Five species of rhinoceroses exist today, but the lumbering creatures were once far more plentiful; palaeontologists have identified 250 species that historically roamed throughout Africa, Eurasia and North America. Among them was the great Elasmotherium sibiricum, known as the “Siberian unicorn” for the huge horn that protruded from its skull. Scientists long believed that E. sibiricum died out between 100,000 and 200,000 years ago, but as Natasha Frost reports for Quartz, a new study has found that the hulking unicorn actually survived until about 39,000 years ago, which places it roaming alongside modern humans and neanderthals.
E. sibiricum was a tremendous animal, and a strange one. It weighed around 3.5 tons, but in spite of its massive heft, it had relatively slender limbs, suggesting it was an adept runner. Its body was covered in shaggy hair, and the horn that jutted out from its skull was the largest of any known rhinoceros species, living or extinct. The geographic range of E. sibiricum appears to have been relatively limited; its fossils have been found primarily in Kazakhstan, western and central Russia, Ukraine, Azerbaijan and Uzbekistan.
Previous research has suggested that the commonly accepted timeline of E. sibiricum’s extinction might be off by tens of thousands of years. In 2016, for example, an E. sibiricum skull found in Kazakhstan was radiocarbon dated to 29,000 years ago. A complete skull held by the Natural History Museum in London was found to be less than 40,000 years old. But these findings, based on individual fossils, were not conclusive.
The new study, published in the journal Nature Ecology & Evolution, took a more comprehensive look at a range of Siberian unicorn specimens. Scientists from the Netherlands, Russia and the United Kingdom analyzed fossils from 23 E. sibiricum individuals. According to Gizmodo’s George Dvorsky, many of the specimens had been covered in preservation materials, requiring the researchers to use advanced dating techniques.
“Some of the samples we studied were very contaminated which made the radiocarbon dating very challenging,” explains Thibaut Devièse, study co-author and principal investigator at Oxford University’s Radiocarbon Accelerator Unit. “For this reason we used a novel method of extracting a single amino acid from the bone’s collagen in order to ensure highly accurate results.”
The team’s findings suggest that E. sibiricum was still alive 39,000 years ago—and possibly as recently as 35,000 years ago. This in turn places the Siberian unicorn’s extinction within a period known as the “Quaternary extinction event,” which saw the mass die-offs of ancient megafauna like the woolly mammoth, Irish elk and sabre-toothed cat.
“This megafaunal extinction event didn't really get going until about 40,000 years ago,” says Adrian Lister, a study co-author and a researcher at the Natural History Museum in London. “So Elasmotherium, with its apparent extinction date of 100,000 years ago or more, has not been considered as part of that same event.”
The new date for E. sibiricum’s demise also suggests that it overlapped in time with Neanderthals and early modern humans. But according to the study authors, human hunters were likely not the cause of the animal’s extinction.
By studying stable isotopes in fossilized E. sibiricum teeth, the researchers were able to determine that the rhinoceros fed almost exclusively on tough, dry grasses. But in the lead up to the Last Glacial Maximum, when the world’s ice sheets reached their greatest extent around 27,000 years ago, E. sibiricum’s habitat started to change. Temperatures dropped and the grounds on which the animal grazed froze over, reducing the amount of available grass. Because its feeding habits were highly specialized, E. sibiricum eventually went extinct; other species that had a more flexible diet, like the woolly rhino, were able to survive for another 20,000 years.
The researchers behind the new study also extracted and analyzed DNA from some of the fossilized specimens, marking the first time that genetic material has been recovered from E. sibiricum. The team determined that the Elastrotherium genus split from the ancestors of living rhinos around 43 million years ago. “That makes the Siberian unicorn and the African white rhino even more distant cousins than humans are to monkeys,” says study co-author Kieren Mitchell, a post-doctoral research associate at the University of Adelaide.
The Siberian unicorn was the last surviving member of the Elastrotherium genus, and its death brought an end to a unique rhinoceros family. But as the new research suggests, the Elastrotherium line may have continued much longer than scientists previously believed.