Scientists Say Pronghorn Got Their Speed Eluding American Cheetahs Across Wyoming

The pronghorn is the fastest land mammal in the Americas, capable of barreling over sagebrush prairies at 55 mph. But what are they running from? In their DNA, they may still be trying to outrun Miracinonyx—the “American cheetah.” It has been more than 10,000 years since a pronghorn had to escape this now-extinct big cat, but the long-held hypothesis is that their speed evolved directly as a result of evading its clutches. The best and most numerous fossils of Miracinonyx have been excavated from Wyoming, particularly Natural Trap Cave in the Bighorn Mountains.

Julie Meachen, a mammalian biologist at Des Moines University, said Miracinonyx is not really a cheetah. “It’s actually most closely related to the living mountain lion,” she said. “They’re sister species that are most closely related to the jaguar, and the three of them are distantly related to the cheetah in Africa.” The name “American cheetah” comes from skeletal similarities: long, slender legs, a shorter skull, and retractable claws. It wasn’t as robust as a mountain lion or its prehistoric contemporaries, the American lion and saber-toothed Smilodon. A fully grown Miracinonyx would probably be as big as today’s largest mountain lion but would outwardly resemble a cheetah.

While African cheetahs are so specialized for running that they have functionally given up using their forelimbs as prey-killing tools, Miracinonyx’s bones indicate it could use its forelimbs to subdue prey—the hunting style of most big cats. Even so, Meachen said Miracinonyx was undoubtedly a cursorial animal, adapted for running. “It was running to chase its prey, more so than a leopard or a jaguar,” she said.

Previous research from specimens recovered in Natural Trap Cave indicates prehistoric pronghorn was on the menu, but not exclusively. Meachen said the extinct cat had “a Catholic diet” of prehistoric hoofed mammals. “Our published isotope data shows it was eating pronghorn, sheep, and other ungulates,” she said.

The density of fossils in Natural Trap Cave, an 85-foot-deep pit cave regarded as one of the best Late Pleistocene sites in the world, gives more insight. The cave basically caught running animals—carnivores and herbivores—that fell into its depths, possibly while fleeing from predators or pursuing prey. Unlike the African cheetah, which runs mostly on flat savannah, Meachen said the American cheetah-like cat was adapted to many kinds of heterogeneous ecosystems, including mountainous, high desert terrain.

Around 10,000 years ago, most of North America’s large mammals went extinct. Miracinonyx may have been gone even earlier; the youngest specimens date to around 16,000 years ago. Meachen is studying the decline, noting that if Miracinonyx had a low population density to begin with, any extinction pressure—loss of habitat or prey—would have affected it greatly.

How fast was the American cheetah? Meachen said she is not aware of any reliable study that attempted to determine its speed. But from what she knows of its fossils and diet, Miracinonyx was perfectly capable of chasing down and killing Pleistocene pronghorn. Even though this specialized big cat has been out of the race for millennia, the pronghorn will never stop trying to outrun it.