Rare woolly rhino mummies emerge from the permafrost

For most people, an extinct species is an abstraction, a set of bones they might have seen on display in a museum. For Gennady Boeskorov, they are things he has interacted with directly, studying their fur, their skin, their internal organs—experiencing these animals much as they existed thousands of years ago. Some of the well-preserved Pleistocene animals he has worked with include the mummified remains of woolly mammoths (Mammuthus primigenius), an extinct form of rabbit (Lepus tanaiticus), and cave lion cubs (Panthera spelaea).

His latest paper also makes it clear that woolly rhinoceroses belong on this list. Boeskorov is a senior researcher at the Diamond and Precious Metals Geology Institute, Siberian Branch of the Russian Academy of Sciences, as well as a professor at the North-Eastern Federal University in Yakutsk. This July, he and his colleagues described the relatively recent discovery of three woolly rhinoceros mummies, one of which is new to science, in a paper published in the journal Doklady Earth Sciences.

Woolly rhinos (Coelodonta antiquitatis) were stocky, long-haired, two-horned denizens that inhabited Eurasia during the Pleistocene, a period that includes the most recent glacial expansion. They coexisted with woolly mammoths, placing second on the list of largest animals in this ecosystem (behind their tusked proboscidean coevals), and shared a similar dense coat of hair to protect against the cold.

We’ve learned a great deal from their bones; we’re learning even more thanks to their mummies. Being able to directly observe their hair and skin, for example, offers more evidence regarding just how well-adapted these animals were to their harsh environment. And the preservation of soft tissue has allowed us to test a hypothesis that was based on a combination of the organization of their skeletons and depictions in cave art.

Woolly rhino fossils are abundant, but their mummies are exceedingly rare. To date, there have only been a handful of nearly complete woolly rhinos (although news of another has been recently announced). The three mummies in this paper all hail from Yakutia—also known as the Sakha Republic—in northeastern Russia, but they are vastly different in age and preservation.

A trio of finds

Sasha is the first complete baby woolly rhino ever discovered. Although missing about half of its body, it is arguably the most well-preserved of the three, maintaining its fluffy little strawberry-blonde head, a couple of legs, and much of its fluffy torso. The loss of its lower half prevents determination of its sex, but Sasha was between 12 and 18 months old when it died, based on its teeth and the sutures within its skull as seen through CT scans.

So Sasha might have still been nursing at the time of death. Wear on its frontal horn—the second horn following the one above its nose—may have been caused by “rubbing against its mother’s belly” as it nursed, scientists suggested in 2015. The mummy was found in 2014 along the banks of a river, and although the cause of death has yet to be determined, sediment in its nasal passages indicate drowning in mud.

By contrast, the newest mummy is missing much of one side of its body, including most of the intestines—the result of predation, according to the authors. The other side, however, preserves skin, some hair, and soft tissues. Nicknamed the “Abyisky rhinoceros” for its discovery in Yakutia’s Abyisky District in 2020, it is estimated to be a juvenile of about 4 to 4.5 years. This mummy was also found along the banks of a river and, just like Sasha, its sex hasn’t been determined.

Clues to its age, however, were found among the animal’s overall height, its skull bones, and the length and characteristics of its nasal horn (the horn that grows right above its nostrils). Like tree rings or the rings found in mammoth tusks, the number of transverse stripes on the outside of nasal horns indicate the animal’s age. The Abyisky mummy has little surviving hair; tufts of it appear in bits and pieces. The manner of death remains a mystery, but arthropod remnants in its hair indicate that its carcass spent time in a small body of fresh water.

Both the oldest at the time of her death and the oldest in terms of discovery, the Kolyma mummy was uncovered in 2007 in a Kolyma gold mine. The position in which her body was found—her legs pressed to her torso and her head stretched upwards—indicates she fell into and was trapped within a confined space. Like the Abyisky mummy, she is well-preserved on one side of her body, but she was not preserved whole. Her horns and legs were found nearby. Her skeletonized head—once joined to the body—was separated when she was excavated from the sediment. Her hair is preserved in tufts.

An udder and nipples are among the anatomical evidence that this is a female. The transverse stripes on her horn, along with teeth, skull, and height, confirm her age at death was approximately 20 years. Spores and pollen within her preserved stomach confirm what was deduced by previous studies of woolly rhino teeth: they enjoyed an herbivorous diet of grasses, shrubs, and numerous other plants.

Over the hump

The skin, hair, and soft tissues preserved in these mummies complement and expand on what we’ve learned over centuries of studying their bones. We know these animals were well-adapted to their cold, arid climate, but the thickness of their skin and the density of their hair offer further evidence. The team in this paper describes how woolly rhino hair changed over time, transitioning from lightly colored and relatively soft to darker, coarser hair as they aged. Arguably, however, this sample size is small, and there is some question about whether hair undergoes chemical changes as a result of being buried for thousands of years. This has been suggested to be the cause of different colors of woolly mammoth hair, for example.

What stands out the most in the new research is an anatomical feature suggested by the woolly rhino’s bone structure but never seen before: a fatty hump on the back of the juvenile Abyisky woolly rhino.

That hump, Boeskorov explained by email, “could serve as an additional reservoir of nutrients.” The team conducted chemical analysis of the hump, and they expect to publish further research about it in the future. As to why it has never been seen before, Boeskorov wonders if the hump may have only developed closer to winter, when fat storage might have been advantageous, or whether it had been a favorite meal for predators.

Adrian Lister, who was not involved in the research, is a paleobiologist at the Natural History Museum, London. He was not surprised to learn of the hump, he noted by email, as “we knew from the skeleton and other carcasses (and cave art) that there was a big shoulder hump—maybe this is the first time fat has actually been discovered there, which for sure is a great discovery if so.”

He agrees that it might have served as food storage, but also said that “such structures are generally considered to function as part of the display gestalt of the animal—the very big, heavy shoulder, together with the horns, providing a fearsome sight for a competitor or potential predator!”

Work on the Abyisky woolly rhino is not done. Yet to be studied, Boeskorov noted, is the area of the body that might contain internal organs such as the stomach, which could reveal more about the animal’s diet and environment. He describes being able to work with the Abyisky mummy and others as “very interesting,” as not everyone gets to touch something so ancient and so exquisitely preserved.

Plotnikov echoes this sentiment. He was also not involved in this research but collaborated on research about Sasha that was presented at a conference. He is a freelance paleontologist, and, like Boeskorov, has worked on a variety of Pleistocene mummies. “The feeling of touching something that lived tens of thousands of years ago is indescribable,” he explained by email. “It's mesmerizing.”

But beyond the personal experience, researchers don’t lose track of the scientific value. “Each bone or mummy discovery carries valuable information,” he said. The three mummies described in this paper have so much more to tell us, and future papers promise to reveal some discoveries that are currently in progress. For now, there are many questions yet to be answered, some of which may not be solved by either bones or mummies.

“People take woolly mammoths and rhinos to be ‘fellow travellers’ in the last Ice Age, which they often were,” Lister said, referencing how fossils of both species are often found together. “But intriguingly, there were large areas inhabited by mammoths that woolly rhinos never breached.” Among them, he said, is the Taymyr Peninsula in northeastern Russia. And, he continued, “while mammoths made it across the Bering Strait (probably on multiple occasions) into North America, woolly rhinos never did.” The mystery as to why may be extremely difficult to ascertain.

Doklady Earth Sciences, 2024.  DOI: 10.1134/S1028334X24602438