A similarly crucial transformation happened around the same time in the horse’s digestive tract. Most herbivores are ruminants that ferment plant matter in their stomachs. Horses developed a specialized fermentation chamber near the end of their digestive tract, called the cecum. Elephants and rhinoceroses also have a cecum, or “hindgut,” which is located between the intestine and the colon.
Hindgut digestion is less efficient than the digestion of most other herbivores, including cows and deer. A horse can extract only 45 percent of nutrients, while a ruminant can extract 60 percent. But a hindgut also gives horses a big advantage: They can eat low-quality food that ruminants can’t. Ruminants must selectively graze tender grasses to maintain the slow process of bacterial breakdown in their stomachs. Hindgut herbivores don’t have the same limitation. They can eat harsh grasses and shrubs a cow wouldn’t touch. Forage passes through a hindgut system relatively quickly, so even though horses get less energy from every bite, they can take a lot more bites, so they end up getting more nutrients. This allows them to survive on forage that is too rough for most other animals.
I remember being out in a wind-whipped stretch of Nevada desert with a rancher who was explaining to me how he had to take his cattle out of a pasture because wild horses had eaten all the grass. If the grass was largely gone, I asked, how were the horses still surviving? “Shoot,” he said, “wild horses can get fat in a place where a cow would starve.”
About twelve million years ago, a volcano erupted in Idaho and began spewing thick plumes of ash that the wind carried eastward almost a thousand miles, where the ash rained down over what is now eastern Nebraska. By the time it was all over, the fine, silvery ash was a foot deep across the state and ten feet thick where it drifted. As the ash sifted down, large mammals—choking on the dust—made for the nearby water hole, where hundreds collapsed of lung failure and were covered over with more dust.
The ash became rock, preserving that moment in time. Then, starting in the 1970s, it was excavated by paleontologists. You can now visit the stunning jumble of stricken skeletons at Ashfall Fossil Beds State Park: camels, giant tortoises, pint-size North American rhinoceroses, and five species of horses that ranged from a gazellelike three-toed horse called Protohippus (first horse), to a medium-size three-toed group called Hipparion (ponylike horse), to the ancestor of the modern horse, called Pliohippus (horse from the Pliocene Epoch), which stood on one central hoof, its other toes little more than calluses on its ankles.
The epoch when the volcano blew, known as the Miocene, lasted from about twenty-three to five million years ago. It was the boom time for horses. North America boasted at least nineteen species. Like the ungulates of today’s African savanna, they fanned into different niches. Some were forest dwellers, some ate grass. Some were almost as big as modern horses, others were small and light like antelope.
One of the most widespread species was Dinohippus (terrible horse). It was larger than previous horses, though still pony-size by today’s standards—about fifty inches at the shoulder. More important than size, though, were its innovations. Dinohippus lived on the open grasslands where predators like dire wolves and saber-toothed cats prowled. Dinohippus evolved under the twin pressures of a grass diet and lurking meat eaters. Its mouth became packed with broad, long molars and it had a strong, thick jaw for grinding grass. Its face grew longer, with eyes set farther up on the head so that it could graze while still keeping watch above the grass for predators. These changes to the head made Dinohippus look very much like a modern horse.
The leg bones that allow many other mammals, including humans, to rotate their ankles, changed, too. They became fused to allow only forward and backward motions. This made horses stronger and more efficient. Dinohippus could stand with leg bones locked in place while grazing to conserve energy, and could run with increased speed.
In terms of evolutionary success, this new design was a hit. During the Miocene, the horse family, in all its variations, spread from North America to the rest of the world. They covered Florida, Oklahoma, and Texas in great herds. They crossed the Bering land bridge—which then was not a narrow bridge, but a plain hundreds of miles wide—and spread all the way to the ends of Europe and the cape in Africa.
“You just find them everywhere,” said Rose. “There are places where there are just piles of them in Asia.”
