Prosaurolophus—a hadrosaur that grew to twenty-five feet in length and weighed a couple of tons—also found only in late Cretaceous sediments. Everywhere I walked, it seemed, I also found dinosaur eggshells, countless small, black shards resting on the ground and jutting from outcrops. The specimens we recovered by removing hundreds of pounds of overburden—soil and rock lying on top of fossil layers—at the Willow Creek anticline we could collect from a single shovelful of dirt in some parts of the Landslide Butte badlands.
By that time, David Weishampel, a dinosaur paleontologist from the Johns Hopkins School of Medicine, his family, and crew were camping with us along the banks of the Milk River. I had invited David to explore a nearby section of the St. Mary River Formation, which represented upland coastal plain sediments deposited as the seaway receded for the last time during the late Cretaceous. While passing through the area in the early 1900s, Barnum Brown had collected a primitive horned dinosaur related to the Mongolian Protoceratops, which he had named Montanaceratops. David not only found a Montanaceratops, just a hundred yards from Brown's excavation, but also dinosaur egg and embryonic remains, the first ever from the St. Mary River Formation and another indication that green mudstones containing layers of caliche are excellent rocks in which to find such specimens. With David's discovery, and what my crews were uncovering in the uppermost layers of the Two Medicine Formation, I had ample reason to believe that I had come to the right place to test my ideas about parental care among dinosaurs. What's more, Bob and I had witnessed an omen—actually, two of them.
It may surprise you to hear a scientist talking about omens, but those of us who venture beyond the deliberately simplified, highly controlled conditions of the laboratory quickly learn that we are at the mercy of forces and events that lie outside our control—even, at times, beyond the reach of scientific understanding. Somewhat like farming, sailing, or any occupation that brings one into intimate and sustained contact with the elements, scientific fieldwork tends to instill in its practitioners a great respect for the vagaries and complexities of the natural world. Our fortunes, after all, are tied closely to such unpredictable phenomena as the weather. Like farmers and sailors, then, we invent rituals to manage the many uncertainties in our circumstances. This is not to say that when it rains I fall to my knees in the mud and pray that it will stop. But I have to admit that when the downpour does finally cease, I can't help but feel as if a small blessing has been bestowed upon me and my crews. And like farmers and sailors we sometimes indulge in the less-than-precise but nonetheless entertaining art of identifying signs of good fortune, of reading portents of things to come. For Bob and me, that had always meant keeping an eye out for blue herons and pelicans.
Over the years we had encountered so many herons and pelicans in the vicinity of our excavations that we came to expect to see them on a pretty regular basis. If we didn't, if what seemed like an unusually long time passed without our having spotted at least one, especially if our fieldwork wasn't yielding much in the way of interesting fossils, Bob might joke, "We shoulda known better, Jack, we shoulda known." He was especially fond of the pelican. One evening early in the 1986 season—I can't recall exactly when or even how the subject came up—he said that if he died sooner rather than later, his spirit would always remain close by, watching us through the eyes of a big white pelican. "And if I do die," Bob added emphatically, "give me a wake. None of that somber stuff." I remember thinking at the time that were one of us to go early, it would most likely be me. Bob just seemed unstoppable. As a young man he'd survived Hodgkin's disease, one of the first in the country to do that. His passion for fossil collecting was insatiable. He wouldn't think twice about walking twenty miles under a blistering sun or jackhammering limestone for twenty days straight. In camp Bob was a dynamo. Teacher, father figure, keeper of fieldwork stories and traditions, he initiated new crew members into the ways of paleontological excavation as well as into the secrets of living comfortably outdoors. Invariably, Bob was the last one to go to sleep at night and the first to wake in the morning, busily preparing supplies and equipment, filling water containers, getting everyone ready for another long day of digging.
