Divers exploring Mexico’s underwater caves uncover rarely seen artifacts, fossils, and human remains. The cenotes of the Yucatán Peninsula serve as time capsules, preserving remnants of Maya culture and fossils of extinct megafauna.
These underwater caves offer a glimpse into the distant past, having transformed over two million years through multiple glaciation cycles. When sea levels were high, the caves flooded and expanded. During ice ages, the caves dried out as sea levels dropped, allowing water from the surface to decorate the caverns with speleothems like stalagmites and stalactites. Subsequent cycles of rising sea levels flooded the caves again, preserving these formations and everything within them.
Having dived in the unique submerged landscapes of Mexican cenotes for nearly a decade, I’ve explored their dark, flooded tunnels and uncovered their secrets. The last time the shallow caves of the Yucatán Peninsula flooded was around 8,000 years ago, making each dive a journey back to a prehistoric age. The paleontological and archaeological remains preserved in these caves would disintegrate at the surface, making them perfect time capsules.
The Formation of Mexico’s Cenotes
This underworld is formed by a massive underground aquifer in the northern Yucatán Peninsula. Cenotes connect the surface to the world’s longest underground river systems. Instead of accumulating on the surface as rivers, water is absorbed through porous limestone, flowing within underground tunnels. These tunnels, much like blood vessels, convey the precious water that sustains all life in the region, which is why cenotes were sacred to the Maya.
The Maya civilization, established on the Yucatán Peninsula about 4,000 years ago, thrived by settling close to freshwater sources. Their largest settlements, including Chichén Itzá, were built beside cenotes. During the dry season, cenotes were the only water source, making them fundamental to Maya life and a place for worship and rituals related to rain, life, death, and rebirth.
Each Maya d’zonot (the origin of the word cenote) was an entrance to the mystical underworld called Xibalba, home to various deities and supernatural beings. This powerful realm, associated with death, was a portal where ritualistic offerings honored both gods and the deceased, seeking protection and guidance for the living. Chaac, the god of rain, fertility, and agriculture, was the protector of this underworld, vital for the success of crops and community well-being.
Beneath the cenotes, deeper in their caves, artifacts and human remains from the Maya civilization have lain undisturbed for centuries, visible to explorers. Evidence found in the cenotes also points to human settlements in the area dating back more than 13,000 years, challenging the accepted timeline of when our ancestors first crossed into America via the Bering Land Bridge during the last ice age.
These ancient hunter-gatherers relied on the cenotes for water and possibly for shelter. Back then, the cenotes were much drier, with water levels about 300 feet below today’s levels. To access water, the ancient inhabitants had to venture deep into the caves, often encountering huge prehistoric animals from the late Pleistocene, now long extinct, that also sought fresh water.
Encountering a human skull in the darkness of the flooded caves evokes a raw and profound sensation. Before recognizing it as mere remains, I can feel its gaze from the shadows, a haunting presence that defies description. In the Ring of Cenotes, many sacrificial cenotes contain skulls of higher-ranking Maya families. These skulls, with modified front teeth for ornaments, were artificially deformed to create a distinct appearance. The higher-ranking Maya shaped their children’s skulls to create an oblique deformation, making their heads look longer, resembling a jaguar’s head—a symbol of power. Rare sightings for cave explorers include sophisticated Maya paintings on cave walls near cenote entrances, depicting wars, animals, gods, and stories. These treasures risk being lost forever once submerged and washed away over time.
Long before the Maya settled the area, the first Homo sapiens crossed into America over the Bering Land Bridge at least 25,000 years ago. They traveled down to South America and arrived on the Yucatán Peninsula around 13,000 years ago, at the end of the last ice age. They used the caves to extract water and minerals, find shelter, and bury their dead. While remains of these hunter-gatherers are hard to find on the Earth’s surface, evidence of early human presence is preserved in these caves from before the last flooding, offering clues to early human biology and social interactions.
Within the flooded caves, it is common to see purposely broken formations creating passages through the tunnels and cairns—piles of rocks or broken speleothems—placed at tunnel junctions to navigate the intricate cave labyrinths. Early humans also excavated rocks and mined red ocher using Stone Age tools and their mastery of fire. They used ocher to decorate objects for personal ornamentation and burials and decorated the caves with various art forms, from paintings on the walls to sculptures. A well-known example is the figure of a woman at the entrance of Cenote Dos Ojos; while not sculpted, it is a carefully selected speleothem resembling a woman’s silhouette, intentionally exhibited on a pedestal to decorate the cave entrance, evidence of paleoart from over 8,000 years ago that anyone can visit.