Spend any time looking at the history of life in the last fifty million years and what becomes astounding is not only the innovations but the constant beat of catastrophe: volcanic explosions that blotted out the sun, meteor impacts that hit like a nuclear Armageddon, repeated ice ages. Continental collision. Climatic upheaval. Droughts and storms that likely eclipse what we have ever witnessed. And yet horses thrived.
This is significant because an awful lot of other life didn’t. Giant sloths, gone. Car-size armadillos, gone. Mammoths and mastodons and any number of other strange pachyderms, all gone. The Hyaenodons and Gastornis that preyed on horses, gone. Taking the long view, the story of life on Earth is mostly a story of death. Only one out of every thousand species that ever existed is still alive today. Bad things happen all the time. Five million years ago, North and South America reconnected for the first time since dinosaurs roamed the earth. Eight-foot-tall flightless birds called Phorusrhacidae, known informally as “terror birds,” invaded North American savannas. For two million years, they stalked small horses, hunting with axelike beaks and top speeds estimated at over fifty miles an hour. No doubt they ate their share of horsemeat. But horses are still here, and terror birds are not.
A threat even more fearsome than terror birds popped up around the same time that the two Americas joined. It was a new kind of grass. As the steamy jungles of the Eocene slowly ceded to open savannas, the grass that took over was almost all of one type called C3 grass, named for the type of photosynthesis it used. Starting about seven million years ago, a type of grass known as C4 started to spread. C4 had a more efficient recipe for photosynthesis, so it could grow faster, especially in hot, dry areas where growing seasons were short. But it had another advantage. C4 grasses could store five times as much abrasive silica as C3. It was a built-in defense mechanism because it was too gritty for most animals to chew. But not horses. As the abundance of C4 grasses increased, so did the length of the horses’ teeth. Paleontologists have found that horses were some of the first large herbivores to be able to stomach this new food. Herbivores that couldn’t adapt either died out or evolved to find sources of C3 grasses and shrubs.
It was with this last environmental change that many of the horse ancestors disappeared and the modern horse genus, Equus, emerged in North America, somewhere between three and six million years ago. What did Equus look like? A number of modern examples are still around us: zebras, wild asses in Africa, and a donkeylike resident of the Mongolian steppes called the onager. As for the true wild horse before it was domesticated, forget the image of the lithe Thoroughbred. The best indication we have of their shape and size is from paintings in the caves of southern France. Here, between thirty and fifteen thousand years ago, Paleolithic hunters recorded the shapes and colors of the animals they saw. They were stocky with big heads, short legs, and big, barrel-shaped bodies. They had short manes like those on zebras. They were mostly dun-colored, though some had stripes at the base of the neck and some had spots. For a long time, most paleontologists thought the paintings on the cave walls were just doodles that didn’t show what ancient horses looked like, but a 2011 study examining ancient horse DNA found that the paintings were probably right. Ancient horses, like horses today, varied in color.3
Some wild horses today still have remnants of stripes on their legs and necks.
At the end of our day collecting fossils in Bighorn Basin, Professor Rose had found dozens of jaws, and I had managed to spot three. Our finds were all small enough to fit in Rose’s pocket. “That’s the nice thing about Eocene mammal bones,” he said as we walked back to the Suburban. “Not much to ca
rry.”
Back at camp, I washed off the dust and sweat in a small, plastic tub. After dinner, we gathered at the table in an old RV that Rose uses as his field laboratory, and the students dumped out what Rose called their “goodies”—the day’s haul of fossils.
“A lot of what we find doesn’t have much significance on its own,” Rose said. “It’s only when we get it back in the lab and really compare it with everything else we’ve collected that we can see how things started to change.”
I was so spent from a day in the dry heat that I couldn’t bear thinking of the team going out day after day, but the slow shuffle in search of the past had left an impression on me. The transformations and tribulations the horse went through, from the jaw I had held in my hand to the wild mustangs we saw on the horizon, were so revolutionary that the change from wild to domestic and then back again seemed minor.
