For thousands of years, Siberia’s Denisova Cave was home to various bands of Neanderthals, Denisovans, and modern humans. But as new research shows, animals occupied this cave more frequently than not, showcasing the pains, perils, and complexities of palaeolithic life.
“Basically, the story that we are telling is full of shit,” said Mike Morley, an archaeologist at Flinders University and the lead author of the new study, in an email to Gizmodo.
Well, to be fair to Morley and his colleagues, their story is also full of charcoal fragments, ash, bits of bone, and flakes from stone tools – all of which were dredged from 3 to 4 metres (9 to 13 feet) of sediment at the bottom of two chambers in Denisova Cave. By performing a micromorphological analysis of all the stuff embedded within this dirt – both geological and biological – the researchers were able to reconstruct a history of habitation in the cave over the course of 300,000 years, a timespan that included no less than three interglacial cycles. Their research is published today in Scientific Reports.
“Non-human animals were using the cave for much of its occupational history, and early humans were only occasional users.”
Denisova Cave, located at the foot of Siberia’s Altai Mountains, is famous for hosting two now-extinct hominin species: Neanderthals and Denisovans.
Earlier this year, an extensive survey of fossils and other evidence found in the cave traced the history of human occupation at the site, showing that Denisovans – a sister species to the Neanderthals – first ventured into this cave around 287,000 years ago, followed by their Neanderthal brethren around 140,000 years ago.
Genetic evidence from 2018 suggests the two groups cohabited and co-mingled in the cave, as evidenced by the discovery of a half-Denisovan, half-Neanderthal individual. Artifacts found in the cave dating to between 49,000 and 43,000 years ago are ambiguous in terms who produced them, though it’s highly likely they were left behind by modern humans, adding a third possible occupant of Denisova Cave. The last bits of definitive evidence from either Denisovans or Neanderthals stop around 52,000 years ago.
These timelines are extensive, encompassing literally hundreds of thousands of years. What these fossils and artifacts haven’t been able to tell us, however, is whether these hominin occupations were continuous or interrupted. The new research corroborates the previous work done in Denisova Cave, but it also helps to fill in some unknown gaps, showing that archaic humans were not present in the cave for significant swaths of time. In their place were several species of carnivorous animals, including hyenas, wolves, and sometimes even bears, according to the new research.
Flinders University archaeologist Mike Morley sampling sediment in Denisova Cave. Image: Mike Morley
“We already knew from the fossil bone record that other animals were present in the cave, but it was a surprise just how much hyena – and to a lesser extent, wolf – poop there would be in the sediment record,” said Morley. “It really shows that non-human animals were using the cave for much of its occupational history, and early humans were only occasional users.”
Indeed, the sheer volume of coprolites – the fancy archaeological term for fossilised poop – along with traces of animal bones within the various sedimentary layers suggests the cave was occupied by animals “near-continuously,” in the words of the authors, and that the cave was off limits to humans for extensive periods, though it’s not immediately obvious as to why. Importantly, there’s no evidence that humans came into conflict with these animals. That said, Morley said there’s “no doubt” competition existed for this precious space. The copious amounts of poop from “cave-dwelling carnivores is ubiquitous and suggests that the site often served as a den for hyenas and, to a lesser extent, for wolves,” the study authors wrote.
A block of dirt taken from Denisova Cave. Image: Mike Morley
At the same time, the “cave was visited sporadically by hominins, who appeared not to have been prolific users of fire,” according to the paper. This juxtaposition – lots of carnivores, few hominins, and little evidence of fire – means archaeologists should take extra caution in determining how human bones reached the bottom of the cave. As Morley pointed out to Gizmodo, some humans bones may have been brought into the cave by scavenging hyenas from the outside, so in some cases the presence of hominin fossils may not be indicative of hominin occupation at the site.
This new paper marks the first time that dirt from Denisova Cave has been analyzed in such fine detail. By doing so, Morley and his colleagues were able to detect materials in the sediment not normally visible to the naked eye, such as evidence of coprolites, small bits of bone, microscopic and macroscopic fragments of charcoal from fire pits, and traces of ash and flakes from stone tools.
To conduct the study, the archaeologists “removed blocks of sediment from the trench walls at the site and took them back to the laboratory,” said Morley. These blocks were then soaked in plastic resin for hardening, which allowed them to be cut into exceptionally thin slices, some measuring just 30 microns in depth. These slices were analysed with an optical microscope and a scanning electron microscope to “look for micro-traces of human and animal occupation,” along with features indicative of a changing climate, he said.
Microscopic images of coprolites (fossilised poop), including those from hyenas, wolves, and some unindentified species. Image: M. M. Morley et al., 2019/Scientific Reports
Indeed, the climate in the Altai mountains was not constant over the course of the 300,000 years studied. Broadly speaking, the climate “switched from cold and arid, open steppe environments during glacial periods to warmer and usually wetter periods with forest steppe during interglacial periods,” explained Morley. Neanderthals and Denisovans were probably well adapted to the cold weather, and both groups were likely living in the area even during the colder periods, said Morley.
Archaeologist Katerina Douka from the Max Planck Institute for the Science of Human History in Germany, who was not affiliated with the new research and is an expert on the Denisova Cave, said the new study is important because it provides “background information” about the stuff buried within the cave’s sediment.
“Studying the succession of layers at the microscopic level, it is amazing to discover a wide range of materials, from bone fragments to hyena coprolites and even stone tool chips,” Douka wrote to Gizmodo in an email. “It also indicates that humans and animals would alternate as the site’s occupants, highlighting how challenging and precarious life was in the Palaeolithic period.”
Indeed, the new paper raises some important questions about both Denisovans and Neanderthals in the area, such as why they only lived here sporadically and how the presence of other, potentially dangerous animals influenced their movements. Denisova Cave continues to intrigue, and it undoubtedly has more stories to tell.
Featured image: Mike Morley