In 2007, cave divers mapping underwater tunnels near Tulum, Mexico, found a large submerged chamber they named Hoyo Negro. The room, about 100 feet deep, contained scattered animal bones and a nearly complete human skeleton. The discovery led to years of research by the Mexican National Institute of Anthropology and History (INAH) and a team of international scientists.

The human remains belonged to a young woman, aged 15 to 17, who researchers named Naia. Analysis suggested she entered the cave system seeking fresh water, a scarce resource when sea levels were much lower. Her skeleton showed evidence of a broken pelvis, likely from a fall. Researchers estimated her remains to be between 12,000 and 13,000 years old, making her one of the oldest and most complete human skeletons found in the Americas.

The chamber also held remains of at least 26 animal species from the last ice age. These included giant ground sloths, saber-toothed cats, gomphotheres, and an extinct bear species. A pelvic bone from one giant sloth measured about four feet wide and weighed roughly 80 pounds. Researchers dated the animal remains to about 15,000 years ago.

During the last ice age, sea levels were significantly lower than today, and the cave system was dry and open to the air. The deep pit served as a natural trap. Animals and humans could fall into it in the darkness. The chamber eventually flooded as glaciers melted and sea levels rose, sealing everything inside for thousands of years. Researchers date the flooding to roughly 8,000 to 12,000 years ago.

In 2014, genetic analysis of Naia’s remains, published in Science, linked her DNA to ancient populations who crossed the Bering land bridge from Asia into the Americas. This provided physical evidence supporting the established theory of early human migration into the continent.

The wider cave system, known as Sac Actun, spans hundreds of kilometers of mapped underwater passages beneath the Yucatán Peninsula. It is among the longest underwater cave systems documented. More than 220 sinkholes provide separate entry points to the network. Over nearly three decades, archaeologists have recovered human remains from at least 11 prehistoric burial sites within this system, along with numerous animal fossils and artifacts.

In early 2026, researchers announced the recovery of another human skeleton from the same cave network, found between Tulum and Playa del Carmen at a depth of about eight meters. Octavio del Río, the underwater archaeologist who led the recovery, said the location and depth suggested it was placed there when the cave was still dry. Analysis dated the remains to about 8,000 years old. The positioning suggested a deliberate burial, possibly associated with funerary rituals, rather than an accidental death. It was the eleventh prehistoric human skeleton recovered from the cave network.

The cave system continues to yield new discoveries. Recovering fossils from these depths requires highly trained cave divers working carefully to avoid disturbing sediment that can reduce visibility to zero. Each expedition depends heavily on professional diving skills given the dangerous environment.

The evidence gathered from Hoyo Negro and the broader cave system has helped researchers better understand how early humans migrated across the continent, adapted to different environments, and used underground water sources. The bones and artifacts also show that humans and ice-age animals shared these cave spaces over thousands of overlapping years.

Some popular accounts have claimed the cave was sealed for 40,000 years, but published research does not support that figure. The confirmed dates for human remains range from 12,000 to 13,600 years old, animal remains date to about 15,000 years, and the flooding occurred roughly 8,000 to 12,000 years ago. The broader debate about when humans first entered the Americas is separate and remains an active area of research, with most current estimates suggesting migration began at least 25,000 years ago.