Nanuqsaurus (meaning "polar bear lizard") is a genus of tyrannosaurine theropod dinosaur known from the Late Cretaceous period (middle Maastrichtian age) Prince Creek Formation of the North Slope of Alaska, having lived roughly 70-68 million years ago.

Before the formal description of Nanuqsaurus, numerous tyrannosaurid teeth were known from the Kogosukruk Tongue of the Prince Creek Formation and were first referred to the genus Gorgosaurus.

In 2006, within the North Slope Borough of Alaska, the fossilized remains of what appeared to be a medium-sized theropod were located at the Kikak-Tegoseak Quarry of the Prince Creek Formation.

[3] Initially, Nanuqsaurus was estimated to have been about 5–6 meters (16–20 ft) long, a metric based on the holotype specimen, putting the animal at about half the length of Tyrannosaurus rex.

Below is a cladogram illustrating the relationships of the Tyrannosauridae:[11]Gorgosaurus libratus Albertosaurus sarcophagus Qianzhousaurus sinensis Alioramus remotus Alioramus altai Teratophoneus curriei Dynamoterror dynastes Lythronax argestes Nanuqsaurus hoglundi Thanatotheristes degrootorum Daspletosaurus torosus Daspletosaurus horneri Zhuchengtyrannus magnus Tarbosaurus bataar Tyrannosaurus rex A 2023 thesis argued that its taxonomic validity and phylogenetic position is poorly resolved, and that the taxon is a nomen dubium.

This evidence suggests that both Nanuqsaurus and its likely prey items remained in the paleo-Arctic yearlong and would have had to cope with ~120 days of constant winter darkness each year, as opposed to resorting to migration to escape the harsh conditions.

In contrast to the contemporary large herbivores Edmontosaurus and Pachyrhinosaurus, which apparently preferred coastal lowland and upland environments respectively, Nanuqsaurus appears to have been fairly ubiquitous throughout the Prince Creek landscape.

Due to the cooler conditions of this habitat, many otherwise common ectothermic clades lack representation entirely in the Prince Creek Formation, suggesting that all the animals that did thrive in these extreme latitudes were indeed endotherms to some degree.