This piece is part of a special project on deep time examining what the Western U.S. was like thousands, millions and even billions of years ago, and how that history is still visible and consequential today. Read more stories from the series.
One sunny June morning, I parked at a roadside pullout in western Wyoming and walked out into the sagebrush. Suddenly, two pronghorn fawns sprang up, almost out from under my feet, and sprinted away, zigzagging across the landscape at top speed. They were all spindly legs, their jackrabbit-sized bodies a blur. In a few seconds, they were hundreds of yards away and hidden from sight.
If they survived the summer and reached adulthood, they would become some of the fastest land animals on Earth. Adult pronghorn, a bit smaller than deer, can run seven miles in just 10 minutes, achieving short bursts of nearly 60 mph, much faster than horses or wolves. With their long thin legs and oversized hearts and lungs, they are built to cover ground in the wide-open sagebrush basins of Wyoming, my home state. Here, they have nibbled shrubs, dodged predators and flourished for tens of thousands of years.
Today, however, they must navigate rural housing and energy development, along with all the fences and highways that crosshatch their world. And habitat fragmentation isn’t the only threat they face: The West is already much warmer than the ancient environment in which they evolved, and it’s getting hotter every year.
The world where pronghorn have long lived — the world where I grew up and where I’m raising my children — is rapidly changing. Drought hits more often; winters are less snowy. Spring melt comes earlier, and streams run lower in late summer. We have fewer frost days, hotter summers, fiercer storms. The shifting temperatures and unpredictable precipitation mean that conifer forests are drying out, burning and dying, while rangelands are succumbing to invasive fire-adapted grasses. In 2024, over 1,300 square miles of Wyoming burned, more than double the acreage of other recent big fire years. Pronghorn feel these changes, too.
Take the pronghorn in northeast Wyoming’s Powder River Basin, a vast furrowed sea of grass and shrub-covered bluffs more than 100 miles across. When lightning sparked a fire at its western edge in August 2024, high winds whipped the flames into a raging inferno that blackened hundreds of square miles in a day. Once the evacuation orders were lifted, ranchers returned to find that places long woven into their lives had been scorched almost beyond recognition. As the burned area cooled, wildlife managers and landowners discovered at least 70 dead and dying pronghorn, some lying near fences and others out in the open where the fire had overtaken them. North America’s fastest land animal had been unable to outrun the flames.
When I read about those dead Wyoming pronghorn and saw photos of the charred earth stretching for miles, I thought about the future my kids will inhabit. In September 2018, I brought my first child home from the hospital under skies stained brownish orange from lingering wildfire smoke. I can’t predict what this landscape will look like decades from now, but I know it won’t be the same. My children will grow up in a world very different from the one we have lived in for generations.
This is not the first climatic shift pronghorn have faced, however. Their earliest North American ancestors appeared in the fossil record during the Miocene, some 20 million years ago, when the planet was warmer than it is today. Modern pronghorn evolved here later, during the much colder ice ages. Some 12,000 years ago, the ice ages ended and North America suddenly warmed up. When that happened, most large mammals died out. But not pronghorn; they held on and adapted to the new conditions.
I can’t predict what this landscape will look like decades from now, but I know it won’t be the same. My children will grow up in a world very different from the one we have lived in for generations.
Researchers say that climate change may lead to “state shifts,” where entire ecological systems — pine forest, say, or sagebrush steppe — are transformed into another. Will pronghorn survive a whole new set of climate-driven changes the way they did 12,000 years ago? Will we?
Perhaps the ancestors of the twin fawns that darted away from me that June day can help us answer those questions. If we can figure out how pronghorn survived, we might be able to learn how their descendents, and ours, can adapt to our unknowable future.
WHEN SPRING SNOWSTORMS sweep through southeast Wyoming, I see groups of pronghorn at the edge of town, near the airport, bedded down beyond the highway right-of-way fences and peering through the sideways-blowing snow. They’re migrating from their winter habitat toward their lusher summer fawning grounds, perhaps in the foothills of the mountains.
With their large eyes and antenna-like horns, pronghorn seem almost alien. But they are not so much from another world as from another time, remnants of the once-vast assembly of strange, now-extinct creatures that long ago roamed the icy, windswept basins of North America. I wanted to know more about the climate, plants and animals of those ancient times.
On the second floor of the University of Wyoming Geological Museum, a 10-foot-wide mural depicts the Laramie Valley during the Pleistocene, the series of ice ages that occurred between 2.58 million and 11,700 years ago. In a view looking toward the mountains from a bluff outside what is now my hometown, a muscular saber-toothed lion snarls at a massive bison whose long horns extend sideways like spears. Three mammoths with curved ivory tusks and heavy fur robes look on warily. Small scrubby plants blanket the tundra and a fringe of willows lines the Laramie River. Beyond it, glaciers reach down the drainages of the treeless Medicine Bow Mountains. Deep ice and snow cloak the mountain range, with familiar rocky peaks jutting into the sky above.
I found paleoclimatologist Bryan Shuman in a nearby university building, where he was settling into a new office. Boxes of books and papers surrounded his desk, their sedimentary layers containing stories of the past. A professor in the UW Geology and Geophysics Department, Shuman examines microscopic particles in lakebed sediment cores and diagrams ancient lake shores, piecing together the hydrology, climates and ecologies of environments as far back as the late Pleistocene.
Laramie is known for its cold temperatures, but Pleistocene Laramie was even colder. Shuman’s research shows that here in the Central Rockies, where more than a third of the world’s pronghorn live today, year-round average temperatures during the coldest periods of the Pleistocene were as low as 18 degrees Fahrenheit colder than now — cold enough for the ground to freeze into wedges of permafrost that left polygon-shaped patterns on the ground, still visible outside of town.
The mural’s depiction of ice and plant cover rings true. “We know glaciers were much more extensive,” Shuman said. “There’s very clear geomorphic evidence where the glaciers were.” Not many trees lived in that frosty environment. Shuman showed me a graph plotting the temperature over thousands of years next to pollen meticulously extracted from lakebed mud layers. “You can see when it was really cold, it was mostly a grass- and sagebrush-dominated landscape,” he said. Researchers have also found pollen from willows, perhaps similar to the low, shrubby willows that blanket the Arctic today.
Will pronghorn survive a whole new set of climate-driven changes the way they did 12,000 years ago? Will we?
The landscape was drier than it is today, too. Shuman uses ground-penetrating radar to map past lake shorelines as a clue to how wet the landscape was. “We are living in an unusually wet time. …This is probably the wettest time in the last 20,000 years, at least,” for our region, he said.
The late Pleistocene here was also windy and “really dusty,” according to Shuman. Glaciers pulverized rocks into silt that washed out with meltwater, dried and blew away. The Pleistocene wind eroded hollows in Wyoming, shaped dunes in the Great Plains, and deposited thick layers of glacial dust for hundreds of miles throughout the Midwest.
I tried to picture pronghorn, like those huddled against modern-day spring snowstorms, moving through an ancient landscape even colder, drier, windier and dustier than today’s.
PLEISTOCENE PROGHORN had more to worry about than the weather. Fossils show that even in that harsh environment, several of the big, strange predators that thrived in Wyoming hunted them —Miracinonyx, for example, the American cheetah, a 160-pound relative of the mountain lion with long legs ideal for running down and grappling with its prey. There was also the vicious American lion, at up to 1,000 pounds one of the largest cats ever to roam the Earth, and the powerful Beringian wolf with its heavy jaws and big teeth. Paleontologists examined isotopes in their fossils and found evidence that all three
ate pronghorn.
Their bones were preserved in Natural Trap Cave, a vertical, bell-shaped cavern on the western flank of the Bighorn Mountains in northern Wyoming, whose opening is an oval hole about 15 feet across. Over the last 47,000 years, animals have stumbled into the hole and fallen more than 80 feet into the cave, where they either died of their injuries or starved. Since no scavengers could reach the carcasses, complete skeletons remain inside Natural Trap Cave, disturbed only by rising water or falling rocks. The cave’s steady 42-degree Fahrenheit temperature preserves both DNA and bones.
Julie Meachen, a vertebrate paleontologist from Des Moines University in Iowa, has led a Natural Trap Cave research team since 2014. At the start of her first field season, she bumped up a rough four-wheel-drive road to the cave, where an experienced caver set up a rope system. “I was a little intimidated by rappelling in 80 feet,” she told me. “I had never done anything like that before.”
As Meachen lowered herself slowly into the cavern’s mouth, she saw bones poking out of the walls. Researchers in the 1970s and ’80s had found the remains of camels, cheetahs, horses and even mammoths in the cave, but no one had been inside it for decades. “We just knew that it was a treasure trove of fossils,” she said.
Alongside the bones of Pleistocene lions, wolves and bears, paleontologists in the 1970s and ’80s found pronghorn remains that were between 17,000 and 20,000 years old and indistinguishable from those of their modern descendants — along with evidence of at least 14 other large mammal species. There were modern bighorn sheep and coyotes, extinct Pleistocene herbivores that resembled stilt-legged horses, musk oxen and camels — even giant short-faced bears more than twice the size of modern grizzlies.
This past summer, Meachen’s crew dug up a scapula, ribs and several vertebrae from a mammoth, whose skull may still be hidden under the dirt. The bones belong to one of at least three mammoths that fell into the cave during the Pleistocene, said Meachen.
Todd Surovell, an archaeologist at the University of Wyoming who studies hunter-gatherers, has worked on mammoth dig sites in Wyoming and written about late-Pleistocene extinctions. When I stopped by his campus office, he passed me a small Ziploc bag holding a walnut-sized piece of bone, smooth creamy white with jagged brown ripples on one side. sh
“Mammoth ivory,” he said. This particular tusk shard was from Alaska, he added, but “Columbian mammoths, there’s a lot of them in Wyoming.” Columbian mammoths — the biggest species of mammoth in the Americas — ranged from Canada to Mexico along the front of the Rockies.“Just tons of mammoths,” Surovell said.
I picture one of those 22,000-pound giants twisting its trunk around a tussock, stuffing grass into its mouth, its 16-foot-long tusks sweeping through the air while pronghorn tiptoed past, trying to evade lurking lions and bears. Such scenes played out for tens of thousands of years — until something drove most of those animals to extinction.
“We are living in an unusually wet time. …This is probably the wettest time in the last 20,000 years, at least.”
ON A GEOLOGIC TIMESCALE, the 7,000-year transition from the deep ice age to the Holocene, the epoch we’re still in today, happened in an instant. But for pronghorn, the changes unfolded over many hundreds of lifetimes.
Around 17,000 years ago, the Earth’s axis, which slowly wobbles on a 41,000-year cycle, was moving toward maximum tilt, letting in more summer solar radiation. The ice caps started melting, and as the white, reflective ice retreated poleward, the darker ground surface absorbed more heat from the sun. Shuman, the paleoclimatologist, pointed me to a textbook, Earth’s Climate: Past and Future, which I pored over for days, trying to wrap my head around the end-Pleistocene warming and how scientists have studied it.
I learned that as the ice caps melted, an enormous amount of fresh water poured into the oceans, taking sediment and dust with it and eventually raising the sea level some 360 feet. All that water shifted currents and warmed the oceans, causing them to release carbon dioxide. Rising atmospheric carbon dioxide created a greenhouse effect, trapping heat from the sun and causing further warming.
“This chain of orbital changes, ice sheet changes, dust and ocean changes, all causes carbon dioxide to go up and down,” Shuman said. Carbon dioxide, he added, “is probably the biggest single hammer on the system.”
By about 10,000 years ago, atmospheric carbon dioxide had risen more than 40%, warming the planet by 7 to 11 degrees Fahrenheit. The center of North America got wetter. Grasslands became less dusty and arid; forests marched northward. Pine, spruce and fir flourished, according to pollen records. But what was good for trees was not necessarily good for megafauna. “A lot of the big things that used to be here just didn’t survive,” Meachen said.
Of the many dozens of large mammals that roamed Pleistocene North America, at least 59 — and possibly far more — went extinct. (Only 26 are still around today.) By one analysis, 72% of large mammal species disappeared from the continent, everything from horses and mammoths to giant beavers and ground sloths, as well as many predators.
“The bigger you are, the more likely you are to go extinct,” Surovell said. “Very few small things go extinct.” One analysis that he co-authored in 2009 found that it’s likely all those animals died out between 13,800 and 11,400 years ago — a mere flash in the geologic time frame. I asked him what’s changed since that paper came out. “It’s only gotten stronger, the evidence.”
Why so many large land mammals died out all at once is a great mystery, long debated and still unresolved. Scholars continue to investigate potential causes, ranging from the influence of humans to a possible asteroid impact or a disease that jumped between species. But scientists generally agree that abrupt climate change played a major role in driving down biodiversity.
AMONG THE SURVIVORS, one of the animals that has been here the longest is the pronghorn antelope. Antilocaprids have been on the continent more than four times longer than the cervids; the ancestors of deer, elk, moose and caribou entered North America around 4.8 million years ago. Ancestors of modern bovids — bison, bighorn sheep, mountain goats — showed up a mere 2.5 million years ago. But modern pronghorn, the only living descendant of the first Antilocaprids, are unique to North America, having evolved to thrive right here.
“In fact, they were survivors,” said Christine Janis, professor emerita of ecology and evolutionary biology at Brown University. She studies animal evolution related to climate change over the past 20 million years and has authored many influential texts on fossil Antilocaprids and other hoofed mammals. The pronghorn’s ancestors made it through earlier extinctions of ancient deer-like animals around 5 million years ago, she told me. “They survived along with things like horses and camels until all these guys went extinct at the end of the Pleistocene.”
“Be small and be adaptable in your diet. That’s a good way to survive.”
No one knows exactly how they did it, but everyone I asked had a theory. Meachen cited their ability to live with little water. “They were able to eat dry, scrubby vegetation that other big herbivores, like horses and bison, were not able to eat and make use of, and they were able to do that and have less water stress than other animals,” she said.
“You know,” Surovell added, “another thing that they probably benefited from was the extinction of the American cheetah.”
Janis credited pronghorn’s high-crowned teeth with enabling them to live on low-growing, gritty browse. Teeth that extend well above the gumline have plenty of room to slowly wear down, even if the animal spends its life chewing dusty Pleistocene plants. She also noted their small size, which allows them to reproduce faster than bigger animals. Whereas a huge camel or mammoth might have just one calf every few years, pronghorn typically have two fawns each spring. She put the survival lesson from pronghorn succinctly: “Be small and be adaptable in your diet. That’s a good way to survive.”
PRONGHORN HAVE SURVIVED many changes so far, and there’s more to come. Each year, it seems, Earth’s surface temperatures set new records for the hottest since record-keeping began. The greenhouse gases we are adding to the atmosphere today are expected, over the next 75 years, to drive a shift in global average temperatures far more rapid than the one that, over a span of 7,000 years, ended the ice ages, shrank the ice sheets, melted the permafrost and glaciers and transformed tundra into forests, in the process wiping out so many large mammals. “That’s the type of magnitude change we’re talking about,” Shuman said, “except it’s going to keep going into a warmer direction that’s still hard to imagine.”
The future feels precarious, both for pronghorn and for us. Planetary changes are happening at a speed likely not seen since an asteroid killed the dinosaurs some 66 million years ago. Can we adapt our own living systems to such rapid and massive changes?
As an inhabitant of this place and the mother of two other Wyomingites, I can barely stand to consider that question. Still, studying how pronghorn survived has shifted my perspective in some ways. I’m glad I didn’t live in the arid, treeless, bitter cold of the deepest ice ages. I know that in places, increased precipitation has helped forests and even some animals, including pronghorn, thrive in these warmer modern times. I know that the Earth has sustained life for billions of years through many climates, from periods warm enough to support palm trees and crocodiles in Wyoming to millennia locked in snow and ice and back again. Part of the wonder of our planet is its dynamism and the way living systems continuously adjust. I know that, more easily than most animals, my children can alter their diets and, like pronghorn, survive in a range of climates and environments, even moving to new habitats if they must.
When that rangeland wildfire torched nearly 275 square miles in Wyoming’s Powder River Basin in 2024, the 70 pronghorn that died left tens of thousands of survivors in the area. Those survivors birthed new fawns and fed on the green grass that sprouted in the burned areas the following spring.
Perhaps the lesson from pronghorn is not to yearn for the past or worry over the unknown future, but to face the day with attention and quiet care, noticing shifts in the wind and scents in the air. Pronghorn tell us to know our home habitats deeply and to shape our own patterns and behavior to align with the forces of the land. They tell me to read changes in how the snow drifts, notice which plants emerge after a soaking thunderstorm and realize that each spring will be different from the previous. They tell me to teach my children to recognize birdsong, learn how animals come and go with the seasons, breathe deeply, and keep moving forward with my feet on the Earth.
This story is part of High Country News’ Conservation Beyond Boundaries project, which is supported by the BAND Foundation.
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This article appeared in the January 2026 print edition of the magazine with the headline “Lessons from an ice age survivor.”
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