Last month, researchers from the Great Maya Aquifer Project announced the discovery of the world's largest underwater cave system in Yucatán after realizing that two massive cave systems in the Mexican peninsula were connected. Now, they're unveiling the findings to the public.
"This immense cave represents the most important submerged archaeological site in the world," underwater archaeologist and National Geographic explorer Guillermo de Anda told National Geographic in January when the newly discovered system was announced. "It has more than a hundred archaeological contexts, among which is evidence of the first settlers of America, as well as the extinct fauna and, of course, of the Maya culture."
Researchers say the water level in the 215-miles-long Sac Actun cave system has likely fluctuated over time, providing a source of much-needed water during times of severe drought. For example, water levels rose more than 300 feet at the end of the Ice Age, flooding the cave system and preserving the remains of extinct megafauna. Humans likely didn't live in the caves, but probably visited them in search of water.
In the system, underwater archaeologists found the 15,000-year-old remains of giant sloths, proto-elephants called gomphotheres, and bears, as well as an elaborate shrine to the Maya god of war and commerce.
More than 120 artifact sites such as burnt human bones, ceramics, and wall etchings have been found in the caves, some dating back more than 12,000 years. One human skull covered in rainwater limestone deposits is 9,000 years old, de Anda says.
Archaeologists have been exploring these cave systems for decades, and these latest discoveries are consistent with the human artifacts and megafauna previously found in the Yucatán's watery underworld. The enormous length of the massive Sac Actun system makes these new discoveries particularly remarkable.
"It is very unlikely that there is another site in the world with these characteristics," de Anda says in a statement. "There is an impressive amount of archaeological artifacts inside, and the level of preservation is also impressive."
Even so, experts warn that the Sac Actun cave system is threatened by pollution.
Archaeologists study a colossal Olmec stone head in La Venta, Mexico in this 1947 National Geographic photo. The Olmec civilization, the first in Mesoamerica, offers valuable clues into the development of the rest of the region.