In North America, we generally use native to mean any critter that was here before Christopher Columbus hit land. In recent decades, we have given these native animals special rights, trying to protect them while working to eradicate the invaders. We spend millions of dollars trying to save a black-footed ferret or a sage hen in the West, and millions more building electric fences to keep the Asian carp out of the Great Lakes or kill Asian pythons in the Everglades. Wildlife laws protect the bobcat, but not the feral house cat. We want to preserve an old balance in a world where we have shifted the balance dramatically. I share this desire. I want protection for the natives. As I write this, a thumb-size broad-tailed hummingbird is hovering at a feeder in an old pine above my keyboard. I love seeing such a precise distillation of life so much that I would do nearly anything to protect its annual migration over hundreds of miles along the Rockies.
But what is really native? How long do migrants like the wild horse have to be here before they count? Certainly more than a hundred years, we would all likely agree. But what about a thousand? What about ten thousand? At some point, the label of being invasive must wear off. What is the process through which an animal becomes native? And how do we decide? Those were questions I wanted to start answering with a trip to Bighorn Basin.
As I looked for Professor Rose’s camp, I drove through old beds of sandstone and shale laid down millions of years ago, when this part of Wyoming was a flat, muddy coast that alternated among thick jungle, tropical swamp, and shallow sea. A postcard sent during the era might have looked a lot like the coast of South Carolina. Over millions of years, the area was a depository for silt and muck washed down from the mountains to the west. The layers of sediment made a great Cenozoic layer cake, with bands of hard white sandstone and bands of crumbly shale in colors ranging from milk to gray to dusty mint to clay-pot red. They eventually piled up more than twenty-five hundred feet thick.
Then the whole area was slowly pushed up, between eighty million and thirty-five million years ago. The sea receded to the east. Layers of muck that had piled up and become stone were exposed to the elements as they rose. Eons of wind and rain have whittled them into buttes, mesas, and rumpled shale hills. This ancient, hardened layer cake of jungle muck is called the Willwood Formation. It makes up every hill and draw for miles around. Crush the shale between your fingers and it turns velvety smooth. Set a hard Wyoming wind on it and it fills the air, covering everything with fine dust. Get it wet and it turns into a slippery, sticky, shoe-sucking glop that the paleontologists who have been traipsing these hills for generations call gumbo.
I spotted Rose’s camp about five miles from the highway. It was off in a low draw where occasional moisture in the sand had nurtured a few stunted cottonwoods, which offered a little shade and a buffer from the wind. It was near sunset when I parked on the edge of the camp, and I could see graduate students milling around a dozen tents tucked among giant sage bushes that grew five feet high. One big cooking tent stood in the middle.
The students—sunburned, weary, but otherwise cheerful—were splashing the dust off their faces and arms in plastic basins after a long day in the field. Most of them planned to spend the whole summer here, searching the hills for fossils by day and bringing back their finds at night.
When I got out of my car, Rose came out of the cook tent at a fast walk, hand extended to greet me. He wore a blue Oxford button-down shirt and wire-frame glasses, and had a distinguished gray professorial beard. But this East Coast University look was offset by a wildly battered cowboy hat crowned with a dark band of dirt and sweat and punctuated by a long magpie tail feather that poked from the band. It was a unique mix of starch and grit that only field paleontologists seem to have.
“To most people, this is badlands,” he said, after shaking my hand and ushering me to the edge of the camp where we could see the bare shale hills beyond. “To paleontologists, it is the most valuable land in the world.”
The Willwood has been a destination for researchers for more than a century because its many layers, gently laid down during a period between fifty-five and fifty-two million years ago, record a turning point in history, right after the dinosaurs disappeared, when mammals began to flourish. The period when it formed is called the Eocene Epoch, from the ancient Greek word eos, meaning dawn, because it was the dawn of the modern era. The Bighorn Basin is one of the few places in the world where a large slice of the Eocene is preserved. And it is perhaps the best place to see the beginning of horses.
“Everything is just right here for fossils,” Rose said. Conditions were right millions of years ago to gently bury plants and animals in wet, flat, sediment-rich plains. After that, conditions were just right to bury those plains under more sediment so they could be pressed to make stone and be preserved. More recently, conditions were just right when the tectonic plate that makes up North America began to buckle, slowly uplifting the land. And conditions were just right when erosion removed thousands of feet of newer rock that covered the Willwood. On top of all that, the rain shadow was just right to keep almost all of the ground from being covered by grass and trees, letting wandering paleontologists find their quarry.
“You could not ask for better conditions,” Rose said. Just then, a gust came up and took off his hat, which went bounding through the sage. He added, “Well, I guess a little less wind would be nice.”
Rose grew up in New Jersey, far from the vast Eocene beds of the West. But, as a boy, he had developed an insatiable thirst for collecting—primarily trilobites, sharks’ teeth, and other fossils from the ancient shallow seabed that today makes up much of New Jersey.
“Other kids played baseball,” he said as we sat down for dinner at the camp’s single table. “I had a museum in my basement.”
He first came out to the Bighorn Basin when he was an undergraduate in 1968 and has come back nearly every summer since, earning an MA degree from Harvard University and a PhD from the University of Michigan along the way.