So it was no surprise when early one morning in July, while the rest of the crew slept, Bob poked his head through the opening to my tepee and said, "Hey, Jack, you've got to see this." Living in tepees, by the way, was one of our fieldwork traditions. The structures are portable, fairly easy to set up, and you can cook in them if you have to. Most important, they are superior to all but a few tents in being able to withstand the winds that invariably whip across the high plains of central and eastern Montana. Our 1986 Landslide Butte camp consisted of several tepees pitched on a rise just above the river. Below, close to the bank, we had set up our kitchen tent, where everyone took meals together. And that is where Bob directed my attention when I stepped, a bit groggy, from the shadow world of my tepee into the hazy light of an uncomfortably warm morning.
"Look," he said. "There it is." Down in our kitchen area a great blue heron, evidently having come from the river, was tiptoeing around the tent as if trying not to wake anyone. Bob and I watched the bird for a while. Almost four feet tall, with very long legs and a long neck, the elegant wader seemed unfazed by our presence. In time, though, other members of the crew got up and moved about the camp, making noise. The heron took a couple of quick steps toward the river, unfolded its kite-size wings, and waved them up and down. Within seconds it was a hundred yards upstream, a swiftly receding blue-gray blur.
As if that weren't encouraging enough, about an hour later, during breakfast, a flock of white pelicans soared across the camp, low enough that I could hear the collective whoosh of their wings. Like most everyone, I enjoy the songs of birds, but there is something especially compelling about the sounds of wings in flight, something that tugs at the heart. In the moments when a large-winged bird passes close by one hears, I think, the coming and going of life itself, its lightninglike transience—the sudden rustling of the air, fast-moving shapes glimpsed out of the corner of an eye, followed by utter silence. As quickly as the white pelicans came into view, it seemed, they vanished over the horizon. "Gonna be a good day," Bob pronounced.
And it was, because that was the day I took a close look at Gilmore's datum layer, discovering that the fragments he had thought were the remains of freshwater clams were in fact dinosaur eggshells. Gilmore had chosen that layer of green mudstone, remember, not only because it was easily recognizable—by the fragments it contained—but because it stretched across most of the badlands north of Landslide Butte, providing a universal benchmark against which he could measure the distance and thus age of strata above and below it. In other words, when he misidentified the
The Hypacrosaurus nesting horizon at Landslide Butte. Xs show the nesting horizon; the arrow points to the top of the Two Medicine Formation. (Par Leiggi, reproduced courtesy of the Museum of the Rockies.)
eggshells he also missed the opportunity to see what so extensive a deposit really meant—that the fragments represent an immense nesting horizon, in fact, at a mile long and at least a quarter-mile wide, the largest dinosaur rookery in the Western Hemisphere. Averaging about two feet thick, this broad layer of mudstone actually contains numerous nesting colonies stacked on top of each other and belonging to the Hypacrosaurus we first saw at Lambeosite. The horizon contains thousands of nests, hundreds of embryonic and nestling hypacrosaur bones, and millions upon millions of eggshell fragments mixed together with whole eggs, squashed eggs, and egg clutches.
Apparently a herd of hypacrosaurs, consisting of at least a thousand adults, had gathered repeatedly in the Landslide Butte area to bear their young. Imagine standing on a hill and taking in that scene: twelve-foot-tall, thirty-foot-long crested duck-billed dinosaurs milling about as far as the eye can see. Now imagine this: heavy gray clouds approach from the south, originating somewhere within the Rockies. As they draw closer the sky darkens. It starts to rain, but what falls is not water. It is ash, a cataract of blinding soot and red-hot debris called airfall tuff. As has happened many times during the Cretaceous period, the volcanoes now known as the Adell Mountains, located in west-central Montana, are erupting, once again causing havoc among the dinosaurs that live on the upland coastal plains. And the eruptions will persist for days, perhaps longer.
