They included two unique footprints: one made by an ankylosaur, a herbivorous armored dinosaur, and the other by a carnivorous theropod. Theropods are three-toed predators that include tyrannosaurs. Fiorillo’s team has only recorded two such tracks from a theropod here.
“I’m very excited because it allows us to do statistical analysis with robust data,” said a member of Fiorillo’s team, Yoshitsugu Kobayashi, a professor of paleontology at Japan’s Hokkaido University Museum. “With a few [prints], it’s like you’re sharing a dinosaur whisper, but if you have a large number, it’s like yelling. The dinosaurs are telling us something.”
The team is collecting data to explain how the huge reptiles were able to survive 75 million years ago in a climate that was more like present-day Seattle or Portland, Oregon. A humid, rainy climate and a relatively mild climate don’t seem ideal for multi-ton reptiles, but dinosaurs thrived here, Fiorillo said.
Fiorillo, the executive director of the New Mexico Museum of Natural History and Science, has spent 10 field seasons at Aniakchak. The area has intrigued him since he first discovered a dinosaur footprint here in 2002. “Having walked this couple of miles, there’s a really remarkable frequency of footprints on the beach and on the cliffs,” Fiorillo said, “and I’d be It’s kind of hard to think of that kind of density in the abundance of tracks” elsewhere.
Most of the footprints from about 75 million years ago in the late Cretaceous were made by hadrosaurs, which were duck-billed herbivores. Dinosaur remains and ancient soil samples informed a study published in April in the journal Geosciences. showed that mean annual precipitation had more to do with structuring habitat selection than the average annual temperature among the dinosaurs that roamed Alaska. The study compared the team’s findings not only from Aniakchak Bay, but also from work on Alaska’s North Slope and in Denali National Park and Preserve.
During the late Cretaceous, Aniakchak was not much further south than it is today, so this team has returned here almost every year since 2016 to piece together a more complete picture of how dinosaurs were able to survive here.
“We don’t have a lot of high-resolution dating on this section” of rocks, said Paul McCarthy, head of the Department of Geosciences at the University of Alaska, Fairbanks, who specializes in ancient soils, or paleosols.
At Aniakchak, the geologist is focusing on a 300-meter-thick (328-yard-thick) section of layered sedimentary rock. “So we know the age of the 300-meter section,” he said, but what’s missing is a layer, or layers, within that section that can help provide more detail about how and when the climate here changed.
“It’s really impossible without knowing exactly how long each individual segment represents,” McCarthy said.
On a hike through the arctic dinosaur tracks in the Alaskan reserve
This outcrop, however, offers other details that allow the team to gain specific information about the dinosaurs and their habitat preferences.
“As you go back in time within this section, we can compare who’s walking to the plants, the soils, and whether they’re in a floodplain or an estuary” or somewhere else, McCarthy said.
One end of a roughly three-mile-long stretch of coastline is littered with tracks made by juvenile hadrosaurs. The rocks indicate that the area was once an estuary, where a river emptied into a tidal flat. At the other extreme, most tracks were placed in an exposed intertidal zone by fully grown adult hadrosaurs.
Nicknamed “the birthplace of storms”, Aniakchak Bay offers something new to Fiorillo with each visit. Where mounds of seaweed had come to rot on the beach last year, swathes of black sand took over this summer. The storms here are dramatic enough to move rocks the size of a vehicle, and the rocks seem to change shape as thick sheets of rain give way to intermittent sunlight.
Fiorillo and his team will present some of their findings at the annual meeting of the Geological Society of America in Denver. The four-day event begins on October 1. 9.
“And then we’ll see what new questions come up as we really start to look at the data and then think about the next year,” Fiorillo said.