Sabre-toothed 'kitten' mummy unearthed in Siberia is first of its kind

Shown here at left is the frozen Homotherium latidens specimen, the first known mummy of a sabre-toothed cat. On the right is a CT-scan of its skeleton. (courtesy Prof. Alexey V. Lopatin via CNN Newsource)

A mummified ice age cub from Siberia is the first known mummy of a sabre-toothed cat, and its discovery is generating ripples of excitement among paleontologists. The mummy’s exceptional preservation provided the first view of what sabre-toothed cats looked like. Written in its soft tissues are clues about where the cat’s muscles were bulkiest and how that may have shaped its hunting style.

Abundant fur and mummified flesh covered the partial corpse, and its face, forelimbs and torso were nearly intact, scientists reported Thursday in the journal Scientific Reports. The cub’s dark brown fur was short but very thick, measuring about 0.8 to 1.2 inches (20 to 30 millimetres) long. Its fur was also surprisingly soft, said lead study author Alexey V. Lopatin, full member of the Russian Academy of Sciences in Moscow and chief researcher and director of the academy’s Borissiak Paleontological Institute.

“It’s a fantastic feeling to see with your own eyes the life appearance of a long-extinct animal,” Lopatin told CNN in an email. “Especially when it comes to such an interesting predator as the sabre-toothed cat.” These extinct carnivores, which are distant relatives of modern big cats, are known for their long, bladelike canines, which could measure up to 8 inches (20 centimetres) long.

The mummy is the first evidence from Asia of the sabre-toothed cat species Homotherium latidens, Lopatin said, though fossilized bones were previously found at sites in the Netherlands and in the Canadian Yukon. Other types of frozen ice age mummies, such as woolly rhinos and mammoths, are known from the Siberian region of Yakutia in Russia.

But mummified cats, by comparison, “are extremely rare,” Lopatin said. Before this discovery, there were just two known cat mummies, both cubs of the cave lion Panthera spelaea from Yakutia’s Uyandina River basin.

“Now, we have added the Homotherium cub to this list,” Lopatin said. Extracting DNA from the mummy will be an important next step for understanding this species, as will more detailed examination of the mummy’s skeleton, muscles and hair, he added.

'At a loss for words’

Paleontologist Jack Tseng, who studies the anatomy of extinct mammals and was not involved in the discovery, was “at a loss for words” when he considered “the treasure trove of information that could come out of this singular discovery,” he told CNN.

“It’s rare to find bones of this lineage in the first place, let alone soft tissue associated with it,” said Tseng, an associate professor in the integrative biology department at the University of California, Berkeley. “I don’t know if other paleontologists’ minds are as blown as mine, but it’s like reality changes now that we’ve seen this.”

The cub was preserved in permafrost near the Badyarikha River in the northeast of Yakutia, and Yakutian diggers found the mummy in 2020 while prospecting for mammoth tusks under the supervision of Yakutian paleontologists, Lopatin told CNN in an email. Radiocarbon dating revealed that the cub was at least 35,000 years old and lived during the latter part of the Pleistocene epoch (about 2.6 million to 11,700 years ago).

Preservation of the cub’s forelimbs in particular was extraordinary, the study authors wrote. Its front paws even retained claws and the oval, fleshy pads on the underside of the paw that are fondly referred to as “beans” by admirers of modern cats.

Ancient cat origins

Along with the partial mummy, articulated bones of the cub’s pelvis and hind limbs were also found locked in ice. Based on comparisons with lion cub anatomy and analysis of the mummified cub’s incisor growth, scientists estimated that the cub was about 3 weeks old when it died.

However, the mummy also showed that sabre-toothed cubs differed dramatically from modern lion cubs of a similar age, Lopatin said. Its coat was darker, and its ears were smaller than those of lion cubs; it had longer forelimbs, a larger mouth opening and a more massive neck. The height of the mummy’s upper lip is more than twice that of a modern lion cub’s, probably so its lip could cover the long upper canines once they grew in, according to Lopatin.

Its paw is also more circular than that of a lion cub; in fact, its shape more closely resembles the paw of a bear, Tseng added. Bears are known for using their powerful forearms to dig through trees and undergrowth for food; the size and shape of the mummified cub’s paws and front limbs suggest that an adult Homotherium may have also relied on its forearms, perhaps using them to immobilize its kills, he said.

“The idea about sabre-toothed cats is that they had to have some sort of assistance from the rest of the body — that it’s not just a headfirst hunting technique,” Tseng said. “And the forearm has been one of the targets of research to think about. Are they buffer in their forearms compared to modern big cats of similar sizes, because they need a forearm to help stabilize their prey so that the sabre can be put to use?”

Until now, scientists have hypothesized about sabre-toothed cat anatomy by scanning fossils and digitally modeling the animals’ muscles in 3D, but that doesn’t compare to seeing one of those limbs “in the flesh,” Tseng said. “I think it makes it seem more possible that these sabre-tooths would have used their forearms.”

And it’s not just the anatomy of the Homotherium mummy that makes it so special — the discovery also provides a unique glimpse into the evolutionary history of the entire feline group, Tseng said. Prior genetic analysis of DNA from Homotherium fossils showed that the genus split from other ancient cats about 18 million years ago. Not only is the cub the sole mummified example of the Homotherium genus, “it represents a part of that cat family tree that goes back almost to the origin of the cat family,” he said.

“That adds to the mind-blowingness of this discovery.”