A significant discovery in far northwestern Alaska has unveiled a trove of dinosaur tracks, fossilized plants, and tree stumps, providing new information about the climate and movements of ancient animals approximately 100 million years ago.

A theropod track lies in rock near the west bank of the Kukpowruk River. Credit: Anthony Fiorillo / University of Alaska Fairbanks

On January 30, an international team of scientists, led by paleontologist Anthony Fiorillo, shared their discoveries in the journal Geosciences. Fiorillo, who conducted research in Alaska while at Southern Methodist University and now serves as the executive director of the New Mexico Museum of Natural History and Science, collaborated closely with University of Alaska Fairbanks geology professor Paul McCarthy and graduate student Eric Orphys, among others.

Their research, focused on the Nanushuk Formation, an outcropped layer of sedimentary rock dating back to the mid-Cretaceous Period, provided insights into the environmental conditions of that era, particularly as it relates to the formation of the Bering Land Bridge connecting Asia and North America.

McCarthy said: “The mid-Cretaceous was the H๏τtest point in the Cretaceous.” By examining the fossilized remains, including approximately 75 dinosaur tracks found in the Coke Basin area along the Kukpowruk River, the team pieced together a snapsH๏τ of life in a warmer Earth.

A fossilized standing tree trunk approximately 2 feet in diameter is rooted in floodplain mudstone and sandstone in the Nanushuk Formation in northwest Alaska. Credit: Paul McCarthy / University of Alaska Fairbanks

The Nanushuk Formation, ranging from 94 to 113 million years old, offered a glimpse into a high-laтιтude ecosystem during a time of elevated global temperatures. Fiorillo remarked on the abundance of dinosaur footprints in the area, providing a vivid picture of an ancient landscape.

Of particular interest were the relative frequencies of different dinosaur species, with bipedal herbivores dominating the track record at 59%. Fiorillo noted the presence of fossil bird tracks, suggesting a similarity in warm paleoclimate conditions to those observed today in the Arctic, where nearly half of North America’s shorebirds breed during the summer months.

Carbon isotope analysis of wood samples indicated a high precipitation rate, estimated at about 70 inches annually, during the mid-Cretaceous Period. This finding aligns with global precipitation patterns ᴀssociated with the Cretaceous Thermal Maximum, a period approximately 90 million years ago characterized by significantly higher temperatures than today.

McCarthy’s expertise in fossil soils helped interpret the ancient environment, revealing details such as river channels, flood deposits, and swampy areas. The research also underscored the site’s location, which was 10 to 15 degrees laтιтude farther north during the mid-Cretaceous than today.

Fiorillo emphasized the significance of the discovery in expanding our understanding of life in high laтιтudes during the time of dinosaurs, stating, “This puts a new dot on the map and tells us there’s a lot here, and it fits into the bigger picture.”

More information: Fiorillo, A.R.; McCarthy, P.J.; Shimer, G.; Suarez, M.B.; Takasaki, R.; Chinzorig, T.; Kobayashi, Y.; O’Sullivan, P.; Orphys, E. (2024). New Dinosaur Ichnological, Sedimentological, and Geochemical Data from a Cretaceous High-Laтιтude Terrestrial Greenhouse Ecosystem, Nanushuk Formation, North Slope, Alaska. Geosciences, 14, 36. doi.org/10.3390/geosciences14020036