Prehistoric wolf’s gut frozen in time reveals an ice age giant

By Katie Hunt, CNN

(CNN) — On the vast expanse of the Siberian steppe 14,000 years ago, a 2-month-old wolf pup gobbled down some woolly rhinoceros flesh. Moments later, its underground den collapsed, killing the pup and its sister.

The wolf’s stomach contents, frozen in permafrost along with its corpse, have allowed scientists to sequence the DNA of one of the last known woolly rhinos, a horned ice giant that lived alongside mammoths. Now, the findings from the wolf’s last meal are revealing clues about why the woolly rhino went extinct.

The research, which published Wednesday in the scientific journal Genome Biology and Evolution, represents the first time that scientists have been able to sequence the entire genome — the whole genetic code — of an animal found in the stomach of another animal, according to coauthor Camilo Chacón-Duque, a bioinformatician at the SciLifeLab Ancient DNA Unit at Uppsala University in Sweden.

“We were very excited because there are very little fossils from around this time when the woolly rhinoceros went extinct,” said Chacón-Duque, who was previously a researcher at the Centre for Palaeogenetics at the University of Stockholm, where the research was conducted.

Still covered in fur, the mummified wolf pup was found entombed in permafrost near the village of Tumat in 2011. An autopsy later uncovered a small fragment of preserved tissue in its stomach. Scientists were able to retrieve DNA from the tissue, which was 14,000 years old, and DNA sequencing revealed it was a species of woolly rhinoceros known as Coelodonta antiquitatis.

Chacón-Duque said hair on the woolly rhino tissue was still intact, suggesting the pup had barely begun digesting its meal before it died.

“From the morphological analysis, it seems to be clear that they were just buried alive. They just died in an instant, and that’s how it got to be preserved,” he said. “I think there was not enough time for the digestive system to really penetrate the tissues.”

The wolf cub’s sister was subsequently found in 2015, and neither showed signs of being attacked or injured. A study published last year noted they likely died when their underground den collapsed as a result of a landslide. That study suggested that wolves would have been able to hunt juvenile woolly rhinos. Adult woolly rhinos would have been similar in size to the largest living rhinoceros species.

With its long hair, the woolly rhino adapted to cold conditions and lived across northern Eurasia during the last ice age. Its range gradually contracted eastward starting 35,000 years ago, the study said, but it persisted in northeastern Siberia and had been assumed to have gone extinct sometime after 18,400 years ago.

While woolly rhino fossils are relatively common in the fossil record, few remains have been found from the estimated time of its extinction, and none have yielded genetic information, making the wolf’s stomach contents valuable to researchers.

Chacón-Duque said it was difficult to map the genome from the woolly rhino’s DNA sample because the presence of wolf DNA in the stomach complicated the analyses. For example, both the wolf and rhinoceros were equally old so they could not use patterns of degradation as a tool to identify the ancient DNA. Instead, Chacón-Duque and his colleagues used the woolly rhino’s closest living relative, the Sumatran rhino, as a guide.

Once they had sequenced the sample, they compared the genome with two other genomes sequenced from woolly rhino fossils found preserved in the Siberian permafrost, dated to 18,000 years ago and 49,000 years ago, respectively.

The permafrost preserves ancient DNA particularly well, and scientists have recovered DNA molecules dating back 2 million years from the planet’s northernmost reaches.

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 through time during the last ice age.

The study found no signs of genetic deterioration as the species approached extinction, suggesting the woolly rhinoceros probably maintained a stable and relatively large population until just before the species disappeared.

Its extinction must have happened relatively quickly, the researchers concluded, probably as the result of global warming at the conclusion of the last ice age, which ended around 11,000 years ago.

“Our results show that the woolly rhinos had a viable population for 15,000 years after the first humans arrived in northeastern Siberia, which suggests that climate warming rather than human hunting caused the extinction,” coauthor Love Dalén, professor of evolutionary genomics at the Centre for Palaeogenetics, said in a statement.

Previously, the two wolf pups had been thought to be early domesticated dogs or tamed 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 woolly rhinoceros, said Nathan Wales, a senior lecturer in archaeology at the UK’s University of York, who studied the wolf pups but wasn’t involved in the research on the woolly rhino sample.

“The researchers know that this species was nearing its extinction at that point in time, and one might assume the last lineages would have small populations and were highly inbred. But this well-established analysis shows that at a genetic level, the population looked stable,” he said via email.

“The authors have presented a reasonable conclusion that an outside factor, such as rapid environmental change drove extinction.”

Wales noted that plants, insects and a wagtail had also been found inside the wolf pups’ stomachs, and that it would be exciting to apply ancient DNA methods to these dietary contents as well.

“Permafrost mummies give a spectacular view into the past. Usually palaeontologists and archaeologists can only recover bones, but here we can better understand how these animals looked 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 analyses.”

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