Miracinonyx trumani Was Not an American Cheetah

Ice Age climate change and North American wildlife

The Ice Age films do capture one important truth: changing climates and advancing glaciers drove dramatic animal movements and evolutionary change, although it remains unclear whether any of this was caused by an acorn-burying saber-toothed squirrel breaking apart a continent.

Across the Pleistocene, from roughly 2.58 million years ago until 11,700 years ago – the period commonly described as the latest ‘ice age’ – North America was home to an extraordinary range of formidable animals.

Bears capable of reaching 12 feet when upright defecated in caves, woolly mammoths sounded their calls over freezing tundra steppes, and ‘American cheetahs’ pursued ‘American antelope’ across grasslands that were spreading.

However, an unusually wide-ranging DNA and isotope study has found that this speedy cat was not, in fact, a cheetah.

Instead, it was a sister species of today’s puma (Puma concolor) – and it had an unexpected diet as well.

"These cats were remarkably flexible, much like pumas are across their range today," explains Molly Cassatt-Johnstone, a palaeogenomicist at the University of California, Santa Cruz (UCSC), and the study’s lead author.

Miracinonyx trumani was not an American cheetah

The new study, published in Current Biology, explains that Miracinonyx trumani had been considered an American counterpart to the African cheetah (Acinonyx jubatus), found nowhere else.

That assumption stemmed from their comparable cursorial, or running, traits: elegant, slim bodies; notably long, athletic limbs; and "increased nasal turbinate capacities". These features gave them turbocharger-like noses – the terms share a linguistic link – that increased oxygen intake, though their teeth were smaller than those of related cats.

"It's very hard to imagine a prehistoric species we've never seen without comparing it to something we know," says Cassatt-Johnstone.

"But this approach can limit our understanding of ancient animals' complexity, unique evolutionary histories, and behaviors."

Researchers conducted a palaeogenomic study of four M. trumani fossils: one specimen from Wyoming, dating to around 23,000 years ago, and three from the Yukon in the Canadian Arctic, each more than 30,000 years old.

"It was just so cool to see that these cats behaved like totally different predators depending on where they were," says Cassatt-Johnstone.

The Yukon remains had previously been assigned to a separate species.

Yet confirming that they were M. trumani, isolated from their more southerly feline relatives by a glacial barrier, expanded the species’ recognised distribution by 20 degrees of latitude in one finding.

"This species of carnivore has this massive range, all the way from the Arctic to the Lower 48," explains palaeoecologist Matthew Wooler, director of the Alaska Stable Isotope Facility at the University of Alaska Fairbanks (UAF), where the isotope work was completed.

"They're demonstrating über-specialization at two ends of their range, while also feeding on two completely different food sources."

Northern Miracinonyx trumani ate fish

Most strikingly, isotope analysis suggests the northern population became pescatarian as an adaptation to its environment. The evidence came from nitrogen isotopes – heavier and lighter forms of nitrogen distinguished by their neutron numbers.

The results indicated that it ate fish including salmon, producing a chemical signature like that found in orcas and sea wolves.

It also seems to have adjusted its internal daily clock.

"We found loss-of-function mutations in certain genes that regulate circadian rhythms," notes Cassatt-Johnstone, "suggesting they may have adapted to the extreme light cycles of summers and winters in northern latitudes."

Questions still persist, among them how M. trumani established a fish-based role within a densely populated carnivore guild containing cave lions, scimitar-toothed cats, grey wolves and brown bears, as well as other predators.

"Miracinonyx persisted for a very long time without the signs of inbreeding we'd expect before a collapse," explains Beth Shapiro, an ecologist and evolutionary biologist at UCSC and the paper’s senior author.

As the Pleistocene continued, M. trumani eventually started to decline during the crucial period of climate change that marked the ice age’s end and saw iconic animals such as the woolly mammoth disappear.

"The decline was slow, not sudden, and that may be what left it unable to adapt when the climate shifted," Shapiro concludes.

The research appeared in Current Biology.

This article was fact-checked by Rachel Garner and edited by Rebecca Dyer. Although we take pride in our process, we are only human. If you notice an error, please tell us.