100 million years ago, dinosaurs lived in Interior Alaska. A research team went looking for them.

A three-man research team spent three weeks exploring more than 100 miles of Yukon riverbanks this summer to find out more about how dinosaurs lived in the region during the Early Cretaceous. (Emily Schwing/KYUK)

Over the course of three weeks, scientists recorded more than 90 sites where dinosaurs left their footprints along the middle section of the Yukon River. It’s the first time researchers dug so deep into the region’s ancient history.

Paleontologists Tony Fiorillo and Yoshitsugu Kobayashi spent many hours considering the details of footprints left behind by at least half a dozen ancient species.

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Yoshitsugu Kobaysahi, a paleontology professor from Hokkaido University in Japan, points to a dinosaur footprint, left behind 100 million years ago along the bank of the Yukon River. (Emily Schwing/KYUK)

The most common footprints this team found here along the Yukon River this summer were plant-eating dinosaurs that made three-toed prints. Fiorillo and Kobayashi also found footprints left behind by a four-toed, armored ankylosaur.

For his part in the research, Kobayashi, who is a professor at Japan’s Hokkaido University, brought a lot of tools. He uses a technique called photogrammetry to create a 3D image of the fossils. This kind of imagery can help parse out finer details human eyes could miss. He also used a drone to fly over sections of the riverbanks that hold clues about the ancient landscape.

This kind of research is kind of like reading a book and filling in the details. The various dinosaur footprints indicate who the characters in the story are, but at least one of those characters also raised some questions. Nearly 100 million years ago, a species Fiorillo couldn’t immediately identify left a large print with three long, slender toes behind.

Tony Fiorillo (in orange) and Yoshitsugu Kobayashi puzzle over the imprint of dinosaur skin, preserved in a chunk of gray siltstone. The two wonder if the rock isn’t also a preserved dinosaur footprint. (Emily Schwing/KYUK)

Once he returns to his office at the New Mexico Museum of Natural History and Science, Fiorillo will dig through literature and other museum archives to figure out what kind of ancient species left its mark here.

Halfway through the trip, the team stumbled upon a stretch of riverbank about the length of a football field. It was littered with large sandstone blocks that were covered in footprints left by at least two shorebird-like species. Fiorillo was floored by the find: at least 16 blocks covered in the same footprints.

“This must have been a place that they found something to do, like lots of food,” Fiorillo said.

The next day brought another interesting find: a series of small, knobby bumps on a dark gray siltstone that gave Fiorillo and Kobayashi pause. It was a dinosaur skin imprint. They said that the imprint indicates that this environment is also ripe for the preservation of bones.

In all, the team recorded more than 90 track sites left behind by at least half a dozen different ancient species. So many discoveries that both Fiorillo and Kobayashi nearly ran out of pages in their hard-backed yellow field notebooks.

“I was starting to wonder, what am I going to do if I run out of pages? But I never had a field notebook this full,” Fiorillo said.

Kobayashi laughed. He said that he was also running out of space.

“So my figures, drawings, and letters are getting smaller and smaller,” he said.

This summer’s work informs a larger body of research, nearly a quarter century’s worth, on how large reptiles survived this far north. Kobayashi said that the story isn’t yet fully told.

“So once we get back and we get the data together, then we will have another question to ask. More than one, probably,” Kobayashi said. “This stretch of river, just one chapter of the book. We know there are more outcrops down the river. So we try to understand this chapter, and if there’s any holes left unsaid, we’re going to come back.”

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