March 17 (UPI) -- A study published Tuesday on mysterious bone circles on the Central Russian Plain, made largely from mammoth bones, reveals hints at how people survived Europe's ice age.
The study, published in the journal Antiquity, uses radiocarbon dating and extraction by flotation of charcoal and chipped stone to show the oldest bone circle built by humans at one site on the Russian Plain.
The site, just outside of the modern village of Kostenski, 300 miles south of Moscow, is known as Kostenski 11.
Bones at the site are more than 20,000 years old, which means the Kostenski site was being built as the Ice Age reached its coldest stage -- where summers were short and winters were long, with temperatures around -4 degrees Fahrenheit or colder.
The bone circle is a foot below current surface level, and the bones were likely sourced from animal graveyards and hidden by sediment, the analysis suggests.
The majority of bones were from mammoths. Fifty-one lower jaws of mammoths and 64 mammoth skulls were used to construct the walls of the 30-foot by 30-foot structure and scattered across the interior. Other bones were found in smaller numbers, including bones of reindeer, horse, bear, wolf, red fox and arctic foxes.
About 70 bone circle structures are known to exist in Ukraine and the Russian Plain, according archaeologists at University of Exeter who conducted the research. Eventually the bone circles were abandoned as the climate got colder and more inhospitable.
Archaeologists also for the first time found remains of charred wood and plant remains that showed ancient communities were burning wood, along with bones, for fuel and foraging for edible plants.
Researchers said the plants could have also been used for poisons, medicines, string or fabric.
Archaeologists had previously assumed the mammoth bone circles were used as dwellings for many months, but the new research shows the intensity of activity was less than would be expected from a long term base camp site.
"Kostenski 11 represents a rare example of Paleolithic hunter gatherers living on in this harsh environment," said Dr. Alexander Pryor, who led the study. "What might have brought ancient hunter gatherers to this site? One possibility is that the mammoths and humans could have come to the area on masse because it had a natural spring that would have provided unfrozen liquid water throughout the winter -- rare in this period of extreme cold."
"These finds shed new light on the purpose of these mysterious sites," Pryor added. "Archaeology is showing us more about how our ancestors survived in this desperately cold and hostile environment at the climax of the last ice age. Most other places at similar latitudes in Europe had been abandoned by this time, but these groups had managed to adapt to find food, shelter and water."