I wasn’t crazy about the height. There we were, one paleontologist who might have been a mountain goat, his two assistants, and me, scrabbling up a mountainside of tilted and crumbling rock strata—or what my companions called “bedding planes.” Loose gravel and rock dislodged by our feet bounced all the way to the glint of streambed in the canyon’s crease below. I tried not to look down as I followed the others in diagonal ascent, and I thanked my new boots and their grippy soles.

Straight out, the view was enough to stop me in my tracks—past the steep gray mountainsides to the green, softening-toward-yellow alpine slopes beyond, and then the farther rocky mountains, all fiery yellows and reds under a high overcast. I could so clearly see something I’d just learned—the geological difference between where I was and where I had been that morning, two parts of Denali National Park. When I’d left the park road to hike up Tattler Creek, I’d walked back through time. The colorful Polychrome Mountains are volcanic, from magma-spewing events 40 to 50 million years ago. But the gray rock of the Cantwell Formation in which I now stood was considerably older, formed during the Late Cretaceous period some 70 million years ago from river and lake sediments deposited in a basin. That basin, later, was lifted by tectonic pressures, tilted, and eroded.

“Rock!” Another hunk of mountain bounced past me.

The mountain goat in our lead, Tony Fiorillo, had zeroed in on a particular ledge and was poking his way along it, examining its underturned face. A paleontologist from Dallas’s Museum of Nature and Science, Fiorillo has worked in Alaska for many years and specializes in high-latitude dinosaur ecosystems. On this trip, he and his two assistants had gotten chased out of their planned study area elsewhere in the park by an aggressive grizzly and so had returned to Tattler Creek to further document what was becoming a major location of dinosaur fossils.

“The candy store,” Fiorillo called it. This area—one of several along the Cantwell Formation in the northeast part of the park—“is the paleontological equivalent of a candy store,” he’d told me when I—a writer visiting the park through its artist-in-residence program—joined him along the creek. Fiorillo was the proverbial kid in the candy store, as excited about every rock on every ledge as any four-year-old let loose among jars and packages of sweets. Now, he was kneeling and squinting and feeling, studying what was embossed in ancient mud. It looked, he called to us, like the track of a “baby” theropod, but—more exciting—a track next to it might belong to a pterosaur. After consultation with the other two—Thomas Adams, a doctoral student who does 3-D laser scanning of dinosaur footprints, and Sarah Venator, a National Parks Service technician—Fiorillo set to work mixing compounds to make a resin cast of the two tracks together.

I sheltered in a protected area below them, still focused on not looking down.

~

The oft-told story has entered the realm of legend: In 2005 a geology professor, Paul McCarthy from the University of Alaska Fairbanks, was teaching students field mapping (that is, how to observe, analyze, and record geologic features in the field) in Denali Park. At an outcrop of the Cantwell Formation, he stopped to explain that that kind of Cretaceous sedimentary rock commonly preserves dinosaur tracks and that they should keep an eye out. At that time, dinosaur footprints had been discovered on Alaska’s North Slope and in Aniakchak National Monument on the Alaska Peninsula, far to the south, but nowhere in interior Alaska. McCarthy had no sooner finished his sentence than two of the students pointed to a spot not far from his gesturing hand and asked, “Like this one?”

That grizzly-sized track, of a three-toed dinosaur known as a theropod, was later removed from its exposed location along a stream and displayed at the Murie Science and Learning Center near the park’s entrance. At the university, Susi Tomsich, one of the two alert students, is now a Ph.D candidate and co-author of a number of scientific papers related to understanding the environment of the Cantwell Formation when dinosaurs roamed. The geology department prominently features on its webpage a photo of that first dinosaur track with the promotional words “discovered by students.”

The unambiguous track looks like a giant bird foot.

~

Theropods. I’d never even heard of them before my trip to Denali and was trying not to confuse them with pteropods, or “winged feet,” tiny swimming marine snails I’d been learning about in another context. (Theropod translates to “beast foot” in the Greek.) Now I’d seen several of their tracks in place and had even learned to distinguish them from other tracks we’d been examining.