After what I had learned, I felt that the horse deserved to be counted as a native in North America. It had developed here and lived here for more than about fifty-five million years. It had disappeared ten thousand years ago, but then it had returned to its home range when Europeans arrived. Since then, it has thrived, sometimes despite our best efforts.
If the fifty-five-million-year history of horses in North America were condensed into a day, horses would be a native species right up until they became regionally extinct at 11:59:43 p.m. When they returned in the last second of the day, why did they no longer belong?
There was one more part of the story I wanted to understand: the disappearance. Why, after fifty-five million years, had the horse gone AWOL, and what effect did that have on any claims to being a native species?
To try to answer that, I headed to the University of Colorado in Boulder, where a drawer in the offices of anthropologist Douglas Bamforth held some promising evidence.
The office, in a castlelike, 130-year-old stone science building that is one of the oldest on campus, had grand oak specimen drawers and tall windows to let in natural light. In that setting, I half expected Bamforth to arrive with a herringbone jacket and a pipe clenched in his teeth. But Boulder has become a casual place, and he arrived in jeans and a Patagonia pullover, having just come from the gym.
As the local anthropologist, he told me, he gets a lot of calls from the public. “Pretty regularly anyone who finds a triangular rock will come in and ask if it’s an arrowhead,” he said with a long-suffering sigh.
One of those calls came in on an afternoon in 2008 from a doctor who was having a koi pond built in his backyard at the edge of town. “I went up there to check it out, a bit reluctantly,” Bamforth said. “And what I found was really astonishing.”
Workers digging a shallow pit had found more than eighty stone tools—scrapers, cutters, and spear points that dated to about thirteen thousand years ago. Some of them were nearly the size of a dinner plate and exquisitely crafted to almond-shaped points with delicate serrated edges made by carefully flaking both sides with precise hits from a stone. These were not just arrowheads—they were rare Clovis points dating back to the period when the first humans arrived in North America. This was also the time when the horses disappeared.
The name Clovis comes from an archaeological site near Clovis, New Mexico, where the first points from the era were found amid mammoth bones in 1929. Since then, Clovis sites have been uncovered in all corners of the Americas, and they are almost always associated with the hunting of huge mammals. Though much about the Clovis people is still unknown, the leading theory is that they came across the land bridge from Asia about fifteen thousand years ago, just as the glaciers from the last ice age were retreating. Everywhere they went, they left large, exquisitely crafted, stone spear points. Within a thousand years, these small bands of hunters had reached the tip of South America, a spread that one anthropologist described as “an unprecedented rate of diffusion not seen again until the invention of the hula-hoop.”4
All evidence suggests Clovis hunters were an even more disastrous introduction for North American fauna than the South American terror birds had been. Within a few thousand years of their arrival, more than thirty large animal species had disappeared from North America, an event known as the Quaternary Extinction. Mammoths, giant sloths, giant beavers, saber-toothed cats—all disappeared. There has been a great deal of debate among scientists as to whether the extinction was caused by hunters, climate change, or both. There is still no consensus, but most think Clovis played a big role.
Professor Bamforth picked up the biggest, most striking stone tool from the drawer, a broad, almond-shaped point so big it filled both of his hands.
It was made of a honey-colored stone with the soft shine of hard toffee, and expertly flaked edges still looked sharp, more than 10,000 years later.
“This stone isn’t from around here,” he said. “None of this stone is. It comes from hundreds of miles away. What that shows us is that these hunters were highly mobile, highly skilled, and knew the land well.”
In 2009, with the permission of the doctor who uncovered the points, Bamforth sent the stone tools to a lab in California to see if any residue containing DNA could be recovered. It was a long shot—the tools had been buried for hundreds of generations—but it was worth a try.
The results came back positive. Three of the tools had ancient DNA. One was of camel, one was of sheep, and one was of horse. Horse DNA has been found at numerous other Clovis sites since then. Horse bones have been found piled next to Clovis hearths. There is no evidence Clovis people dined on horses alone, but evidence does suggest they dined on horses a lot.
