EVANSTON, Ill. --- Cave-diving scientist Patricia A. Beddows of Northwestern University is a member of an international team this week announcing that a near-complete skeleton of a teenage girl -- discovered in 2007 in an underwater cave on Mexico’s Yucatán Peninsula -- is one of the oldest human skeletons found in North America.
Scientists have determined the prehistoric girl is between 13,000 and 12,000 years old, and also her remains establish a definitive genetic link between the earliest Americans and modern Native Americans.
Details of “Naia,” who went underground in an extensive cave system to seek water and fell to her death in a large pit named Hoyo Negro (“black hole” in Spanish), will be published May 16 in the journal Science.
Beddows, one of the research team’s two cave-diving scientists who have been underwater at Hoyo Negro, has hovered above the skeleton’s site and prospected in the area.
“The preservation of all the bones in this deep, water-filled cave is amazing -- the bones are beautifully exposed on the rock of the cave floor,” said Beddows, a co-author of the paper. “The girl’s skeleton is exceptionally complete because of the environment in which she died -- she ended up in the right water and in a quiet place without any soil. Her pristine preservation enabled our team to extract enough DNA to determine her shared genetic code with modern Native Americans.”
Beddows is assistant chair and assistant professor of instruction in the department of Earth and planetary sciences in Northwestern’s Weinberg College of Arts and Sciences.
Extensive genetic analysis shows the prehistoric girl and living Native Americans came from the same place -- Beringia, what is now northwest Alaska and the Russian Far East -- during the initial peopling of the Americas.
Led by Pilar Luna of the Mexican government’s National Institute of Anthropology and History (INAH) and James C. Chatters of Applied Paleoscience, 15 experts from a wide range of fields have been focused on telling the story of the young woman and Hoyo Negro since the skeleton’s surprising discovery by exploration cave divers Alejandro Alvarez, Alberto (Beto) Nava Blank and Franco Attolini. The dive team named her “Naia,” from a Greek word meaning “water nymph.”
Beddows’ research focuses on cave systems that are carved by dissolution of soluble carbonate rocks such as limestone and dolomite, and her biggest research concentration is the flooded caves of the Yucatán Peninsula, including Hoyo Negro.
To the complicated conservation project and scientific investigation, she contributed her expertise on the complex formation of the caves, the flow of groundwater in the cave system as well as changing sea levels, and sediments at the site and on the skeleton.
“I and some of the other divers had noticed that crystals were growing on the bones of the girl’s skeleton,” Beddows said. “These calcite crystals are recrystallized rock minerals from water. Analysis of this material allowed us to date the skeleton to a time that converged with other independent chronology work. Her body was laid down first and then the crystals, which are just a bit younger than the bones, formed.”
The near-complete human skeleton -- with an intact cranium and preserved DNA -- was discovered lying 130 feet below sea level near a variety of extinct animals, including an elephant-like creature called a gomphothere and a saber-toothed cat. The location of the bones and the crystals helped the scientists understand how the water level in Hoyo Negro changed over time, which is tied to rising and falling global sea levels, Beddows said.
“These discoveries are extremely significant,” said 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 Yucatán 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.
According to Chatters, the paper’s lead author, “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.”
Beddows’ contributions to the Hoyo Negro research are primarily in three areas:
- Cave formation. “Hoyo Negro is a very complex site,” Beddows said. “By understanding the formation of the shallow caves and the shaft into which the girl fell, we know that the girl and the animals visited a site that looks almost like it does today, except that the water level was down in the bottom of the shaft.”
- Hydrogeology. Beddows’ studies starting in the mid-1990s have shown how these extensive caves effectively drain groundwater to the coasts and, more specifically, how the water level in the caves matches sea level very closely. “Using this knowledge, we understand how Hoyo Negro has changed over thousands of years,” Beddows said.
- Recrystalized rock sediments. The rocks and the skeletons in Hoyo Negro have valuable rock crystals lying on them, including a new form of impressive crystal that Beddows calls “florets,” in recognition of their bushy nature and one-inch size. “An impressive aspect of this research is that we have dated the skeleton directly, but we also have supported these dates with additional dates on the florets,” Beddows said.
She says research in flooded caves is much like space exploration -- it’s very exciting, there is no “easy out” and communication is limited.
“Similar to astronauts, divers are reporting back to ‘mission control’ -- to a much larger scientific team at the surface,” Beddows said. “It all has to be done on SCUBA, which is our life support system. Our science team has been supported by a great number of dedicated non-science cave divers who have committed hundreds of hours at very dangerous depths to complete this exploration.”
The title of the Science paper is “Late Pleistocene Human Skeleton and mtDNA Link Paleoamericans and Modern Native Americans.”
In addition to Beddows, Luna and Chatters, other authors of the paper are from the Archaeological Institute of America, the Waitt Institute, The University of New Mexico, The Pennsylvania State University, The University of Texas at Austin, University of Illinois at Urbana-Champaign, DirectAMS, McMaster University and Washington State University.
The National Geographic Society supported the research. Its press release is available online.
The Hoyo Negro expedition will be featured in National Geographic magazine and on a National Geographic Television program airing on the PBS series “NOVA” in 2015.