Paleontologists investigated dinosaur footprints and large assemblages of fossilized plants. Nanushuk FormationIt extends over much of the northern slope of central and western Alaska, varying in thickness from 1,500 to 250 m (4,921 to 820 ft) from west to northeast.

“For the past 20 years, Alaska has been working on projects that integrate sedimentology, dinosaur paleontology, and paleoclimate indicators,” said Paul McCarthy, a professor at the University of Alaska Fairbanks.

“We've been studying the other three formations, Denali, the North Slope, and southwestern Alaska, and they're about 70 million years old.”

“This new one is in strata that are about 90 million to 100 million years old.”

“What we were interested in looking at rocks from this age is that this is about the same time that people thought the Bering Land Bridge connecting Asia and North America began.”

“We want to know who was using it, how they were using it, and what the circumstances were.”

“The mid-Cretaceous period was the hottest period of the Cretaceous period.”

“The Nanushuk Formation gives us a snapshot of what high-latitude ecosystems look like on a warm Earth.”

The Nanushuk Formation dates from the mid-Cretaceous period, approximately 94 to 113 million years ago, at the beginning of the Bering Land Bridge.

The field survey was conducted between 2015 and 2017, focusing on the Cork Basin, a circular geological feature of the formation.

The basin is located at the base of the Delong Mountains along the Kukpouluk River, approximately 100 km (60 miles) south of Point Rey and 32 km (20 miles) inland from the Chukchi Sea.

In the area, paleontologists found about 75 fossilized footprints and other traces of dinosaurs believed to have lived along rivers and deltas.

“This place had so many dinosaur footprints. One site stands out,” said Dr. Anthony Fiorillo, a researcher at the New Mexico Museum of Natural History and Science.

“We eventually realized that we were walking over an ancient landscape for at least 400 yards (366 meters).”

“In that landscape, we found large upright trees with smaller trees between them, with leaves on the ground. There were footprints on the ground, and there was fossilized feces.”

“We found numerous fossilized tree stumps about 60 centimeters (2 feet) in diameter. It felt like we were walking through a forest that was millions of years old.”

Although the Nanushuk Formation includes rocks of marine and non-marine characteristics and composition, the new study focuses primarily on non-marine sediments exposed along the upper Kukpouluk River.

“One of the things we did in our paper was look at the relative frequencies of different types of dinosaurs,” Dr. Fiorillo said.

“What was interesting to us was that bipedal plant-eating animals were clearly the most common.”

Two-legged plant-eating animals accounted for 59% of all footprints discovered. 17% were four-legged plant-eating dinosaurs, 15% were birds, and 9% were non-avian, mainly carnivorous bipedal dinosaurs.

“One of the interesting things is the relative frequency of bird tracks,” Dr. Fiorillo said.

Carbon isotope analysis of wood samples revealed that the area received approximately 70 inches (178 cm) of rainfall per year.

This record of increased precipitation during the Mid-Cretaceous provides new data supporting global precipitation patterns associated with the Mid-Cretaceous. Cretaceous thermal maximum.

The Cretaceous thermal maximum was a long-term trend about 90 million years ago, during which average global temperatures were significantly higher than today.

“Temperatures were much warmer than today, and perhaps more interestingly, we had a lot of rain,” Dr. Fiorillo said.

a paper Survey results are published in a magazine earth science.

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Anthony R. Fiorillo other. 2024. New dinosaur ichthyological, sedimentological, and geochemical data from the Nanushuk Formation of Alaska's North Slope, a Cretaceous high-latitude terrestrial greenhouse ecosystem. earth science 14(2):36; doi: 10.3390/geosciences14020036