Back down in the main valley, before we’d headed up a side canyon, the energetic Fiorillo—a slim, well-tanned man in faded blue jeans stained on the knees from kneeling among blueberries—showed me my first dinosaur footprint. Amongst jumbles of other rocks and boulders that had fallen, washed, or been ice-shoved into the valley and were surrounded by the last blooms of dwarf fireweed, one was shaped into three large, smooth, unnatural-looking lobes.

“They’re all through here,” Fiorillo enthused. “Once we knew what to look for—it just doesn’t stop.”

I rested my hand on a sun-warmed rock toe. This was no ordinary fossil, no mere leaf or shell print in rock; a dinosaur had walked here. To hold that rock was not quite like grabbing a dinosaur by the toe, but the sensation was ticklishly related. I was not in a museum or a roped-off tourist attraction, and I was not looking at a photograph; here was the solid, physical manifestation of a very large near-mythic animal that had once—so very long ago—not only lived, but lived here.

I expect I knew less about dinosaurs (“terrible lizards”—I knew that much) than the average seven-year-old, but Fiorillo, patient teacher that he was, paused his trek to give me a short course in Alaska Dino Basics.

The rock we were looking at was the three-toed track, about a foot long, of a hadrosaur (“bulky lizard”), a duck-billed, sometimes horned, plant-eating dinosaur that grazed in large herds and has been called “the cow of the Cretaceous.” The adult animals (depending on the species) could range from ten to forty feet long. They had powerful hind legs, smaller front legs, and thick tails. They generally walked on all fours.

Some seventy million years ago, towards the end of the Cretaceous period but before the cataclysm (generally agreed by scientists to have been a giant asteroid hit near today’s Yucatan Peninsula) that resulted in the extinction of all dinosaurs as well as much other life on our planet, one of those hadrosaurs living in this northern place had stepped in mud or other soft sediments and left a hind footprint behind. That imprint had later filled with sand or other material harder than the mud, and when the mud eroded away, the cast of the print—the rock we were looking at—was left. “The fossil is the infill,” Fiorillo explained.

The rock casts were examples, Fiorillo, said, of “trace fossils”—fossilized evidence of animal behavior. “These can help tell us how the animals lived—the tracks as a data set to complement bones found elsewhere. When they’re found with other fossils—like horsetails or tree cones—that tells us more about what kind of environment the dinosaurs lived in.”

And what was especially valuable, he said, was that those dinosaurs lived right here—or very close to here—in what is now interior Alaska. While older Alaska rocks originated elsewhere and moved in on blocks pushed by colliding continental plates, the Cantwell Formation rocks formed in place, after mountains eroded into a basin and their sediments accumulated in layers. The mountains we were now in were only pushed up later, elevating and twisting what had been a braided river and lake topography. “These dinosaurs were Alaskan,” Fiorillo said. “They weren’t hijacked tectonically. We have an opportunity to study an ancient polar ecosystem in a warm climate.” That climate, at a “greenhouse” time in Earth’s history, was temperate, perhaps like that of the present-day Pacific Northwest. Winters would have been marked by cold but not frigid temperatures and by snow—as well as by the low light and darkness typical of northern latitudes.

The dinosaur tracks get the most attention from the public, but the larger value lay in studying the full ecosystem preserved in the Cantwell Formation. Other trace fossils found among the dinosaur prints include plants (from ferns and horsetails to the cones of Metasequoia trees), birds (tracks and the marks of beaks probing into mud), fish, burrowing invertebrates (worms and crayfish), even the impressions of scaly dinosaur skin. The numerous fossil bird tracks in Denali, along with being the first of the Cretaceous period found in Alaska and the most northern known to date, present a record of diversity—one of the most diverse fossil bird records yet discovered in the world. Fiorillo and his colleagues have classified one bird track, belonging to a creature larger than a great blue heron, as a new species: Magnoavipes (“big bird track”) denaliensis. The crayfish burrows are interesting because the nearest living crayfish today are found a thousand miles farther south. What it all means is that Alaska’s polar region during the late Cretaceous period supported significant biodiversity. “It’s all here,” Fiorillo said, referring to the biodiversity. “It is just phenomenal.”

