Whether touring a zoo or watching wildlife documentaries, most people picture the cheetah with elongated limbs, an aerodynamic chest, and a lithe, flexible spine built for blistering speed. In natural history museum galleries across North America, paleontologists frequently point to fossil skeletons of a large Ice Age felid: the extinct American cheetah (Miracinonyx trumani). Roaming North America during the Late Pleistocene, its skeletal frame was remarkably identical to today’s African cheetah (Acinonyx jubatus), leading generations of researchers and visitors to assume they were close evolutionary cousins.
On September 4, 2026, a genomic study published in Current Biology upended that century-old assumption. A research team from the Paleogenomics Lab at the University of California, Santa Cruz (UC Santa Cruz) successfully extracted and sequenced the nuclear genome of Miracinonyx trumani. The genomic data laid bare an unexpected evolutionary truth: this fossil cat was not a true cheetah at all, but rather a sister species to the modern puma (Puma concolor, also known as the cougar or mountain lion), North America’s surviving apex felid.
Ancient DNA Reveals the Split: Diverging from Pumas 2.6 Million Years Ago
The research team extracted fossil specimens preserved in Wyoming’s Natural Trap Cave and the Canadian Yukon. Led by first author Molly Cassatt-Johnstone and senior corresponding author Beth Shapiro, the researchers successfully recovered and sequenced ancient DNA (aDNA)—genetic material preserved across millennia in fossil bones.
Molecular clock analyses indicate that the American cheetah and modern cougars diverged approximately 2.6 million years ago, a milestone roughly coinciding with the period when early hominins first began fashioning primitive stone tools. By comparison, the divergence between Miracinonyx and true African cheetahs (Acinonyx) dates back some 4.7 million years. Phylogenetic trees constructed from the genomic data unequivocally demonstrate that Miracinonyx is far more closely related to pumas than to African cheetahs.
Historically, paleontologists observed the elongated limbs, lightweight skeleton, and expanded nasal cavities of Miracinonyx, hypothesizing that it represented an Old World cheetah lineage that crossed the Bering Land Bridge into North America. The genomic data demonstrates that these physical similarities are instead a textbook example of convergent evolution: unrelated species independently developing nearly identical anatomical adaptations under similar environmental pressures. On the wide-open grasslands and steppe of North America, the selective pressure to pursue fast-running herbivores prompted Miracinonyx to independently evolve a sprinting body plan.
Figure: Reconstruction of an American cheetah pursuing a pronghorn. Credit: Velizar Simeonovski / UC Santa Cruz
Arctic Fossils Reveal a Surprising Diet: Northern Populations Fed Heavily on Fish
The research team also examined three fossil specimens discovered in Canada’s Yukon Territory—unearthed at Bluefish Caves and Upper Quartz Creek—dating to between 23,000 and 31,000 years ago. These fossils pushed the species’ known range northward by an extraordinary 20 degrees of latitude, placing its habitat right at the edge of the Arctic Circle. A 20-degree latitudinal expansion is monumental, akin to finding that a species native to subtropical Florida once flourished along the Arctic tundra.
To decipher what these far-northern cats ate, researchers performed stable isotope analysis on bone collagen, measuring elemental ratios to reconstruct ancient food webs. The ratio of heavy nitrogen (nitrogen-15) to light nitrogen (nitrogen-14) serves as a biomarker for an animal’s trophic level: higher trophic status and greater meat consumption correlate with higher heavy nitrogen accumulation.
The isotope results delivered a major surprise: the Yukon population exhibited exceptionally elevated nitrogen-15 levels, comparable to marine apex predators such as orcas (killer whales). These chemical signatures reveal that Yukon Miracinonyx relied primarily on fish, likely gorging on massive seasonal runs of migrating salmon. In contrast, the southern population from Wyoming displayed standard terrestrial isotopic values, sustaining themselves on familiar land mammals.
Figure: Artistic reconstruction of dietary differences between the Yukon and Wyoming populations. Credit: Julius Csotonyi / UC Santa Cruz
The Pronghorn at 90 km/h: An Evolutionary ‘Ghost Predator’ Reassessed
These findings also prompt a critical reevaluation of one of paleoecology’s most famous concepts: the “ghost of predators past” hypothesis. Endemic to North America, the pronghorn (Antilocapra americana) can reach speeds approaching 90 km/h (nearly 60 mph)—outrunning cars on modern highways. Because modern North America lacks any extant predator that can rival such velocity, scientists long posited that the pronghorn evolved its blinding speed during an evolutionary arms race driven by the relentless pursuit of the American cheetah.
The new genomic and dietary evidence reframes this narrative. Northern Miracinonyx populations were specialized fish-hunters, while southern populations were genetic cougars that likely favored ambush tactics and short bursts over protracted open-chase pursuits. The findings suggest that the pronghorn’s extraordinary speed did not evolve solely in response to Miracinonyx.
Larisa DeSantis, a paleoecologist at Vanderbilt University, noted that the fossil record demonstrates astounding ecological and dietary plasticity. From snatching salmon at the edge of the Arctic Circle to ambushing prey on temperate plains, Miracinonyx occupied a far broader and more adaptable ecological niche than previously suspected.
Figure: Fossil distribution map of the American cheetah and new sampling localities. Credit: M. Cassatt-Johnstone et al. / Science News
A Millennia-Long Genetic Decline: Falling to Abrupt Climate Shifts
The reconstructed genome also preserved distinctive genetic adaptations. The researchers identified loss-of-function mutations in circadian rhythm genes, which govern internal biological clocks and sleep-wake cycles—a plausible genetic adaptation for surviving the extreme polar day and polar night conditions of the high north. Furthermore, Miracinonyx lost its functional sour taste receptor gene, marking the first time the loss of sour taste perception has been recorded in a fossil felid.
As for why Miracinonyx vanished at the close of the Pleistocene, catastrophic bottlenecks or abrupt mass mortality events have long been blamed. However, demographic modeling based on the nuclear genome paints a different picture: from the Early to the Late Pleistocene across hundreds of thousands of years, the species experienced a slow, continuous decline in genetic diversity.
The fossil genome showed no evidence of sudden population bottlenecks or severe inbreeding depression. Instead, as senior author Beth Shapiro observed, the protracted attrition of genetic diversity steadily degraded the species’ adaptive potential. When climate conditions swung violently at the end of the last Ice Age, the species lacked the evolutionary resilience required to survive.
First author Molly Cassatt-Johnstone summarized that the name “American cheetah” carried heavy ecological assumptions that simply do not hold up under scrutiny. Ancient DNA has cleared away decades of taxonomic confusion: its lithe, cheetah-like silhouette was merely a testament to the power of environmental convergence. Genetically and evolutionary, it was an integral member of the puma lineage all along.
References:
- Science News report
- UC Santa Cruz press release
- Current Biology paper