The submerged passageways of these time capsules, like museum corridors, offer divers the chance to uncover exquisitely preserved fossils of diverse creatures—most now extinct—that once inhabited the Yucatán during the late Pleistocene.
Following the Chicxulub asteroid impact 66 million years ago, which ended the dinosaur age, mammals began to dominate the lands once ruled by dinosaurs. Over time, North and South America underwent distinct evolutionary paths. However, around 2.7 million years ago, the formation of the Panamanian land bridge facilitated the Great American Biotic Interchange.
During this exchange, North American fauna migrated southward, including large mammals known as megafauna, such as saber-toothed cats, lions, gomphotheres (relatives of modern elephants), horses, and camels. Meanwhile, South American megafauna moved northward, including giant ground sloths and glyptodonts (enormous armadillos). This monumental event significantly shaped the ecosystems and biodiversity of both continents, influencing the species composition we see today.
Exploring the underwater caves of the Yucatán is thrilling, especially when uncovering the fossilized remains of these long-extinct megafauna. Visualizing these colossal creatures coming to life where you are diving, in what was once a prehistoric cave frozen in time by these waters, feels like being teleported back to their era. With water levels during the last ice age up to 300 feet lower than today, these animals had to venture deep into dark, dry cave passages to reach drinking water, sometimes far from an entrance. Trapped in sinkholes or lost within labyrinthine passages, these animals died, and their remains became fossilized and preserved by rising water levels.
Among the many extinct species that lived in this region are members of the family Megalonychidae, including the genus Megalonyx (Greek for “large claw”). Fossils of these giant ground sloths are commonly found in the caves, as they likely took refuge within them. This includes members of the genus Xibalbaonyx (“great claw of Xibalba”), a polar bear-sized ground sloth with big claws that measured up to 12 feet in height and weighed nearly a ton. They are joined by members of related families, such as the genus Nothrotheriops, a grizzly bear-sized mammal that reached five feet tall and weighed 1,000 pounds.
The fossils concealed within the caves represent archaeological and paleontological marvels, allowing specialized scientists to explore these wonders, unravel scientific enigmas, construct hypotheses, and shed light on the mysteries of our planet’s history.
Many More Mysteries to Be Solved
There’s a symbiotic relationship between passionate and technical cave explorers, who investigate every hole in a cave in their free time, and the scientific community, who want to study these prehistoric materials but cannot reach them in the underwater darkness. This relationship of discovery and research has already provided evidence of many newly discovered extinct species, as well as ancient humans who had vanished for millennia. This relationship could be fostered even more by leveraging the world-class level of dive explorers in the area. After all, the majority of these secrets remain yet to be discovered!
The caves also hold evidence that could solve a prehistoric murder mystery. After the Great American Biotic Interchange, these megafauna species coexisted in this region for hundreds of thousands of years and through multiple ice age cycles, until their abrupt extinction more than 10,000 years ago when a new species arrived on the Yucatán Peninsula: Homo sapiens.
After humans arrived in the region, many genera of large mammals became extinct. One leading hypothesis states that the already reduced populations of those animals, stressed due to the changing climate after the latest ice age, were hunted to extinction by humans. These big mammals, which needed a long time to become sexually mature and had slow reproduction rates (up to 22 months), were particularly vulnerable to this new threat.
Among the fossils preserved within the flooded caves, I have seen many examples suggesting that these extinct species were hunted and eaten by our predecessors. These include megafauna bones with cut marks from human-made stone tools, indicating methodical flesh removal, and perforations on fossilized bones caused by projectiles. Additionally, there are extinct animal remains beside cooking pits, organized piles of bones, and burn marks on fossils inside the cave. Such evidence has been found at cave depths corresponding to the time when humans and these now-extinct animals coexisted, alongside signs of sophisticated social organization, like the mining of red ocher.
While the hypothesis that Paleo-Americans overhunted these species to extinction still needs validation, it is undeniable that these caves protect invaluable material for scientists. This information helps us understand our past and can hopefully inform our future.
Source: Smithsonian Mag