So, does that change whether the horse is a native species? If we classify nonnatives as species introduced through the interference of man, how do we adjust when a species may have been wiped out by man? In modern times, we have reintroduced countless species that have been regionally wiped out by men—elk, bighorn sheep, buffalo, mountain goats, condors, falcons. Does it matter if their absence is measured in millennia instead of decades?
Maybe it does matter. If an animal has been gone so long that the rest of the ecosystem has moved on, and left no room, then perhaps the case can be made that a species is no longer a native. I asked Bamforth about this. Are the grasslands of the West much different today than they were ten thousand years ago? “It was cooler then, and drier,” he said. “But no, the species are basically the same.”
Evolution can have a long memory. The North American pronghorn evolved to outrun a North American cheetahlike cat that was wiped out when Clovis points showed up. The pronghorn can still run at sixty miles per hour, even though it hasn’t needed to for millennia. Maybe the horse and the western grass are the same way: After developing together for so long, they still remember in their DNA what it was like to live together.
The Bureau of Land Management, many ranchers, and even some conservationists argue that because the wild horse was introduced, it does not fit in the ecosystem here. It is therefore a damaging invasive and must be tightly controlled. That is in part why roundups have continued for decades. That is why we have fifty thousand horses in storage.
Any argument against counting the horse as native is biologically naive. Spend time with paleontologists and you learn to take a longer view. They don’t use the word native. Nor do they talk about a delicate balance in the ecosystem. All they see is upheaval and change. Nothing lasts. From this point of view, it’s hard to give a concept like being “native” much value. Everything that was native to the horse has been lost and remade repeatedly in its evolution, including the horse itself. What matters is what lasts. Through its own roundabout history, the horse is still here.
CHAPTER 2
RETURN OF A NATIVE
Two runners walked onto the sun-bleached plaza of Turquoise Pueblo, in what are now the hills south of Santa Fe, New Mexico, one day in the summer of 1680. Young and lean, their feet strung with simple yucca-fiber sandals and powdered with dust from the miles they had covered on the trail, they asked to see the le
ading men of the village and especially the war chief. They carried a message that would change the course of the West forever—and also the course of America’s wild horses.
At the time, the idea of America was still far, far away from the dry hills of the Southwest. The colonies that would become the United States were barely holding onto a few harbors on the East Coast, focused on growing tobacco and executing accused witches. Along the Rio Grande Valley in New Mexico, the native Pueblo tribes had their own culture far removed from the East. They had been growing corn and squash in the powdery soil for centuries. Turquoise Pueblo had prospered as a center of trade in pottery, corn, and semiprecious stones. Over the generations, families had added adobe rooms, one and two stories tall, with fat walls of mud brick, until clusters stood in crooked bunches around a series of oblong plazas. It was one of dozens of pueblos that clung to the land along the Rio Grande, where springs were reliable and soil was good. The tribes followed a calendar of feasts and dances tied to a religion of indigenous spirits: the snake dance, the deer dance, the bean-planting dance. Except for the coming of droughts, little had changed for a very long time.
Then the Spanish came. Conquistadors were the first to arrive, starting with Francisco Vázquez de Coronado in 1540. And though they often left havoc in their wake, they didn’t linger long. Spanish settlers started to arrive in 1598, bringing herds of goats, sheep, cattle, and horses. They built Santa Fe, just a day’s run to the north. But it was the Catholic priests who moved to Turquoise Pueblo in 1635 that the runners had come to discuss. The priests had come bent on ridding the natives of their religion. When they arrived, they built a church atop a cluster of adobes and renamed the pueblo, calling it San Marcos, in honor of Saint Mark the Evangelist. They brought livestock and useful skills like weaving, which the locals welcomed, but they also demanded labor and tribute from the Pueblos, who often had little to spare. And they insisted on strict adherence to Catholicism.
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