~

We headed up a side canyon and all stopped at another track, a bulbous protrusion on a larger slab of mudstone. This was one Fiorillo hadn’t recorded before, and he took a GPS reading, photographs, and then a full page of descriptive notes. Just in this valley, he told me, he’d so far documented about a hundred tracks—many more elsewhere in the park and probably thousands of trace fossils of all kinds.

Venator drew Fiorillo’s attention to another track.

“Tell me what you see,” he said to her, “and then I’ll tell you what I see.”

“Toe, toe,” Venator pointed. “And this part’s broken off.”

“I was trying to see a hadrosaur,” Fiorillo said. “I’ll buy that. This”—he pointed to another mark—“I don’t know about.”

They talked some more, decided they had a single track of a hadrosaur but not a good enough one to document.

Higher, Adams was waiting with a theropod track next to a tree cone fossil. I was beginning to develop my own dinosaur eye, and could easily pick out the three long toes—narrower than those of the hadrosaurs we’d examined below.

Fiorillo had recorded the track and cone on a previous trip, but he took more photos and then we all sat on a ledge and ate our sandwiches.

The theropod, I learned, was a meat-eater, a predator of the hadrosaurs. At least the Denali theropods are thought to have been. Just as “hadrosaur” refers to a large group of plant-eating dinosaurs, “theropod” refers to a large group, or sub-order, distinguished by its bipedal walk on strong legs, bird-like clawed feet, small arms with grasping claws, and big tail for countering its weighty head and neck. Theropods are thought to have been fast and agile and to have had good eyesight. They ranged from chicken-size to huge—and included the famed Tyrannosaurus rex. Their fossils have been found all over the world.

In Denali, judging from their track sizes, adult theropods were commonly about nine feet long and stood three feet at the hip. From the trace fossils found so far, it’s not possible to narrow them into more specific taxa. On Alaska’s North Slope, where bones have been recovered, four species of theropods have been identified—all of them known from other parts of North America.

Linkages between theropods and modern birds have long been studied, and one theropod branch is considered ancestral to birds. At a minimum, many characteristics associated with birds were present in theropods before birds evolved; these included— besides the three-toed foot—hollow bones, a backward-pointing pelvis, and a wishbone in the wrist that allowed a sideways flex and quick snatching motion—a motion almost identical to the flight stroke of modern birds. Some theropods wore feathers.

~

The day was getting late. We’d inspected numerous tracks as well as the fossils of plants and crayfish burrows and had reached high and higher ledges. I left Fiorillo and his crew perched on the mountainside, applying pink resin to bumps on ancient rock, and headed back down the canyon.

But before I left, Fiorillo told me a little about why the possible pterosaur (“winged lizard”) track was so exciting. The year before, he and a colleague had documented a “hand” print from a pterosaur, establishing for the first time that those dinosaur relatives, the earliest vertebrates known to have evolved powered flight, had been present in Cretaceous Alaska. Pterosaurs not only flew, but were the largest flying animals ever to have lived; Fiorillo estimated the Denali one to have had a wingspan of 25 feet. Pterosaurs had digital appendages at their elbow-bends where the wing folds, and rested on both hands and feet when on land—an attribute that, along with air sacs in their wing membranes, might have helped (by providing a launching mechanism) such a large animal fly. If in fact Fiorillo had now found a pterosaur footprint, that evidence would help build a bigger picture of the animal’s presence in the northern ecosystem. Its presence next to a “baby” theropod track was a bonus.

The day before, the team had made molds of a theropod track and then a “baby” hadrosaur foot and hand together. Multiple fossils in the same piece of stone tell a better story than a single fossil alone; a line of tracks from a single animal can tell about its stride, and other combinations tell what lived together or might have been eaten. All through the Cantwell Formation, groups of hadrosaur tracks had been found together, cementing the knowledge that they lived in herds and—based on the many sizes together—that young received extended care by adults.

For all the trace fossils thus examined, Fiorillo and his colleagues had found just one small, non-descript bone in the Cantwell Formation. This is in contrast to the other Alaska area where Fiorillo has done extensive work—the North Slope, where dinosaur bones have been aplenty. Fiorillo expects they’re there in Denali to be found. He told me, “My thoughts on why no masses of bones have been found is that we’ve still only looked at a small percentage of the exposed rock in the park. One animal can leave many tracks in its lifetime, so the odds favor discovery of many tracks first.” Compared to the softer rock farther north, the hard rock in the Cantwell Formation makes tracks easy to see.

