Bones in underwater cave on Yucatan are around 13,000 years old

Exciting find: In an underwater cave in Mexico, archaeologists have discovered the perhaps oldest human remains of America. The bone remnants half enclosed in a stalagmite could already be 13,000 years old, as uranium thorium dating suggests. Bizarre: The complete skeleton was discovered by cave divers already in 2012, but the majority of it was stolen shortly thereafter.

Skulls and bones of the "Ancient-American" in the underwater cave of Chan Hol - before they were stolen. © Tom Poole, Liquid Junge Lab

When the first people entered the American continent is still unclear - and controversial. According to current opinion, immigrants from Siberia moved about the Bering Land Bridge to North America about 15,000 years ago and spread along the coast and through an ice-free corridor to the south. How quickly this colonization took place - and whether this estimate of time is at all true - is disputed. Human fossils from this period are extremely rare.

Skeleton found in underwater cave

All the more exciting is a discovery in Mexico: In February 2012, cave divers had discovered the remains of a prehistoric man in a water-filled cave near Tulum. The almost complete skull and some skeletal bones lay in the middle of the drip-stones of the Chan Hol cave. Because of the karst traversed by cavities in this area during the ice age was still above the water level, the cave was not flooded and drip-stones could arise.

Inspired by their find, the cave divers posed in front of the skeleton in the social media - with fatal consequences. For when archaeologists a month later dived into the cave to examine and recover the remains, the skeleton had disappeared. Apparently inspired by the posts, strangers had stolen the valuable find.

Pelvic bones in the stalagmites

But fortunately for the archaeologists, the thieves had not caught all the bone parts:

About ten percent of the skeleton have remained on site, report Wolfgang Stinnesbeck from the University of Heidelberg and his colleagues.

Among the fragments was also a piece of the pelvic bone, which had grown half into a stalagmite.

This probably prevented this bone from being stolen, says Stinnesbeck.

From the analysis of the bone fragments, the researchers conclude that the dead man must have been a young man. He must have been there before flooding the cave, otherwise its bones would not be enclosed by the stalagmites. Perhaps the man died at the time or was buried in the Chan Hol Cave.

How old is the dead?

But the big question was: When was that? How old the remnants are, scientists would normally be determining by means of radiocarbon dating. But because the bones were so long in the water, almost all the organic constituents are washed out. Stinnesbeck and his colleagues used a dating specifically for minerals: the analysis of the uranium and thorium isotopes.

The highlight: Because the pelvic bone of the dead was partially enclosed by a stalagmite, the age of the dripstone could also be "lying" about the age of the bone. The researchers analyzed the layers of the stalagmite arranged as annual rings. The ratio of the uranium and thorium isotopes in the calcite rock showed that the layer had to be at least 11.300 years old. Immediately on the bone, however, the analyzes revealed uneven results, as archaeologists admit.

One of the earliest Americans

The researchers assume, however, that the skeleton must be at least 13,000 years old.

We are sure that our age determination is quite accurate and that this pelvic bone could be 13,000 years old, says Stinnesbeck and his colleagues.

Thus, the remains of the young man could be among the oldest known on the American continent.

However, recently, researchers have discovered that perhaps there were already very early people in the New World. For example, blade traces on bones in Alaska could already be 24,000 years old and processing traces on mastodon bones could already be 130,000 years - if these traces actually originate from humans.

Source: PLOS ONE, 2017; doi: 10.1371 / journal.pone.0183345