Nanuqsaurus (meaning "polar bear lizard") is a genus of carnivorous tyrannosaurid theropod known from the Late Cretaceous period (early Late Maastrichtian stage) Prince Creek Formation of the North Slope of Alaska, United States. It contains a single species, Nanuqsaurus hoglundi, known only from a partial skull and multiple undescribed postcranial and teeth elements.
In its initial description, Nanuqsaurus was estimated to have been about 5–6 meters (16–20 ft) long, about half the length of Tyrannosaurus rex.[1][2][3] Its weight has been estimated to be 500–900 kilograms (1100–2000 lbs).[1][3] This diminutive size was postulated by Fiorillo and Tykoski as being an adaptation to its high-latitude habitat.[4] However, later studies suggested that its supposed small size was unfounded, and that it was likely similar in size to other North American tyrannosaurids such as Albertosaurus based on undescribed adult-sized teeth and postcranial elements.[5] Some of the undescribed postcranial elements scale to around 7 meters (22 ft) in length, described comparable to a juvenile Tarbosaurus.[6] Larger sizes are estimated at 8–9 metres (26–30 ft) in length.[7]
Nanuqsaurus bears a particularly shaped ridge on its head indicating the carnivore was related to Tyrannosaurus rex. The length of the reconstructed skull, based on the proportions of related animals, is 60–70 cm (24–28 in).[4]
Classified as a tyrannosaurine, Nanuqsaurus is diagnosed by: a thin, rostrally forked, median spur of the fused parietals on the dorsal skull roof that overlaps and separates the frontals within the sagittal crest, frontals with a long, rostrally pointed process separating the prefrontal and lacrimal facets and that the first two dentary teeth are much smaller than the dentary teeth behind them.[4]
In 2006, at the Kikak-Tegoseak Quarry, in North Slope Borough in the north of Alaska, fossils were found of a medium-sized theropod, with an estimated skull length of 600–700 mm (24–28 in). These were first referred to Gorgosaurus and later to Albertosaurus. After preparation in the Perot Museum of Nature and Science (Dallas Museum of Natural History) it was recognized these represented a species new to science.[4] The holotype, DMNH 21461, has been found in a layer of the Prince Creek Formation, dated at 69.1 million years. It consists of a partial skull with a lower jaw, which were found very close together. It contains the nasal branch of the right maxilla; a partial skull roof including partial parietals, frontals and a right laterosphenoid; and the front of the left dentary.[4] The specimen is from a fully mature individual, as it has a smooth nasal contact.[4]
Nanuqsaurus was first described and named by Anthony R. Fiorillo and Ronald S. Tykoski in 2014. The type species is Nanuqsaurus hoglundi. The generic name is derived from the Iñupiaq word for "polar bear", nanuq, and the Greek word sauros, meaning "lizard". The specific name honors the philanthropist Forrest Hoglund, for his work on philanthropy and cultural institutions.[4]