This article originally appeared in High Country News. “These aren’t the right kind of rocks,” Tony Fiorillo said, pointing at the jagged pink and black stones along Alaska’s Yukon River. The sun blazed down on Fiorillo on the 14th day of a 16-day expedition. A paleontologist and the executive director of the New Mexico Museum of Natural History and Science, Fiorillo was looking for rocks twice as old as the ones he was standing on, alongside the wide, silty yet sparkling Yukon River. The rocks he aimed to find were from the Cretaceous Era, when dinosaurs roamed this part of Alaska in abundance. Paleontologists such as Fiorillo have long suspected that the area would be rich with fossil evidence, but this was the first time a team had set out to thoroughly survey the area. Fiorillo and his two colleagues, the geologist Paul McCarthy and the paleontologist Yoshitsugu Kobayashi, had spent the past two weeks snapping countless photos and penciling endless observations into field notebooks. A few days earlier, they’d stumbled upon a rock face …