I had contacted him because I wanted to get as close an understanding as I could of the first horses. I wanted to try to see what the first horses looked like and imagine their journey from the dawn of mammals to the present day. But I also wanted to understand how this long history has shaped the recent history of wild horses. We talked a few times by phone, and then he said, “If you really want to get a feel for it, you should just come out to the field.”
Before we turned in for the night, he unrolled a large topographical map to decide where his team would focus the next day. The decades-old sheet was peppered with neat pencil notes showing the dates he had collected in each spot. Some showed two or three passes. Every decade or two, he said, he returns to see if erosion has turned up anything new. His map also acts as the unpublished modern history of the Willwood. Here and there, a few words recorded the dates and places of notable occurrences observed over the decades that broke the normally timeless silence of the badlands: the scorpion bite, the nudist, the madman at the sheep camp.
Several of the pencil inscriptions prompted stories he told the students by the light of the camp lantern. I pointed to one note: The day of 427 jaws. I asked what it meant.
“That was maybe the greatest collecting day we’ve ever had,” Rose said.
Jaws, it turns out, are what Rose’s crew is after. Often, they are all that is left of a mammal after fifty million years. Dying is a pretty brutal process. Even if an animal dies peacefully, it is almost always picked apart by scavengers, the remains scattered and broken and nibbled into oblivion. It is almost astronomically unlikely that a carcass is left intact to be buried. And even then, to be discovered fifty million years later, it has to survive the slow, uncertain process of fossilization, then the uplift of the formation, then erosion. Almost nothing does. But jaws, it turns out, are sturdy, and that is a very lucky thing. More than any other part of the skeleton, jaws carry a wealth of clues about ancient mammals: size, diet, evolutionary lineage, even social structure.
“Full skeletons are pretty to look at but not scientifically valuable,” Rose said. “They don’t tell us much. Jaws tell us a lot.”
Rose now has tens of thousands of jaws in his collection. Over the years, his teams of students have collected so many that they can see how the population changed over millennia and start to describe not just what was in the Bighorn fifty million years ago but also how twenty or so species changed over three million years as the Earth rapidly warmed.
“We can’t do that for animals today,” Rose said that night, right before he turned off the camp lantern. “In some ways we know more about these ancient horses than we know about the animal today.”
At dawn, Rose’s students gathered for coffee and a quick breakfast of fruit and granola, seeking shelter in the cook tent from the sun, which felt searing on the skin at 6 a.m. Amid the clatter of spoons and bowls, Rose, who likes to begin each day by reading a passage from a notable paleontologist, opened a marked page in a book by George Gaylord Simpson, one of the greatest evolutionary biologists of the twentieth century. Rose handed the open book, which detailed Simpson’s explorations of Patagonia, to a student, who began to read:
A 50 MILLION-YEAR-OLD FRAGMENT OF JAW FROM THE FIRST HORSE, HYRACOTHERIUM, IN BIG HORN BASIN, WYOMING.
Fossil hunting is far the most fascinating of all sports. I speak for myself, although I do not see how any true sportsman could fail to agree with me if he had tried bone digging. It has some danger, enough to give it zest and probably about as much as in the average modern engineered big-game hunt, and the danger is wholly to the hunter. It has uncertainty and excitement and all the thrills of gambling with none of its vicious features. The hunter never knows what his bag may be, perhaps nothing, perhaps a creature never before seen by human eyes. Over the next hill may lie a great discovery! It requires knowledge, skill, and some degree of hardihood. And its results are so much more important, more worthwhile, and more enduring than those of any other sport! The fossil hunter does not kill; he resurrects. And the result of his sport is to add to the sum of human pleasure and to the treasures of human knowledge.”1
“Hallelujah, well said!” Rose applauded.
With that, the crew climbed into a mud-splattered 1990 Chevrolet Suburban that had the fossil of an early ancestor of the modern deer, called Diacodexis, stenciled on the side. Rose stomped on the gas pedal and took off with a lurch through the badlands, speeding like someone who had just robbed a bank. The old Suburban bounced and bounded at sixty miles an hour down a narrow dirt track through the desert. As he sped up over a rise, Rose pushed a cassette into the old tape deck in the dash and the speakers blared the theme song for Indiana Jones—Dun da dun-dun, dun da-duuuunnnn!
I gripped the edge of the vinyl seat as the truck flew over rolls and swayed through turns. Rose barely held the loose steering wheel as he flew along. He seemed much more focused on pointing out places where he had gathered fossils than he did on the road. I realized only later, when we stopped at the site where we were going to collect that day, why the distinguished professor drove like such a madman. After more than forty years collecting here, he knew every dip and roll of this country, and knew how much he could push the needle. Also, hunting for Eocene jaws is an agonizingly slow process, requiring sauntering inspection for hours on end. You might cover a mile in a day. Probably less. Do that all day without a little thrill and it could be a very long summer. As George Gaylord Simpson said, fossil hunting should have enough danger to give it zest.
An avid hunter like Rose would probably add that the faster you drive, the sooner you are searching for fossils.
