On the vast expanse of the Siberian steppe, 14,000 years ago, a 2-month-old wolf cub swallowed some woolly rhinoceros meat. Moments later, its underground burrow collapsed, killing the cub and its sister.
The contents of the wolf’s stomach, frozen in the permafrost along with its carcass, have allowed scientists to sequence the DNA of one of the last known woolly rhinoceroses, a horned ice giant that lived alongside mammoths. Now, discoveries from the wolf’s last meal reveal clues as to why the woolly rhino went extinct.
The research, published Wednesday in the scientific journal Genome Biology and Evolution, marks the first time scientists have been able to sequence the entire genome — the entire genetic code — of an animal found in another animal’s stomach, according to co-author Camilo Chacón-Duque, a bioinformatician at the SciLifeLab Ancient DNA Unit at Uppsala University in Sweden.
“We were very excited because there are very few fossils from this time when the woolly rhino went extinct,” said Chacón-Duque, who was previously a researcher at the Center for Paleogenetics at Stockholm University, where the research was conducted.
Still covered in fur, the mummified wolf cub was found buried in permafrost near the village of Tumat in 2011. An autopsy later revealed a small fragment of preserved tissue in its stomach. Scientists were able to extract DNA from the tissue, which was 14,000 years old, and DNA sequencing revealed it to be a species of woolly rhinoceros known as Coelodonta antiquitatis.
The piece of rhinoceros woolly tissue found in the wolf pup’s stomach. The hair is still attached. – Loves Dalén
Chacón-Duque said the hair on the rhino’s woolly tissue was still intact, suggesting the cub had only just begun to digest its food before it died.
“From the morphological analysis, it seems clear that they were buried alive. They died in an instant and that’s how it ended up being preserved,” he said. “I think there wasn’t enough time for the digestive system to really penetrate the tissues.”
The wolf cub’s sister was later found in 2015 and none showed signs of being attacked or injured. A study published last year noted that they likely died when their underground den collapsed following a landslide. That study suggested that wolves may have been able to hunt young woolly rhinos. Adult woolly rhinos would have been similar in size to the largest living rhinoceros species.
With its long hair, the woolly rhinoceros adapted to cold conditions and lived in northern Eurasia during the last ice age. Its range gradually contracted eastward starting 35,000 years ago, according to the study, but it persisted in northeastern Siberia and was thought to have disappeared sometime after 18,400 years ago.
A woolly rhinoceros preserved in permafrost on display at the museum in Yakutsk, Russia. – The North-Eastern Mammoth Museum
While woolly rhinoceros fossils are relatively common in the fossil record, few remains have been found from the estimated time of its extinction, and none have provided genetic information, making the wolf’s stomach contents valuable to researchers.
Chacón-Duque said it was difficult to map the genome from the woolly rhinoceros DNA sample because the presence of wolf DNA in the stomach complicated the analyses. For example, both the wolf and the rhinoceros were equally ancient, so they could not use decay patterns as a tool to identify ancient DNA. Instead, C hacón-Duque and his colleagues used the woolly rhinoceros’ closest living relative, the Sumatran rhinoceros, as a guide.
Once they sequenced the sample, they compared the genome to two other genomes sequenced from woolly rhinoceros fossils found preserved in Siberian permafrost, dated to 18,000 and 49,000 years old, respectively.
Permafrost preserves ancient DNA particularly well, and scientists have recovered DNA molecules dating back 2 million years from the northernmost areas of the planet.
The three genomes allowed the researchers to examine how the species’ genetic diversity, such as levels of inbreeding and the number of harmful mutations, changed over time during the last ice age.
The study found no signs of genetic deterioration as the species neared extinction, suggesting that the woolly rhinoceros probably maintained a stable and relatively large population until just before the species went extinct.
Its disappearance must have occurred relatively quickly, the researchers concluded, probably as a result of global warming at the end of the last ice age, which ended about 11,000 years ago.
“Our results show that woolly rhinos had a viable population for 15,000 years after the first humans arrived in northeastern Siberia, suggesting that climate warming, rather than human hunting, caused the extinction,” co-author Love Dalén, professor of evolutionary genomics at the Center for Paleogenetics, said in a statement.
Previously, the two wolf cubs had been thought to be early domesticated dogs or domesticated wolves. However, the 2025 study said there was no evidence the two animals had come into contact with humans.
The work was “extremely valuable” for understanding the evolutionary history of the woolly rhino, said Nathan Wales, a senior lecturer in archeology at the University of York in Britain, who studied the wolf cubs but was not involved in the research on the woolly rhino sample.
“Researchers know that this species was nearing extinction at the time, and one might assume that the last lineages would have small populations and were highly inbred. But this well-established analysis shows that at the genetic level, the population appeared stable,” he said by email.
“The authors presented a reasonable conclusion that an external factor, such as rapid environmental change, caused the extinction.”
Wales noted that plants, insects and a wolf tail were also found in the wolf pups’ stomachs, and that it would be interesting to apply ancient DNA methods to these food contents as well.
“Permafrost mummies offer a spectacular view of the past. Usually paleontologists and archaeologists can only recover bones, but here we can better understand what these animals looked like and lived,” he said. “Traces of their diets, microbiomes and ecosystems are directly associated with these mummies, so they hold a special role for scientific analysis.”
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