Nanuqsaurus

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.{{Cite journal |last1=Fiorillo |first1=Anthony R. |last2=Gangloff |first2=Roland A. |date=2010-08-24 |title=Theropod teeth from the Prince Creek Formation (Cretaceous) of northern Alaska, with speculations on Arctic Dinosaur paleoecology |url=https://www.tandfonline.com/doi/abs/10.1671/0272-4634(2000)020[0675:TTFTPC]2.0.CO;2 |journal=Journal of Vertebrate Paleontology |volume=20 |issue=4 |page=675 |language=en |doi=10.1671/0272-4634(2000)020[0675:TTFTPC]2.0.CO;2 |issn=0272-4634|url-access=subscription }} Later, after the locale was understood to be younger than previously thought, the consensus switched to referring to the teeth under the genus Albertosaurus.{{Cite book |last1=Ryan |first1=Michael J. |url=https://books.google.com/books?id=OWpQW_WhPAsC&dq=Fiorillo+AR,+McCarthy+PJ,+Flaig+PP,+Brandlen+E,+Norton+DW,++et+al+..+(2011)+Paleontology+and+paleoenvironmental+interpretation+of+the+Kikak-Tegoseak+Quarry+(Prince+Creek+Formation:+Late+Cretaceous),+northern+Alaska:+a+multi-disciplinary+study+of+a+high-lat&pg=PA456 |title=New Perspectives on Horned Dinosaurs: The Royal Tyrrell Museum Ceratopsian Symposium |last2=Chinnery-Allgeier |first2=Brenda J. |last3=Eberth |first3=David A. |date=2010 |publisher=Indiana University Press |isbn=978-0-253-35358-0 |language=en}}{{Cite journal| last1 = Fiorillo| first1 = A. R. | author-link = Anthony Fiorillo| last2 = Tykoski | first2 = R. S. | author-link2 = Ronald Tykoski| year = 2014| title = A Diminutive New Tyrannosaur from the Top of the World| editor-last = Dodson| editor-first = Peter| editor-link = Peter Dodson| journal = PLoS ONE| volume = 9| issue = 3| pages = e91287| doi = 10.1371/journal.pone.0091287| ref = {{sfnRef|Fiorillo & Tykoski|2014}} | pmid=24621577 | pmc=3951350| bibcode = 2014PLoSO...991287F | doi-access = free}}

In 2006, within the North Slope Borough of Alaska, the fossilized remains of a medium-sized theropod were located at the Kikak-Tegoseak Quarry of the Prince 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 right maxilla, a fragmentary skull roof including pieces of both frontals, parietals, a piece of the right laterosphenoid, and a fragment of the left dentary. These anatomical features were later used to estimate the skull length of the animal, with estimates giving it a length of {{convert|600|–|700|mm|in|abbr=on}}. Radiometric dating of nearby rock suggests that the fossils were deposited roughly 68 to 70 Ma.{{Cite book |last1=Conrad |first1=James E. |url=https://books.google.com/books?id=GhOD4bhgnksC&pg=PA1 |title=Age of Tephra Beds at the Ocean Point Dinosaur Locality, North Slope, Alaska, Based on K-Ar and 40Ar/39Ar Analyses |last2=McKee |first2=Edwin H. |last3=Turrin |first3=Brent D. |date=1992 |publisher=U.S. Government Printing Office |language=en}}File:Nanuqsaurus hoglundi.png

File:Nanuqsaurus at Perot Museum.jpg

It wasn't until after preparation and analysis at the Perot Museum of Nature and Science (Dallas Museum of Natural History) when the Alaskan Tyrannosaurid remains were finally recognized to represent a new taxon as opposed to being synonymous with previous genera. This prompted the creation of a new genus, Nanuqsaurus, described and named by Anthony R. Fiorillo and Ronald S. Tykoski in 2014. The initially discovered material, referred to as DMNH 21461, is now recognized as the holotype of Nanuqsaurus. As well as this, the initial discoveries of teeth were placed as more likely to be the remains of Nanuqsaurus as opposed to any other known creature, contrary to the initial proposals of the origin of the teeth.

The type species, Nanuqsaurus hoglundi, has its generic name 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.

