling evidence to date of a link between Paleoamericans, the first people to inhabit the Americas after the most recent ice age, and modern Native Americans. What this suggests is that the differences between the two are the result of in situ evolution rather than separate migrations from distinct Old World homelands.”

The field research team endured extremely challenging conditions to access the skeleton’s remote underwater location at the bottom of Hoyo Negro, deep beneath the jungles of the eastern Yucatan Peninsula. The multidisciplinary team, composed of professional divers, archaeologists and paleontologists, extensively documented the bones in situ.

Alberto Nava with Bay Area Underwater Explorers was part of the team that first discovered Hoyo Negro in 2007. “We had no idea what we might find when we initially entered the cave, which is the allure of cave diving,” said Nava. “Needless to say, I am incredibly proud to be part of the efforts to share Hoyo Negro’s story with the world.”

Assessing the skeleton’s age required a novel approach given the challenging environmental conditions. The research team analyzed tooth enamel and bat-dropped seeds using radiocarbon dating and calcite deposits found on the bones using the uranium-thorium method, establishing an age of between 12,000 and 13,000 years. They used similar methodology to date the remains of a variety of gomphothere (an extinct relative of the mastodon) found near the skeleton to around 40,000 years ago. The more than 26 large mammals found at the site included saber-toothed cats and giant ground sloths, which were largely extinct in North America 13,000 years ago. The skeleton’s age was further supported by evidence of rising sea levels, which were as much as 360 feet (120 meters) lower during the last ice age than they are today.

A skeleton clue to early American ancestry
New genetic evidence supports the hypothesis that the first people in the Americas all came
 from northeast Asia by crossing a land bridge known as Beringia. When sea levels rose 
after the last ice age the land bridge disappeared [Credit: Julie McMahon]

The extremely small skeleton is of a very delicately built woman measuring only 4’10” tall. Named “Naia” by the dive team, she is estimated to have been between 15 and 16 years old at the time of her death, based on the development of her skeleton and teeth.

Analyses of DNA extracted from the skeleton’s wisdom tooth found it belonged to an Asian-derived lineage that occurs only in America (haplogroup D, subhaplogroup D1). Finding a skeleton with DNA from one of America’s founding lineages in Central America greatly expands the geographic distribution of confirmed Beringians among the earliest Americans.

The Hoyo Negro project was led by the Mexican government’s National Institute of Anthropology and History (INAH) and supported by the National Geographic Society.

Source: National Geographic Society [May 15, 2014]

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