Tens of thousands of years ago, if you happened to be trekking across Ukraine toward the West Russian Plains, you might have come across a jaw-dropping scene.
Literally — lower jaws, entire skulls and other bones from woolly mammoths were perfectly arranged into circular structures.
In recent years, scientists have managed to dig up 70 of these strange and surreal bone rings.
But this week, researchers announced that one Russian site, dubbed Kostenki 11, features bones that are at least 20,000 years old.
The new analysis, published in the scientific journal Antiquity, marks Kostenki 11 as the oldest of the circle structure built by Ice Age humans in the region.
A total of 51 lower jaws and 64 individual mammoth skulls were used to construct the walls of the 80 square meter structure and scattered across its interior.
But more importantly, it may offer clues about how humans managed to survive the Pleistocene Epoch — a time when homo sapiens shared a rapidly changing planet with the likes of saber-toothed cats, mastodons and giant ground sloths.
By the end of that cold, barren stretch, roughly 11,700 years ago, humans emerged as the dominant player on the planet.
But what do these old bone circles tell us about how they not only survived the Ice Age, but thrived?
"Kostenki 11 represents a rare example of Palaeolithic hunter-gatherers living on in this harsh environment," the study's lead author, Alexander Pryo notes in a press release. "What might have brought ancient hunter-gatherers to this site?
"One possibility is that the mammoths and humans could have come to the area en masse because it had a natural spring that would have provided unfrozen liquid water throughout the winter — rare in this period of extreme cold."
The ancient bones point to still other possibilities. The walls of the Kostenki structure were made from 51 lower jaws and 64 individual mammoth skulls, spanning some 860 square feet.
It's long been thought that these structures served as a kind of housing for ancient humans. At the Kostenki site, researchers found charred wood which, along with the bones, may have been burned for fuel. Researchers also found evidence of plants at the site, pointing to what may have sustained residents. They may have also used plants to make poisons, medicines, string and fabrics.
As for the mammoth bones, researchers say it's unlikely the animals were hunted and killed to build the structure.
Instead, the bones were likely sourced from mammoth graves. The Arctic circle was once teeming with these wooly behemoths. In fact, with today's melting permafrost, increasing numbers of mammoth tusks have been spotted poking out the receding ground — creating an unlikely tourism industry in the region.
But mammoths weren't the only animals present in the eerie architecture. Researchers found the remains of reindeer, horses, bears, wolves and red and Arctic foxes.
"These finds shed new light on the purpose of these mysterious sites," Pryor adds. "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."
The idea may have been that these bizarre bone residences were not only built to withstand extreme Ice Age conditions — but also safe spaces where homo sapiens could develop tools and technologies to help them eventually emerge as a force in the brave new post-Ice Age world. A cradle, if you will, of civilization. Only crafted in bone.
You can learn more about these fascinating bone homes in the video below: