When The West Was Seriously Wild
The big cat presses its belly to the frozen ground and crawls forward, inch by silent inch through the low sage. The midmorning sun rising at his back offers little warmth, but the cat has learned from hard won experience that low-angle light glinting off the glacier makes it difficult for his prey to see. He uses this, and the wind in his face, to painstakingly close the gap between himself and six pronghorn antelope grazing in the shallow valley bottom. At 60 yards he coils stone-still, watches and waits. His eyes are riveted to the wary ungulates, taking in all of them and none of them with a steady-eyed stare, scanning not for sickness or weakness, but the telltale movements of the unlucky.
A buck at the edge of the band quarters away and drops his head to feed. The cat is off like a shot. The time for stealth has passed. It’s a footrace now, winner take all. The buck wheels and digs for the opposite ridge. The cat anticipates each maneuver and uses its long heavy tail to pivot and cut accordingly. They crest the ridge nearly side by side. The slender cat is taller at the shoulder than his prey making the final bound to its back an effortless, if precisely orchestrated act. Success seems close at hand as retractable claws sink deep into the pronghorn’s neck. But then, just as he fastens his short muzzle to the buck’s throat, the ground falls away beneath them and they cartwheel headlong into darkness. Eighty-five feet below they meet their death together, atop a pile of bones
Fifteen thousand years later a new hunt begins, this one taken up by human scientists. It is a hunt for answers and for understanding. What exactly was Miracinonyx Trumani, the prehistoric cheetah-like cat that roamed Wyoming and much of ice age North America? How did it live? What role did it play in the evolution of Wyoming’s modern day wildlife?
Natural Trap Cave, a bell-shaped vertical pit in the Northeastern foothills of the Bighorn Mountains is a natural place for that hunt to begin. Innumerable animals, including multiple cats, fell in over the course of millennia, building layer upon layer of well-preserved fossils, and establishing a treasure trove of clues.
Dr. Julie Meachen, Paleontologist, Assistant Professor of Anatomy at Des Moines University, and co-leader of the latest round of investigation at Natural Trap Cave starts her pursuit of the answers down in the hole, by exhuming and examining the physical evidence. The fossil record she and her colleagues have uncovered provides some definitive information about the cat’s build and biology. DNA analysis tells them that it was a sister species of both the modern mountain lion and African cheetah, though not an ancestor of either. Bones and bone fragments show that it was taller and heavier than either modern cat, perhaps better than three feet at the shoulder and nine feet from nose to tail. It had a slender frame, long limbs, and a rounder, shorter skull relative to a cougar.
The shape of an animal only tells us so much though. To paint a more complete picture scientists consider the creature’s circumstances.
Perhaps no circumstance is more telling than the environment in which it lived. “The Big Horn Basin was a much colder, drier place in the late Pleistocene,” says Dr. Bryan Shuman, University of Wyoming Associate Professor of Paleohydrology, Paleoclimatology and Paleoecology. The vast continental ice sheets that gave the “ice age” its popular name didn’t extend to Wyoming, but “The Big Horns, Winds, Absarokas and other ranges were extensively glaciated.” Lakes in the region were considerably lower. Sediment records taken from those lakes reveal that plant communities were different too. “We find almost no evidence of tree material from back then.” That fact, and other bits of evidence, suggests an open landscape, dominated by short sages and other low species. “I imagine something like the high deserts of Eastern Oregon, crossed with an Alaskan tundra,” says Dr. Shuman. This stunted plantscape may have been due in large part to the make-up of the air. “Carbon levels in the atmosphere were so low that plants would have had a hard time thriving.“
Slow growing vegetation did not translate into a lack of animal life. A startling array of critters – the diversity and sheer biomass of which far outstrip today’s – lived and died in that sparse country. Mammoths, camels, horses, elk, bison, bighorn sheep, mule deer and multiple species of pronghorn roamed the land with untold other species. And as always, where there is meat, there were carnivores. The cheetah shared the stage with 500 pound North American lions, 11 foot tall short faced bears, sabre toothed cats and dire wolves, along with the cougar, gray wolf, coyote, wolverine and bear species that we know today. Late Pleistocene Wyoming was not a hunting ground for the faint of heart.
That crowded field may hint at behavior. “Most felids are opportunistic,” says Wyoming Game and Fish Department Large Carnivore Section Supervisor, Dr. Dan Thompson. “They can generalize if conditions are right. But scarcity, competition or other limiting factors can promote specialization among a certain population or even individuals.” In other words, left to its own devices, a big cat like Miracinonyx would gladly sample its way through the buffet of life. But when faced with tough conditions, or crowded by other predators, they likely stuck to what they did best.
“I think there was a lot of niche specialization in the Pleistocene,” agrees Dr. Meachen “We just don’t know what all of the specializations were.” But with years of functional morphology experience – the science of using body form to determine how an animal made a living e.g. what it ate and how it moved around – she can make some educated guesses. Long limbs suggest high-speed pursuits over significant distance. Enlarged nasal passages in a short round skull are ideal for for the high volume oxygen intake needed by long distance sprinters. A long, heavy tail enhances balance and agility. That Miracinonyx specimens are primarily found in open country sites further strengthens a cheetah style stalk and chase hypothesis.
It can’t be ignored that the characteristics of another creature have helped shape that line of thinking as well. Experts have long puzzled over the pronghorn antelope’s blistering speed. Nothing in modern North America comes close to matching its pace. Why, they struggle to understand, would such a trait have evolved without an ultrafast predator driving the natural selection? Could Miracinonyx account for the pronghorn’s need for speed?
It’s an appealing “just so story” for experts and amateurs alike. The only problem is that there’s no hard evidence forging the link. At least not yet. Researchers hope to one-day fill in some of the blanks with a space age technique called stable isotope analysis. By analyzing the types of carbon in the cat’s tooth enamel, they may be able to determine what types of plants its primary prey fed on. That information, in turn, would narrow the list of the cat’s likely food sources and more firmly fix the cat in position on the food chain.
Carbon isotope ratios that resemble a diet of pronghorn would make for a nice clean explanation. But what if it turns out Miracinonyx favored big horn sheep? Long limbs, round heads and rudder-like tails are also useful in the mountains, points out John-Paul Hodnett of St. Joseph’s University Biological Sciences Department. One need look no further than the Himalayan snow leopard to see that. And Miracinonyx does turn-up in the fossil record of the Grand Canyon. Could the ancient cheetah-like cat have actually been more of an uplands hunter?
For now we’re left with more questions than answers. A long, tall, slender cat lived amid a mixed cast of storybook creatures and modern species, not altogether that long ago. That much we can say with certainty. Until scientists provide more puzzle pieces, we’ll have to settle for following Miracinonyx Trumani over the hills and through the canyons of our imaginations.
* An edited version of this story originally appeared in the January 2015 issue of Wyoming Wildlife magazine under the title On The Run.