They included two unique footprints: one made by an ankylosaur, an armored herbivorous dinosaur, and the other by a carnivorous theropod. Theropods are three-toed predators that include tyrannosaurs. Only two of these theropod tracks were recorded by Fiorillo’s team here.
“I’m very excited because it allows us to do statistical analysis with robust data,” said Fiorillo team member Yoshitsugu Kobayashi, a professor of paleontology at the Hokkaido University Museum in Japan. “With a few [prints], it’s as if you share a dinosaur whisper, but if you have a large number of them, it’s like screaming. Dinosaurs tell us something.
The team is collecting data to explain how huge reptiles were able to survive 75 million years ago in a climate more like present-day Seattle or Portland, Oregon. A humid, rainy climate and relatively temperate weather don’t seem ideal for multi-tone reptiles, but dinosaurs thrived here, Fiorillo said.
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Fiorillo, executive director of the New Mexico Museum of Natural History and Science, spent 10 seasons in the field at Aniakchak. The area has intrigued him since he discovered a dinosaur footprint here in 2002. “Walking those few miles, there’s just a really remarkable frequency of tracks on the beach and in the cliffs,” Fiorillo said. , hard to think of that kind of density in the abundance of tracks” elsewhere.
Most of the footprints dating from around 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. He showed that average annual precipitation had more to do with structuring habitat selection than average annual temperature in 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.
At the end of the Cretaceous, Aniakchak wasn’t much further south than it is today, so this team has returned here nearly every year since 2016 to piece together a more complete picture of how dinosaurs may have survived here.
“We don’t have a lot of high-resolution dating in this section” of rocks, said Paul McCarthy, head of the geosciences department at the University of Alaska Fairbanks, which specializes in ancient soils, or paleosols.
At Aniakchak, the geologist is focusing on a section of layered sedimentary rock 300 meters thick (328 yards thick). “So we know the age of the 300-meter section,” he said, but what’s missing is one or more layers in that section that can help provide more detail about how and when the climate has changed here.
It’s “really impossible without knowing exactly how long each individual segment is,” McCarthy said.
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This outcrop, however, offers other details that allow the team to gain insight into the dinosaurs and their habitat preferences.
“As you go through time in this section, we can compare who is walking towards the plants, the soils and whether they are in a floodplain or an estuary” or in another location, said McCarthy.
One end of a strip of coastline about three miles long is littered with tracks left by juvenile hadrosaurs. The rocks indicate that the area was once an estuary, where a river flowed into a tidal flat. At the other end, the majority of the tracks were made in an intertidal zone exposed by adult adult hadrosaurs.
Nicknamed “the birthplace of storms”, Aniakchak Bay offers something new to Fiorillo with every visit. Where heaps of kelp had washed up to rot on the beach last year, swaths of black sand have taken over this summer. The storms here are dramatic enough to move vehicle-sized boulders, and the boulders seem to change shape as thick sheets of rain give way to intermittent sunshine.
Fiorillo and his team will present some of their findings at the Geological Society of America’s annual meeting in Denver. The four-day event begins on October 9.
“And then we’ll see what new questions arise as we really start analyzing the data and thinking about next year,” Fiorillo said.