The adult hypacrosaurs have no choice but to flee the rookery. Using their crests, which are hollow and of a piece with the nasal passage, the dominant males bugle a low-pitched alarm. Instinctively the herd responds, one by one abandoning their nests and moving in one gigantic formation to the east, or the north, away from the deadly fallout. The sound the heavy creatures make as they lumber across the land is thunderous. Soon the herd is engulfed in a cloud of dust. Ash continues to rain down. It seems as if the world is coming to an end. And it is, but only for the unborn and newly hatched dinosaurs left behind. The ash smothers the embryos and nestlings, burying eggs, nests, everything—the entire rookery. Today the rookery lies beneath a layer of rock called ben-tonite, a sediment formed from volcanic fallout. That's how we know what happened to the hypacrosaurs of Landslide Butte.
With the discovery of the Hypacrosaurus rookery, the upper layers of the Two Medicine Formation exceeded my hopes for the 1986 season. But our good fortune didn't end there. Toward the end of August, Carrie Ancell, a preparator who had spent two seasons at the Willow Creek anticline, and I discovered a second assembly of horned dinosaurs identical to those at Dino Ridge Quarry. Located about a mile from the first site, Canyon Bone Bed, as we called the new fossil horizon, comprised the same dark brown, sandy silt-stone, arranged in the same depositional patterns, containing the same carbonized plant debris and remains of freshwater invertebrates, which led Ray Rogers to conclude that it, too, represented a shallow pond where a large group of ceratopsians had gathered during a drought, then died en masse. What was surprising about the new site were the skulls we found. At Dino Ridge Quarry we uncovered only cranial fragments, enough to suggest that they belonged to a new ceratopsian but insufficient to reconstruct the head in detail, enabling us to identify with confidence all the critical differences. Canyon Bone Bed, by contrast, yielded two nearly complete skulls—and one very intriguing puzzle.
The nose horns on most ceratopsians are quite similar. Those of Styracosaurus and Centrosaurus, for example, are long and straight, pointing upward, at a right angle to their snouts, and the same is true of Triceratops. But the nose horn on Einiosaurus, the first skull from Canyon Bone Bed, is short and hooked, curved so far forward that it points downward, toward the ground. What's more, instead of the six spikes fanning out from the neck shield, as is the case with Styracosaurus, the skull has a pair of long spikes that extend backward from its shield. A third distinguishing feature is a small, rounded nub over each eye socket. The nose horn of the second skull, recovered from a lower and therefore older level than Canyon Bone Bed, differs from that of Einiosaurus in that the tip curves ever so slightly backward; otherwise it is long and straight and pitched at a right angle to the snout, very similar to Styracosaurus. Yet, like the first skull, it possesses none of the other identifying cranial features of Styracosaurus. In particular, its neck shield also sports two long horns directed backward, and above the eyes lie bumplike protrusions.
Both skulls are moderate in size—about four feet long—and heavy, particularly when we encased them in plaster jackets, after which they weighed as much as a thousand pounds each, and that posed a problem. We remove most dinosaur fossils from our excavations using either a medical field stretcher or a device conceived and built by Bob, ever the restless gadgeteer. Nicknamed the Dino Wheel, it resembles a stretcher but is made of metal and is supported underneath by a motorcycle wheel riding on a short axle. Much refined over the years, our most recent model can still carry
Bob Makela with one of his field inventions, the Dino Wheel, which can be used by two people to get heavy loads in and out of areas having no roads. (Pat Leiggi, reproduced courtesy of the Museum of the Rockies.)
only about six hundred pounds of fossils. Making matters more difficult, the ceratopsian skulls were located on the face of a fairly steep cliff.
Solution? Call in the cavalry. Well, a modern-day version of the cavalry: the United States Army National Guard. A Huey gunship flew up from Helena, about two hundred miles away, to airlift the dinosaur skulls of Canyon Bone Bed into waiting trucks. For the guard pilots the exercise was an opportunity to practice picking up objects in rough terrain. For me, it was a source of amusement and wonder. The amusing part was watching giant blobs of plaster suspended from steel cables floating over the badlands of Landslide Butte. The wonder was aroused by the mysteries now hidden inside the plaster. That curved horn, especially. It was telling me something. But what exactly?
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