Ice Age fossils in cenotes

Why cenotes hold Ice Age bones

During the last Ice Age, sea levels were about 120 m lower (reported), so the Yucatán's caves were dry. Animals went in for water or shelter, or fell through holes in the roof, and died. As the ice melted, seas rose and the caves flooded about 8,000 to 10,000 years ago (reported), sealing the bones under water.

Why the bones survived

• Dark, calm water with little oxygen slows decay.
• No scavengers or rain to move bones.
• Stable temperature year-round.
• Bones can lie untouched for over 10,000 years until divers find them.

Animals found

• Giant ground sloths, including a species named after the Yucatán (reported).
• Gomphotheres, elephant relatives.
• Saber-tooth cats (reported).
• Short-faced bears (Arctotherium) at Hoyo Negro (reported).
• Ancient horses, camels' relatives, tapirs and peccaries (reported).
• Bats, birds and small mammals.

Hoyo Negro and Naia

Hoyo Negro is a huge flooded pit in the Sac Actun system near Tulum, about 55 m deep (reported). In 2007 divers found the skeleton of a teenage girl, named Naia, plus the bones of many Ice Age animals. Naia is reported to be about 12,000 to 13,000 years old, one of the oldest nearly complete human skeletons in the Americas.

Other human remains

Other very old human skeletons have been reported in the Tulum caves, such as the 'Woman of Naharon' and remains from Chan Hol cave. Some studies suggest even older ages, but these are debated (reported).

Who studies the fossils

• Mexico's INAH, which protects all finds.
• Cave-diving researchers and universities.
• Projects like the Gran Acuífero Maya (GAM).

Can visitors see them?

Mostly no. The fossils lie deep inside flooded caves reached only by trained cave divers with permits. Touching or taking bones is illegal.

Naia: the girl from Hoyo Negro

In the flooded Hoyo Negro pit, part of the Sac Actun system, cave divers found the skeleton of a teenage girl now called Naia. She lived about 13,000 years ago and is one of the oldest and most complete human skeletons found in the Americas. Her bones helped link the first Americans to living Native American peoples.

Animals found with her

The same pit held bones of extinct animals, including ground sloths, a gomphothere (an elephant relative) and extinct bears and big cats. Some show that animals moved between North and South America after the land bridge at Panama formed.

Why caves preserve bones so well

The caves were dry during the ice ages, so people and animals walked in and sometimes fell into pits. When sea levels rose, the caves flooded with still, low-oxygen water that slowed decay and protected the bones for thousands of years.

Can tourists see fossils?

Not in the water: finds are protected and only studied by permitted scientists. Some museums in Mexico display replicas and explain the discoveries. Never touch or remove bones if you see anything while diving.