Stomach of a prehistoric wolf frozen in time reveals an Ice Age giant

14,000 years ago in the vast expanses of the Siberian steppe, a 2-month-old wolf pup chowed down some woolly rhinoceros meat. Moments later, its underground den collapses, killing the dog and its sister.

The contents of the wolf’s stomach, frozen in permafrost along with its carcass, have allowed scientists to sequence the DNA of one of the last known woolly rhinoceroses, a one-horned ice giant that lived with mammoths. Now, the discovery of the wolf’s last meal is revealing clues about why the woolly rhino went extinct.

The research was published Wednesday in the scientific journal Genome Biology and Evolution, It represents the first time scientists have been able to sequence the entire genome — the entire genetic code — of an animal found in another animal’s gut, according to coauthor Camilo Chacon-Duc of the SciLifeLab Ancient DNA Unit at Uppsala University in Sweden.

“We were very excited because there are very few fossils from when the woolly rhinoceros went extinct,” said Chacon-Duc, a researcher at Stockholm University’s Center for Paleogenetics, where the research was conducted.

Still covered in fur, a mummified wolf pup was found in permafrost near the village of Tumat in 2011. A later autopsy found a small piece of preserved tissue in its stomach. Scientists were able to recover DNA from the 14,000-year-old tissue, and DNA sequencing revealed that it was a species of woolly rhinoceros known as Colodonta antiquititis.

Chacon-Duc said the woolly rhinoceros had hairs still intact in its tissue, suggesting the dog had not started digesting its food before it died.

“From the morphological analysis, it seems clear that they were just buried alive. They died in an instant, and thus it can be preserved,” he said. “I think there wasn’t enough time for the digestive system to actually penetrate the tissues.”

The wolf cub’s sister was later found in 2015, and showed no signs of being attacked or injured. A study published last year stated that they died when an underground cave collapsed due to a landslide. That study showed that wolves are able to prey on juvenile 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 shrank eastward by 35,000 years ago, the study said, but it persisted in northeastern Siberia and was thought to have gone extinct sometime after 18,400 years ago.

Fossils of the woolly rhinoceros are relatively rare in the fossil record, but few remains have been found since its presumed extinction, and none have yielded genetic information, making wolf stomach contents valuable to researchers.

Chacon-Duc said it was difficult to map the genome from woolly rhinoceros DNA samples because the presence of wolf DNA in the stomach complicated the analysis. For example, wolves and rhinos were both about the same age so they couldn’t 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 it with two other genomes, respectively, from woolly rhinoceros fossils found in Siberian permafrost dated to 18,000 years ago and 49,000 years ago.

Permafrost preserves ancient DNA particularly well, and scientists have found DNA molecules from the northern part of the planet that are two million years old.

The three genomes allowed the researchers to examine how the species’ genetic diversity, such as the level of inbreeding and the number of deleterious mutations, changed during the last ice age.

The study found no signs of genetic decline as the species neared extinction, suggesting that the woolly rhinoceros maintained a stable and relatively large population until the species went extinct.

Its extinction must have occurred relatively quickly, the researchers concluded, possibly as a result of global warming at the end of the last ice age, which ended 11,000 years ago.

“Our results show that there was a viable population of woolly rhinoceros in northeastern Siberia for 15,000 years after the first humans arrived, suggesting that the extinction was driven by climate warming rather than human hunting,” said Love Dalen, professor of evolutionary genomics at the Center for Paleogenetics.

Previously, the two wolf pups were thought to be early domesticated dogs or domesticated wolves. However, a 2025 study said there was no evidence that the two animals had come into contact with humans.

The work was “incredibly valuable” for understanding the evolutionary history of the woolly rhinoceros, said Nathan Wells, a senior lecturer in archeology at the University of York in Britain, who studied wolf pups but was not involved in researching the woolly rhinoceros specimen.

“Researchers know that this species was close to 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 the population appears stable at the genetic level,” he said by email.

“The authors present a reasonable conclusion that external factors, such as rapid environmental change, caused the extinction.”

Wells noted that plants, insects, and even wagtails have been found in wolf dog stomachs, and it would be exciting to apply ancient DNA methods to these dietary ingredients as well.

“Permafrost mummies give a fantastic view into the past. Normally only paleontologists and archaeologists can recover bones, but here we can better understand how these animals looked and lived,” he said. “Traces of their diet, microbiome and ecosystem are directly related to these mummies, so they play a special role for scientific analysis.”

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