“Horses!” he shouted. He jammed on the brakes. The Suburban skidded to a stop and was enveloped a second later in the gray cloud of dust that had been trailing off the back. As the dust cleared, he pointed to six wild horses on the horizon. We watched them silhouetted in the morning sun. They stood a few seconds, their heads up and ears pricked. Then the lead mare wheeled and disappeared over the horizon. The others followed, dissolving into the badlands.
“Have you ever seen them here before?” I asked. I had no idea wild horses still wandered the Bighorn Basin.
“Oh, lots of them,” Rose said. He had seen horses in varying numbers since he first started coming to the basin in the late 1960s. No one quite knows how far back these horses go. The BLM’s first record of horses here dates back to 1938, when the bureau’s predecessor, the United States Grazing Service, tried unsuccessfully to remove all of them. In the 1940s, one local cowboy claimed to have removed twenty thousand mustangs from the basin with the help of a small plane. But the presence likely goes back much farther, possibly to the Crow and the Shoshone tribes. It was near this area that a few Shoshone became especially skilled at hunting with horses, split from their old tribe, headed east, and became the Comanche. Lewis and Clark had lost some horses not far north of here. It could be their descendants we saw running wild.
The horses we spotted that morning weren’t technically supposed to be there. As I mentioned before, the BLM divides wild horse areas into two types: Herd Management Areas and Herd Areas. Herd Management Areas are places where horses are known to live and have the BLM’s blessing. Local district offices are supposed to manage those areas primarily for the horses. Herd Areas, on the other hand, are places where horses are known to live, but the BLM has decided they should not be there. Those horses are slated for eventual removal. The horses we saw were in a third situation. They were not in an HMA or an HA. They were completely off the map, not known to exist. Truly wild. Maybe they had wandered through the unfenced badlands from the nearest HMA, a dozen miles away. Maybe they had been here for centuries, unnoticed or unnoted by BLM managers. The Bighorn Basin is a rough, lonely place. A lot can hide out in the Willwood.
After the horses galloped away, we drove on, finally stopping at a broad amphitheater of shale and sandstone, completely bare of vegetation. “This is my empire,” Rose said. “Every outcrop in miles I have collected.”
We split up to look for fossils. The graduate students went off in pairs, and I teamed up with Rose. He slipped on his sweat-stained cowboy hat and we started walking. Or, rather, we started ambling. Walking suggests a little too much speed. We shambled, shuffled, dallied, and perused, covering maybe ten feet per minute as our eyes scanned the ground.
We were looking for the telltale glint of teeth. In the fossilization process, white teeth turn nearly black. In a museum, they can look like little bits of onyx, but in the sun of Wyoming they have a glint like the brown glass from a broken beer bottle.
“You find that glint,” Rose said. “And chances are you have found something good.”
The only problem with looking for something that looks like a broken piece of beer bottle in Wyoming is that cowboys have been coming out to the middle of nowhere to shoot beer bottles here for a very long time. I spent a lot of the day bending down, only to find the remains of a distant Saturday night.
If we had been sashaying through the Bighorn Basin fifty-five million years ago, the scene would have looked fantastically different. It might have looked a lot like the coast of Laos or Brazil. The basin, now at about four thousand feet, then sat at sea level next to a shallow sea that once covered much of the Great Plains. Though the latitude was about the same as it is now, the climate was tropical. Paleontologists refer to this time as “greenhouse Earth.” There was no ice, even at the poles. Palm trees and crocodiles extended above the Arctic Circle. Forests dominated the planet. Grass, which in modern times came to cover most of the Earth, was relegated to a few small clearings. The prickly brush of windy Wyoming was then steamy jungle with canopies of ginkgoes, sycamore, hickory, and medicine wood rising over a soggy understory of thick green. Turtles of all sizes paddled the slow streams, squirrel-size primates skittered up rough forest trunks.
In the undergrowth, a giant, flightless bird called Gastornis stood more than six feet tall on ostrichlike legs. It had a sicklelike beak fifteen inches thick, w
hich might have been an oversize nutcracker for an omnivore or might have been a lethal neck cracker for a predator, used to grab and crush smaller animals. If it was a neck cracker, its typical meal might have been the first-ever horses.
The first horse was not much bigger than a cat and as slender as a deer, with a back hunched a bit like a rabbit’s and dainty legs like those of a deer. It was called Hyracotherium (pronounced “heer-a-co-theer-ee-um”). It was likely a bounder, not a runner. It had four small toes on its front feet and three on its back. Each toe ended in a nimble hoof, like the trotter of a piglet. Its delicate muzzle was made to nibble tender leaves and berries near the forest floor. A lot remains unknown about this ancient animal, but one thing Rose knows for sure: There were a heck of a lot of them. He finds more Hyracotherium jaws in the Willwood than any other fossil. It dominated the forest.
The first fossil of Hyracotherium wasn’t found anywhere near Bighorn Basin. If it had been, it likely would not be called Hyracotherium, a name that George Gaylord Simpson, who spent decades hunting fossil horses, described as “a jawbreaker that is not likely to win so many friends.”
Wild Horse Country Page 4