The rock quality explained why the area we were in was so fossiliferous. Fossiliferous: my favorite new word.

When I reached the main fork, near where Fiorillo had shown me the day’s first dinosaur track, I detoured to a site he’d told me about, known as “the dance floor.”

I had no trouble finding it on my own. Just beside the path a large rock wall angled out, and the lower surface of it was a rumpled mess. Or that’s what I would have thought before my very recent education. I might have thought it looked like something volcanic, an uneven surface formed by the flow of liquid rock. Now, I knew better. I could see what Fiorillo had described as “like one of those Arthur Murray dance illustrations, with the footprints showing you how to foxtrot.” I could make out a few clear, three-toed tracks, and then it looked to me like there’d just been a lot of big clumsy feet all squishing around on the same soft ground, one footprint obliterating another. I imagined the edge of a waterhole, and a herd of hadrosaurs gathered to drink, or a bank along a stream and the herd thundering past, chased by theropods. After the herd passed, or after many animals took turns coming to drink or to cross a waterway, something—a flood? a landslide?— had covered over the surface, filled and sealed it. Mountains had lifted, mountains had eroded.  Seventy million years, give or take a few million, passed.

Other people had come to see the dance floor. Their boots had worn a track along the base of the wall; their boots had scattered the larger rock shards and ground the smaller into a smooth surface.

I walked up and down that track, studying the wall. I looked closely at one embossment. It looked like a pile of, well, nasty turds, like something a bear that had been eating vegetation might have left behind. It stood out from the other rock to which it was attached, its own abundant and neat assemblage. I was pretty sure it was what the paleontologists call a coprolite—fossilized feces.

~

I took my time returning to the road, in a dinosaur daze of thought and emotion. A silver-colored marmot waddling beside the stream stared at me near-sightedly and wrinkled its nose. Dall sheep like snow patches hung on a far mountain. Juncos and warblers darted through the willows. On a knoll covered with blueberries, I stopped to pick some, stepping around berry-studded bear poop. I passed two burdened backpackers headed to the high country.

Tourists come to Denali primarily to see “the mountain” and the living megafauna—the “big five” bears, wolves, sheep, caribou, and moose. Now, it seemed to me, the park had a new and important role—not just to care for and showcase today’s magnificent wild environment but to preserve and teach us about the past. Dinosaurs are popular, especially with children, because they’re large, fierce (in myth if not fact), and extinct. That is, you get to be thrilled by them without being in any actual danger.

Dinosaurs can’t threaten us, but extinction surely can. As the world warms—and as the Arctic warms disproportionately—we would do well to think about what a warmer Arctic might look like. Fiorillo had said this: “For those concerned about a warming Arctic, the fossils here provide us clues about what that Arctic might look like.” I was one of those concerned. The fossil finds might give us those climate clues, but a warming climate was not going to give us that ancient ecosystem. Nor was it going to favor the current ecosystem, in all its complexity, its finely tuned evolutionary rightness. How will things change in a warmer Alaska? What adaptation mechanisms might help with survival? What migrations might occur? What species might disappear first, or continue longer, or flourish? Less cold, same darkness—who will be the winners and the losers? How will shifts in today’s ecological balance work their way through the whole system?

What can we humans do, now that we understand what our heavy tread has done not just to the Earth’s surface and its other living inhabitants but to the systems that support life as we know it, the Earth’s atmosphere, the ocean’s chemistry?

We might ask and attempt to answer those questions.

Alternatively, we can take the long view—the really long view.

It’s been 65 million years since the dinosaurs and much else—more than 50 percent of all animal species living at that time—went missing. The Earth continued; life recovered. It’s just that dinosaurs didn’t evolve again; mammals filled in the emptied niche. And here we are, now, just one more charismatic species, occupying the Earth for our moment in time. After us: other life, algal or floral, skeletal or spongy, with feet or fins or slinky twists, with large brains or small or none at all. The enduring Earth will bury in its seas and lift into new mountains the footprints—literal and otherwise—of Homo sapiens, our “wise man.”