Divers exploring the submerged cave systems of Mexico’s Yucatán Peninsula have recovered at least 11 prehistoric human skeletons over the past three decades, along with a large deposit of Ice Age animal bones. The discoveries have reshaped scientific understanding of when humans first reached the Americas, though several key questions remain unresolved.
The Yucatán Peninsula sits on a vast slab of porous limestone with almost no rivers on its surface. Rainfall filters directly through the rock, and over millions of years, slightly acidic water slowly dissolved the underground limestone, creating an extensive network of tunnels, chambers, and passages. As these hidden routes widened, some thin sections of limestone ceiling collapsed, forming circular sinkholes known locally as cenotes. Researchers estimate that roughly 6,000 cenotes are scattered across the Yucatán, many connected to the same underground cave system.
Divers have spent decades mapping these passages. Two systems in particular, Sac Actun and Ox Belha, have repeatedly traded the record for the world’s longest known underwater cave. Sac Actun expanded dramatically after divers connected it to a separate system in 2007 and later to another in 2018, reaching a surveyed length of more than 350 kilometers. Ox Belha has since surpassed that figure, with recent surveys recording over 500 kilometers of mapped passages, making it the longest single phreatic cave system documented on Earth.
Within these tunnels, divers encounter haloclines, distinct boundaries where lighter freshwater from above meets denser saltwater rising from the sea. The freshwater layer, fed entirely by rainwater seeping through the limestone above, provides the region’s only significant source of drinking water. Because of this, any construction project threatening the cave systems carries consequences that extend well beyond archaeology.
The first major discovery came in 2006, when German cave divers entered a cave near Tulum called Chan Hol, meaning “small hole” in the Maya language. After swimming roughly 1,800 feet through narrow, dark tunnels, they found a human skeleton later nicknamed “the Young Man of Chan Hol.” They reported the find to archaeologists at Mexico’s National Institute of Anthropology and History.
A research team led by Arturo González, director of the Desert Museum in Saltillo, studied and documented the bones in place for years before carefully bringing them to the surface. The skeleton was considered remarkably complete at about 60 percent, and researchers believed it had lain there for at least 10,000 years. The logic was straightforward: after the tunnels filled with water, no one could have carried a body that deep into the cave system.
Around the same time, researchers working in a nearby cave called Naharon recovered another skeleton nicknamed “the Woman of Naharon” or “Eve of Naharon.” Radiocarbon dating of collagen from her bones placed her at roughly 11,570 years old. Together, the two finds suggested the region had been inhabited by humans far earlier than many traditional timelines for the Americas had proposed.
A third skeleton, Chan Hol 3, was formally described in a 2020 journal paper. Researchers applied uranium and thorium dating to a flowstone that had formed just above her finger bones, estimating her minimum age at about 9,900 years. Her skull showed three distinct traumatic wounds and evidence of a possible bacterial infection related to treponemal disease, a category that includes yaws and syphilis. Whether the skull fractures resulted from an accident, violence, or something else has not been determined, and the research team was cautious about speculating.
Separately, researchers studying the same cave system found extensive charcoal layers throughout, later radiocarbon-dated to roughly 9,000 to 7,000 years old. These were interpreted as remains of small fires lit by early visitors to navigate the darkness. The evidence suggests people moved through Chan Hol for more than a thousand years before rising water eventually closed the cave for good.
In 2007, three divers exploring a section of the Sac Actun network found a large bell-shaped pit descending more than 200 feet into darkness. They named it Hoyo Negro, Spanish for “black hole.” At its bottom lay bones from at least 28 different animal species, a collection of creatures that had fallen into the pit over thousands of years before it flooded permanently. Among the fossils were remains of a short-faced bear, a species larger and more robust than any living bear; a saber-toothed cat; and gomphotheres, extinct elephant relatives with unusual jaw structures.
Researchers led by Blaine Schubert of East Tennessee State University published their findings in the journal Biology Letters, dating the bones from roughly 38,000 to 412,850 years old. The short-faced bear discovery was particularly significant because researchers previously had almost no fossil record of this particular type of bear outside South America. Hoyo Negro provided the most reliable documented evidence that these animals lived much farther north, deep in what is now Mexico.
Hoyo Negro also yielded the remains of a teenage girl nicknamed “Naia.” Radiocarbon dating placed her at roughly 12,900 to 11,750 years old. Divers and researchers have suggested she may have entered the cave system in search of freshwater while the pit was dry and died after falling in the dark. Rising water later preserved her remains and eventually sealed the entire system.
In 2010, Mexico’s National Institute of Anthropology and History created a dedicated Hoyo Negro underwater archaeology project, bringing together paleontologists, archaeologists, and divers from Mexico, Canada, and the United States. Over the years, the team’s mapping methods evolved significantly, moving from basic tools such as compasses, guide lines, and measuring tape to a technique called structure-from-motion photogrammetry, which stitches thousands of underwater photographs into an accurate three-dimensional digital model of the entire pit and its contents.
In November 2025, cave diver and archaeologist Octavio del Río, working with the National Institute of Anthropology and History, found another prehistoric human skeleton inside a submerged cave system near Tulum. Reaching the remains required swimming roughly 650 feet through flooded tunnels, with the skeleton found about 26 feet below the surface, resting on a mound of sediment beside an interior chamber.
Del Río noted that the skeleton’s specific location was significant. Given its position and depth, the remains could only have arrived while the cave was dry, since no person without modern diving equipment could have carried a body that deep into a flooded tunnel system. This reasoning, based on distance and depth, rules out the possibility of burial after the flooding.
