New research has shed light on the origin and extinction of a giant, shaggy Ice Age rhinoceros known as the Siberian unicorn because of its extraordinary single horn.
An international team of researchers from Adelaide, Sydney, London, the Netherlands, and Russia, have settled a long-standing debate about the relationship of the Siberian unicorn to living rhinos, and revealed that it survived much later than previously believed, overlapping in time with modern humans.
Published in the journal Nature Ecology and Evolution and led by London's Natural History Museum, the researchers say the Siberian unicorn became extinct around 36,000 years ago. This was most likely because of reduction in steppe grassland where it lived – due to climate change rather than the impact of humans.
Today there are just five surviving species of rhino, although in the past there have been as many as 250 species.
Weighing up to 3.5 tonnes with a single enormous horn, the Siberian unicorn (Elasmotherium sibiricum), which roamed the steppe of Russia, Kazakhstan, Mongolia, and Northern China, was undoubtedly one of the most impressive.
Genetic analyses performed at the University of Adelaide's Australian Centre for Ancient DNA (ACAD), however, have shown that the Siberian unicorn was the last surviving member of a unique family of rhinos.
"The ancestors of the Siberian unicorn split from the ancestors of all living rhinos over 40 million years ago," says co-author and ACAD researcher Dr. Kieren Mitchell, who analysed the DNA of the Siberian unicorn. It is the first time DNA has ever been recovered from E. sibiricum.
"That makes the Siberian unicorn and the African white rhino even more distant cousins than humans are to monkeys."
This new genetic evidence overturns previous studies that suggested the Siberian unicorn was a very close relative of the extinct woolly rhino and living Sumatran rhino.
It had long been assumed that the Siberian unicorn went extinct well before the last Ice Age, perhaps as much as 200,000 years ago.
In this study 23 Siberian unicorn bone specimens were dated, confirming that the species survived until at least 39,000 years ago, and possibly as late as 35,000 years ago. The Siberian unicorn's final days were shared with early modern humans and Neanderthals.
"It is unlikely that the presence of humans was the cause of extinction," says co-author Professor Chris Turney, climate scientist at the University of New South Wales.
"The Siberian unicorn appears to have been badly hit by the start of the ice age in Eurasia when a precipitous fall in temperature led to an increase in the amount of frozen ground, reducing the tough, dry grasses it lived on and impacting populations over a vast region."
Other species that shared the Siberian unicorn's environment were either less reliant on grass – like the woolly rhino – or more flexible in their diet – like the saiga antelope – and escaped the Siberian unicorn's fate, though the woolly rhino eventually became extinct 20,000 years later.
Explore further: When did the 'Siberian unicorn' disappear?
Pavel Kosintsev et al. Evolution and extinction of the giant rhinoceros Elasmotherium sibiricum sheds light on late Quaternary megafaunal extinctions, Nature Ecology & Evolution (2018). DOI: 10.1038/s41559-018-0722-0