Western North America is a dinosaur paleontologist's wonderland, home to some of the most famous and well-studied dinosaurs spanning nearly all of the Mesozoic Era. The Late Cretaceous dinosaurs of Montana and Alberta include familiar duckbills, horned dinosaurs, tyrannosaurs, and smaller theropods like dromaeosaurs and troodontids.
The Prince Creek Formation of Alaska's North Slope was laid down approximately 70 million years ago, corresponding to the uppermost beds of the Judith River and Two Medicine Formations of Montana and Alberta. The Formation is made up of sand and siltstones laid down by rivers that ran from the incipient Brooks range across a coastal plain north to the Arctic Ocean. Although the Mesozoic was warmer than today, northern Alaska did experience fairly cold winters and seasonal snowfall, with an average winter temperature of 2 C (36 F). This is similar to Prince Rupert, BC, Canada, or Copenhagen, Denmark today. Additionally, then as now, northern Alaska experienced periods of winter darkness with the associated cold temperatures.
The dinosaur fauna of the Prince Creek Formation is made up of members of familiar North American dinosaurs including horned ceratopsids like Pachyrhinosaurus, duckbilled hadrosaurs like Ugrunaaluk, a small tyrannosaur known as Nanuqsaurus, and teeth from several relatively small sickle-clawed theropods. Sickle-clawed theropods, known as deinonychosaurs (terrible claw lizards), include the relatively stout dromaeosaurids like Dromaeosaurus, Deinonychus, and Velociraptor, and relatively slender troodontids like Troodon and Saurornithoides. Additionally, based on numbers of teeth recovered, it seems like Troodon was the most common theropod in the Prince Creek Formation, making up nearly 2/3 of all specimens. This is in stark contrast to what's seen in Montana, where Troodon makes up only about 6% of the theropod specimens.