| Nanuqsaurus | |
|---|---|
 | |
| Reconstructed skeleton,Perot Museum | |
Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Clade: | Dinosauria |
| Clade: | Saurischia |
| Clade: | Theropoda |
| Superfamily: | †Tyrannosauroidea |
| Family: | †Tyrannosauridae |
| Subfamily: | †Tyrannosaurinae |
| Genus: | †Nanuqsaurus Fiorillo & Tykoski,2014 |
| Type species | |
| †Nanuqsaurus hoglundi Fiorillo & Tykoski, 2014 | |
Nanuqsaurus (meaning "polar bear lizard") is agenus oftyrannosaurinetheropoddinosaur known from theLate Cretaceous (LatestCampanian age)Prince Creek Formation of theNorth Slope of Alaska. It contains a singlespecies,Nanuqsaurus hoglundi, known from a partialskull and multiple undescribed postcranial and teeth elements.
Before the formal description ofNanuqsaurus, numeroustyrannosaurid teeth were known from the Kogosukruk Tongue of thePrince Creek Formation and were first referred to the genusGorgosaurus.[1] Later, after the locale was understood to be younger than previously thought, the consensus switched to referring to the teeth under the genusAlbertosaurus.[2][3]
In 2006, within theNorth Slope Borough ofAlaska, the fossilized remains of a medium-sized theropod were located at the Kikak-Tegoseak Quarry of thePrince Creek Formation. The material was found to contain multiple fragments of the animal's skull, all of which were collected from the same quarry and found to most likely belong to a single individual. Among the disarticulated fragments preserved were the nasal branch of the rightmaxilla, a fragmentary skull roof including pieces of bothfrontals,parietals, a piece of the rightlaterosphenoid, and a fragment of the leftdentary. These anatomical features were later used to estimate the skull length of the animal, with estimates giving it a length of 600–700 mm (24–28 in).[3] Recent revisions to Radiometric dating now suggest a Latest Campanian age.[4]
It wasn't until after preparation and analysis at thePerot Museum of Nature and Science (Dallas Museum of Natural History) when the AlaskanTyrannosaurid remains were finally recognized to represent a newtaxon as opposed to being synonymous with previousgenera. This prompted the creation of a new genus,Nanuqsaurus, described and named byAnthony R. Fiorillo andRonald S. Tykoski in2014. The initially discovered material, referred to as DMNH 21461, is now recognized as theholotype ofNanuqsaurus. As well as this, the initial discoveries of teeth were placed as more likely to be the remains ofNanuqsaurus as opposed to any other known creature, contrary to the initial proposals of the origin of the teeth.[3]
Thetype species,Nanuqsaurus hoglundi, has itsgeneric name derived from theIñupiaq word for "polar bear",nanuq, and theGreek wordsauros, meaning "lizard". Thespecific name honors the philanthropistForrest Hoglund for his work on philanthropy and cultural institutions.[3]
Initially,Nanuqsaurus was estimated to have been about 5–6 meters (16–20 ft) long, a metric based on theholotype specimen, putting the animal at about half the length ofTyrannosaurus rex.[5][6][7] The length of the same specimen's reconstructed skull, based on the proportions of related animals, was 60–70 cm (24–28 in).[3] Its weight was also estimated to be 500–900 kg (1,100–2,000 lb).[5][7] This diminutive size was postulated by Fiorillo and Tykoski as being an adaptation to its high-latitude habitat.[3] However, later studies tied 13 additional fossil elements across a 20 km stretch of the Colville River to a single theropod taxon. Further, that more recent work suggested that its supposed small size was unfounded and that it was likely similar in size to other North American tyrannosaurids, such asAlbertosaurus which grew up to 8–9 meters (26–30 feet) long, based on undescribed adult-sized teeth and postcranial elements.[8] Some of the undescribed postcranial elements scale to around 7 meters (23 feet) in length, described comparable to a juvenileTarbosaurus.[9] It is estimated that the adultNanuqsaurus specimens would have weighed over 1.9 metric tons (2.1 short tons) based on these recently collected fossils.[10]
Nanuqsaurus would have likely resembled other largetyrannosaurines, such asDaspletosaurus, with both animals being closely related and probably serving similar roles in their respective ecosystems.[11]Nanuqsaurus itself is anatomically diagnosed by the following traits:
Phylogenetic analysis of Tyrannosauridae findsNanuqsaurus to be a close relative ofDaspletosaurus andTyrannosaurus within Tyrannosaurinae. Below is a cladogram illustrating the relationships of the Tyrannosauridae:[11]
A 2023 thesis argued that its taxonomic validity and phylogenetic position is poorly resolved, and that the taxon is anomen dubium.[12] A 2024 study recoveredAsiatyrannus from theNanxiong Formation ofSouth China to be in apolytomy with the North AmericanNanuqsaurus. These results are displayed in thecladogram below:[13]
Analysis of material attributed toNanuqsaurus and other Alaskan dinosaurs from the same environment has resulted in thePrince Creek Formation being recognized as having preserved an exceptionally high percentage of developmentally young dinosaurs when compared to the amount of families represented in the formation. Material from young dinosaur specimens, includingbirds, has been determined to be present from seven different majorclades, or 70% of all the recognized families of the quarry. The families in question areHadrosauridae,Thescelosauridae,Leptoceratopsidae,Ceratopsidae,Tyrannosauridae,Dromaeosauridae,Troodontidae, andAvialae. This evidence suggests that bothNanuqsaurus 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. It is proposed that the animals would likely have laid their eggs toward the beginning of the constant daylight period, around the month of April, allowing time for the eggs to incubate in the relative heat of this part of the year.[8][14]
Nanuqsaurus lived alongside many other dinosaurs during what is referred to as theEdmontonian faunal stage of the Latest Campanian. Having resided at an estimated 80°–85°N paleolatitude, isotopic analysis ofoxygen-18 ratios in tooth enamel indicate cool mean annual temperatures near or just above 0 °C (32 °F).[15]
Other animals that lived alongsideNanuqsaurus include the following: an unnamedleptoceratopsid, the hadrosauridEdmontosaurus (similar toE. regalis),[16] an unnamedlambeosaurine, an unnamedthescelosaurine (mentioned to be similar toParkosaurus andThescelosaurus), an unnamedorodromine (mentioned to be similar toOrodromeus), theceratopsidPachyrhinosaurus perotorum, thepachycephalosauridAlaskacephale, a large troodontid assigned to the dubious genusTroodon, the dromaeosauridsDromaeosaurus andSaurornitholestes, along with an unnamedsaurornitholestine, an unnamedornithomimosaur, and multipleavialans.[8] As well as this, several mammals, including themetatherianUnnuakomys,[17] theeutherianGypsonictops, both an unnamed and namedmultituberculate, the latter beingCimolodon, and finally an indeterminatemarsupial. Due to the cooler conditions of this habitat, many otherwise commonectothermic clades lack representation entirely in the Prince Creek Formation, suggesting that all the animals that did thrive in these extreme latitudes were indeedendotherms to some degree.
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{{cite journal}}: CS1 maint: article number as page number (link)We note that other Prince Creek Formation tyrannosaurid material in the UAMES collection do not support the assertion that Nanuqsaurus is a diminutive, small-bodied tyrannosaur. Rather, adult-sized teeth and isolated postcranial elements suggest an adult body size more closely comparable to other North American tyrannosaurid taxa, such as Albertosaurus sarcophagus.
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