With their slender bodies and long front legs, Miracinonyx trumani—often nicknamed the "American cheetah"—was long thought to be a North American analog of the African big cat. But in a new study publishing September 4 in the Cell Press journal Current Biology, researchers reveal that the extinct cat was more closely related to pumas. Some populations living near the Arctic preyed almost exclusively on fish, challenging the long-held assumption that these "cheetahs" chased fast-running prey, such as pronghorns.
"It's very hard to imagine a prehistoric species we've never seen without comparing it to something we know," says Molly Cassatt-Johnstone, the paper's first author from the University of California, Santa Cruz. "But this approach can limit our understanding of ancient animals' complexity, unique evolutionary histories, and behaviors."
The American cheetah roamed North America's open grasslands during the Pleistocene epoch, about 2.5 million to 16,000 years ago. Based on fossils uncovered to date, M. trumani had a slender body shape, long forelimbs, and large nasal cavities—features that are characteristic of modern fast-running animals such as cheetahs or horses. In addition, paleontologists have discovered some M. trumani remains alongside those of pronghorns, fast-running animals known colloquially as the "American antelope," leading researchers to assume that the extinct cat had a similar lifestyle to modern African cheetahs.
However, in recent years, increasing evidence has suggested that M. trumani may not have been as cheetah-like as its appearance suggests. To delve deeper, Cassatt-Johnstone and her team sequenced the most complete M. trumani ancient DNA set to date from four specimens, one from Wyoming and three from Canada's Yukon territory. The Yukon samples were previously thought to be a different species, but the team confirmed that they belong to M. trumani, extending the known range of M. trumani more than 20 degrees of latitude farther north than previously known.
The researchers then compared M. trumani's DNA with that of nine other cat species, ranging from lions to house cats. They found that M. trumani shared a common ancestor with modern cheetahs about 4.7 million years ago. The species was most closely related to modern pumas, having diverged from a common ancestor about 2.6 million years ago.
Curious about what M. trumani ate in the absence of pronghorn, which aren't found as far north as Canada's Yukon territory, the team analyzed the nitrogen and carbon in the Yukon fossils to determine their diet and where they sat in the food chain.
The team found that despite being discovered in different locations and having lived hundreds of years apart, the Yukon M. trumani individuals all showed signals indicating that they preyed almost exclusively on fish. The fossils' nitrogen profiles were similar to those observed in fish-specialist orcas and sea wolves living along the coast of British Columbia, which eat mainly marine animals. In contrast, the M. trumani in Wyoming had the nitrogen markers of a terrestrial predator that mostly eats herbivores, similar to lions.
The drastic range of M. trumani's diet suggests that the animals were able to adapt to a variety of food sources. Such flexibility may have helped the species survive across diverse environments, from the subtropics to the Arctic, Cassatt-Johnstone says.
The researchers also found that two of M. trumani's genes involved in circadian rhythm regulation were nonfunctional. These genes help control animals' internal clocks, which use cues like sunlight to determine when to sleep. In M. trumani, the loss of these functional genes may suggest that populations living at high latitudes adapted to extreme periods of daylight and darkness, or that the animals were nocturnal.
"It's really surprising and exciting to identify another predator present in Beringia," Cassatt-Johnstone says, referring to the ancient land region connecting northeastern Asia and northwestern North America during the Pleistocene, where woolly mammoths and other large mammals roamed.
Like the woolly mammoth, M. trumani likely went extinct as the last ice age transitioned to the warmer Holocene.
"There are probably other extinct species that, unfortunately, have been reduced to fewer dimensions than they deserve," Cassatt-Johnstone says. "The M. trumani fossils suggest that this 'American cheetah' was far more adaptable than its nickname implies."
