In February 2012, researchers discovered a human skeleton in
an underwater cave in Mexico. Their joy, however, was short-lived.
Just days after photos were made public, unknown divers plundered
the cave, stealing the complete skeleton and everything else they
could find. They were never identified, the skeleton never located.
Still, researchers managed to date a bone, based on measurements
conducted on a stalagmite in the cave. The research findings have
now been published in PLoS
human skeleton in the Chan Hol Cave near Tulúm on the
Yucatán peninsula prior to looting by unknown cave
divers. Picture: Tom Poole, Liquid Jungle Lab.
Settling a settlement debate
The earliest settlement in North America is still a matter of
debate among anthropologists and archaeologists. The classical hypothesis
is that the first migration took place 12,600 years ago through
an ice-free corridor between retreating North American glaciers,
over the Bering Strait which was still covered by an ice. That hypothesis
is recently coming
under more and more fire, with evidence from both
North and South America suggesting that a migration took place
earlier. However, that evidence is mostly hearths and artifacts
it"s extremely rare to find any human skeletons older than
10,000 years in the Americas. This is why this particular finding
might be so important.
"The bones from the Chan Hol Cave near the city of Tulúm
discovered five years ago represent one of the oldest finds of
human bones on the American continent and are evidence of an unexpectedly
early settlement in Southern Mexico," says Prof. Wolfgang Stinnesbeck,
who is an earth scientist at Heidelberg University.
The skeleton was found in a vast system of underwater carbonate
bedrock caves filled alternatively with salt and sweet water. These
caves, located near Tulúm
on the Yucatán Peninsula, have proven a valuable trove
for researchers. They contain archaeological, palaeontological and
climatic information hidden there from the time before the flooding,
which is extremely well preserved, according to Stinnesbeck.
When my Mexican colleagues Arturo Gonzalez and Jerónimo
Avilés showed me the first photos of the Chan Hol site,
I immediately knew that we had something special," says
This is why, when the skeleton was stolen, it hurt even more.
But scientists didn"t give up. They still had one bone to analyze
a pelvic bone that had since grown a stalagmite, a rock formation
rising from the floor of a cave due to material deposited on the
floor from ceiling drippings. Stalagmites are the floor counterpart
of ceiling stalactites.
ancient pelvis, as indicated by the orange arrow. Image credits:
Left them a bone
Dating the bone was no easy feat, for all the potential it yielded.
Bones this old have no more collagen, which is what is commonly
used for dating bones. So instead, researchers took a different
route: they dated it like a rock, not like a bone something
which was possible only thanks to the unique environment of the
bone. They used the uranium, carbon, and oxygen isotopes in the
bone itself and in the stalagmite that had grown through it. They
then analyzed the oxygen and carbon isotope ratios, which are directly
related to climate and precipitation data. This can be correlated
to existing data, so the age of the stalagmite was estimated, and
from it, the age of the bone. Researchers say it is at least 13,000
years old, which would add another nail in the coffin of the classic
More evidence would likely settle this debate once and for all,
since this is still an indirect dating method, and more evidence
likely lies in or around the cave system. But the area is threatened
by growing tourism and urbanization in the area. It"s no coincidence
that the skeleton was stolen after only a few photos, and researchers
fear what is to happen to the cave if it is left unprotected. Whatever
evidence may lie there could be gone forever.
This study fits in neatly with previous findings from the Paisley
Cave in Oregon and Monte
Verde, Chile, where there is evidence of early settlements.
Wolfgang Stinnesbeck et al The earliest settlers of Mesoamerica
date back to the late Pleistocene.