Walking in Their Footsteps By Amy Leinbach Marquis
Dinosaur prints in Denali National Park and Preserve reveal a prehistoric ecosystem.
There are certain footprints you expect to see in Denali National Park and Preserve in Alaska, like those of wolves, bears, caribou, or the hiker who trekked the same trail earlier that morning.
Now you can add dinosaurs to the list.
Scientists had been looking for fossil remains for a few years, but snow and ice limited their search to the warm summer months, and the size and geography of the park made it difficult to look beyond paved areas. Finally, in June 2005, a geology class from University of Alaska Fairbanks stumbled upon a large footprint in Cantwell formation—a layer of rock nearly 8,000 meters thick that was originally thought to have formed in the Tertiary period, after the mass extinction of dinosaurs. Studies of other imprints from prehistoric plants and fossilized pollen made it clear that this layer was, in fact, a single page in a potential encyclopedia of dinosaur fossils.
Soon after the first footprint was discovered, Dr. Anthony Fiorillo, curator of earth sciences at the Dallas Museum of Natural History, and others from the Park Service and University of Wyoming, discovered a second dinosaur print and bird tracks from the same age. Research intensified, and the resulting findings began painting a picture of the Denali of old: theropods, bipedal meat-eaters that range from the size of a chicken to a towering Tyrannosaurus rex; hadrosaurs, duck-billed vegetarians from the ornithod group; and prehistoric wading birds that resembled modern-day members of the sandpiper family. Now the park contains nearly 50 sites with prehistoric prints.
But it's not the footprints alone that really excite scientists. It's the way the prints have provided a glimpse of a prehistoric ecosystem in action. Theropod and hadrosaur prints together hint at a predator-prey relationship. And the bird prints, accompanied by smaller, dimpled imprints, illustrate an ancient foraging ritual: The birds used their beaks to probe riverbeds, the earliest evidence of birds' feeding behavior from that period.
According to Phil Brease, a geologist at Denali National Park and Preserve, these discoveries unearthed the first evidence of dinosaur existence in interior Alaska. Previous finds had occurred only on the fringes, like the North Slope, and the Matanuska Valley in south central Alaska.
Most of the research within Denali National Park and Preserve has occurred in places that are relatively easy to get to, as the park can't afford the luxury of helicopter travel to more remote sites. Fiorillo, Brease, and others generally begin their search for new fossils by visiting sites with fossilized plants, hoping to find evidence of flora that existed in the same age as the dinosaurs.
To the untrained eye, the prints resemble a typical rock surface, jagged and irregular. But like experts tracking wolves or bears, fossil-hunters are adept at finding patterns in the rock, including the telltale claws of an early reptile. When they find a print, they measure it, photograph it from various angles, and eventually create a latex mold used to render a three-dimensional footprint in fiberglass. Intact prints offer clues about the animals' size, hinting at physical information as detailed as height and hip width. One area contains so many fossil footprints that Fiorillo describes it as a prehistoric "dinosaur dance floor."
Students and scientists itching to play a role in the research can sign up through the park's Murie Science and Learning Center, which offers natural science courses in the field. It's still a little early for the park to offer interpretive programs to the general public, but the fiberglass casts will soon be on display in the park's visitor center. Visitors will even get to see one fossil up close: A fossilized footprint discovered on an isolated rock was poised to fall into Igloo Creek and might have proven too tempting to vandals, so it was removed to become part of a display in coming months.
For now, Brease plans to conduct more extensive lab analysis to narrow down the time range, and Fiorillo may look to publish the findings in scientific journals. And of course, the search for even more fossils will continue. Although the fossilized footprints are a big step, so to speak, they're only considered trace fossils—indirect evidence of an animal's presence—which means there's a good chance that actual fossilized bones are still out there somewhere, just waiting to be discovered.
For photos of the discoveries and more information on Denali's Murie Science and Learning Center, visit www.murieslc.org.
Amy Leinbach Marquis is assistant editor for National Parks magazine.