What made this particular skeleton distinctive was the apparent deliberate placement of the bones. Del Río and his colleagues noted that the arrangement did not appear accidental but suggested an intentional burial, possibly connected to rituals performed by people living in the region before the cave flooded. If further research supports this interpretation, it would indicate that humans were deliberately using the cave as a burial site long before the Maya built their first temples in the area.
According to del Río, this was the eleventh prehistoric human skeleton recovered from the Yucatán’s submerged caves in the past three decades, adding to an already rich regional record. Genetic evidence from several of these skeletons, including Naia, has generally supported connections to northeast Asian populations who crossed the Bering land bridge, though other evidence has pointed toward the possibility of separate migration routes.
The ongoing research has become entangled with a modern controversy. Since 2022, the Mexican government has been building the Tren Maya, an ambitious tourism rail project intended to connect resort cities and archaeological sites across the Yucatán Peninsula. A section of track stretching more than 60 meters through jungle between Cancún and Tulum passes directly over some of the fragile cave systems from which these ancient skeletons have been recovered, including areas near both Sac Actun and Ox Belha.
Del Río, who has spent years diving and documenting this particular section of the cave, has publicly expressed concern that construction could cause cave systems to collapse, become contaminated, or be permanently closed before archaeologists have a proper chance to study them. In September 2022, he and fellow diver Peter Broward discovered another prehistoric skeleton in a cave near jungle already cleared for the train, with a skull that was broken and partly covered in sediment. Del Río decided not to publicly reveal the exact location of that cave, fearing the site could be looted or damaged.
The National Institute of Anthropology and History acknowledged the discovery and confirmed that its Quintana Roo state branch would investigate the site through its Holocene archaeology project. Del Río has argued that the train route should have followed the already developed coastal highway between Cancún and Tulum rather than cutting new path through untouched jungle above the cave system.
Concerns continued after the initial construction phase. In early 2026, publicly circulated footage showed visible subsidence, vibration, and cracks in structural support columns along a section of the railway, prompting Mexico’s federal government to order a formal technical assessment of the foundations in coordination with military engineers. These structural concerns, in an area known for limestone caves that can collapse without warning when the rock beneath them becomes unstable, highlight exactly the kind of risk researchers had warned about years before construction finished.
In response to growing concerns over both the fragile cave ecosystem and its archaeological importance, Mexican authorities have moved toward formally declaring the underground river network a protected natural and cultural heritage area, with a target of completing the designation by 2026. Whether that protection arrives in time to safeguard what remains unexplored beneath the jungle is a question no one has yet been able to answer.
Despite eleven skeletons, a pit full of Ice Age megafauna, and years of dedicated fieldwork, genuine disagreements remain over several key questions raised by the region. Dating is one of the main areas of dispute, because the degradation of collagen in underwater bones makes standard radiocarbon testing unreliable, forcing researchers to rely on alternative methods such as uranium and thorium dating of surrounding minerals, which provide only a minimum age rather than a precise one.
Migration routes are equally contested. Skull-shape evidence from Chan Hol and Naharon has led some researchers to argue for multiple distinct waves of early migration to the Americas from different source populations at different times. Other scientists caution against drawing firm conclusions from skull shape alone, noting that skull form can change across generations due to diet and environment rather than ancestry alone.
The question of what purpose these burials served also remains unresolved. Del Río’s team believes the newest 2025 skeleton points to an intentional ritual burial, but confirming that interpretation, rather than an accidental fall or a simple resting place, requires more careful study of exactly how and where the bones were placed. Similar caution applies to the fractures on the Chan Hol 3 skull, where researchers have refrained from definitively declaring whether the injuries resulted from violence, accident, or illness.
Even the basic measurements of these cave systems continue to shift. The title of world’s longest underwater cave has changed hands several times between Sac Actun and Ox Belha over the past two decades as new connecting passages were discovered and surveyed. This means the total extent of unexplored tunnels, and what they might still contain, remains unknown even to researchers who have spent their entire careers mapping the region.
These ongoing disagreements are not a weakness in the research. They reflect the careful, repeated verification required before any significant archaeological claim is accepted by the broader scientific community. For this reason, researchers continue returning to the same submerged tunnels, treating each new skeleton not as a final verdict but as another piece of an incomplete picture.
The situation is straightforward. Underwater explorers in Mexico’s Yucatán cave systems have recovered at least eleven prehistoric human skeletons and an entire deposit of extinct Ice Age animals from a single pit called Hoyo Negro. These caves, carved gradually by rainwater cutting through limestone over millions of years, remained dry throughout the last Ice Age. Rising sea levels flooded them roughly 8,000 years ago, trapping remains that would otherwise have decomposed completely on the open surface.
The skeleton of the Young Man of Chan Hol, discovered by German divers in 2006, sparked genuine scientific debate when researchers dated the surrounding minerals to at least 11,300 years old, with chemical evidence suggesting the true age could be closer to 13,000 years. Two additional skeletons from the same cave, along with the Woman of Naharon and the Naia skeleton from Hoyo Negro, added further data while also creating more disagreement over migration routes, skull shape, and dating methods.
In November 2025, an eleventh skeleton was discovered in a cave near Tulum, which researchers believe was part of a planned religious burial. It was recovered at a time when a controversial modern train project running directly above several of these cave systems was facing its own investigation over structural safety.
The full picture does not form a neat, settled story. Decades of careful repeated dives, conflicting dating methods, and open scientific disagreement have produced the incomplete portrait available today. With hundreds of miles of unexplored tunnels remaining beneath the jungle, no one can yet say with complete confidence exactly who these people were or precisely how they first arrived.