File:Nanuqsaurus.pngInitially, Nanuqsaurus was estimated to have been about {{convert|5|–|6|m|ft|sp=us}} long, a metric based on the holotype specimen, putting the animal at about half the length of Tyrannosaurus rex.Molina-Pérez & Larramendi 2016. Récords y curiosidades de los dinosaurios Terópodos y otros dinosauromorfos, Larousse. Barcelona, Spain p. 259{{cite web |title=New Pygmy Tyrannosaur Found, Roamed the Arctic |url=https://news.nationalgeographic.com/news/2014/03/140313-new-species-dinosaurs-tyrannosaurus-rex-animals-science/ |url-status=dead |archive-url=https://web.archive.org/web/20190412083303/https://news.nationalgeographic.com/news/2014/03/140313-new-species-dinosaurs-tyrannosaurus-rex-animals-science/ |archive-date=12 April 2019 |access-date=11 January 2022 |website=news.nationalgeographic.com}}{{Cite book |last=Paul |first=Gregory S. |title=The Princeton Field Guide to Dinosaurs 2nd Edition |publisher=Princeton University Press |year=2016 |location=New Jersey |pages=114}} The length of the same specimen's reconstructed skull, based on the proportions of related animals, was {{convert|60|–|70|cm|in|abbr=on}}. Its weight was also estimated to be {{convert|500|–|900|kg|lb|abbr=on}}. This diminutive size was postulated by Fiorillo and Tykoski as being an adaptation to its high-latitude habitat. 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 as Albertosaurus which grew up to {{convert|8|-|9|m|ft|abbr=off|sp=us}} long, based on undescribed adult-sized teeth and postcranial elements.{{Cite journal |last1=Druckenmiller |first1=Patrick S. |last2=Erickson |first2=Gregory M. |last3=Brinkman |first3=Donald |last4=Brown |first4=Caleb M. |last5=Eberle |first5=Jaelyn J. |date=2021-06-24 |title=Nesting at extreme polar latitudes by non-avian dinosaurs |journal=Current Biology |language=English |volume=31 |issue=16 |pages=3469–3478.e5 |doi=10.1016/j.cub.2021.05.041 |issn=0960-9822 |pmid=34171301 |quote=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. |doi-access=free|bibcode=2021CBio...31E3469D }} Some of the undescribed postcranial elements scale to around {{convert|7|m|ft|abbr=off|sp=us}} in length, described comparable to a juvenile Tarbosaurus.{{Cite web |title=Nanuqsaurus description by Pat Druckenmiller for Alaska Paleo-Project "Northern Tyrant King" |url=https://www.youtube.com/watch?v=4tScqOtjVGE |website=Youtube| date=21 October 2020 }} It is estimated that the adult Nanuqsaurus specimens would have weighed over {{convert|1.9|MT|ST}} based on these recently collected fossils.{{Cite journal|last1=Wilson |first1=L. N. |last2=Gardner |first2=J. D. |last3=Wilson |first3=J. P. |last4=Farnsworth |first4=A. |last5=Perry |first5=Z. R. |last6=Druckenmiller |first6=P. S. |last7=Erickson |first7=G. M. |last8=Organ |first8=C. L. |year=2024 |title=Global latitudinal gradients and the evolution of body size in dinosaurs and mammals |journal=Nature Communications |volume=15 |issue=1 |at=2864 |doi=10.1038/s41467-024-46843-2 |pmid=38580657 |pmc=10997647 |doi-access=free |bibcode=2024NatCo..15.2864W }}

File:Nanuqsaurus hoglundi size chart.pngNanuqsaurus would have likely resembled other large tyrannosaurines, such as Daspletosaurus, with both animals being closely related and probably serving similar roles in their respective ecosystems. Nanuqsaurus itself is anatomically diagnosed by the following traits:

• 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
• The first two dentary teeth are much smaller than the dentary teeth behind them.

Phylogenetic analysis of Tyrannosauridae finds Nanuqsaurus to be a close relative of Daspletosaurus and Tyrannosaurus within Tyrannosaurinae. Below is a cladogram illustrating the relationships of the Tyrannosauridae:{{Cite journal|last1=Voris|first1=Jared T.|last2=Therrien|first2=François|last3=Zelenitsky|first3=Darla K.|last4=Brown|first4=Caleb M.|date=2020-06-01|title=A new tyrannosaurine (Theropoda:Tyrannosauridae) from the Campanian Foremost Formation of Alberta, Canada, provides insight into the evolution and biogeography of tyrannosaurids|journal=Cretaceous Research|language=en|volume=110|pages=104388|doi=10.1016/j.cretres.2020.104388|bibcode=2020CrRes.11004388V |s2cid=213838772|issn=0195-6671}}File:Nanuqsaurus dentary.png{{clade| style=font-size:90%; line-height:90%

|label1=Tyrannosauridae

|1={{clade

|label1=

|1={{clade

|label1=Albertosaurinae

|1={{clade

|1=Gorgosaurus libratus

|2=Albertosaurus sarcophagus}}

|label2=Tyrannosaurinae

|2={{clade

|label1=Alioramini

|1={{clade

|1=Qianzhousaurus sinensis

|2={{clade

|1=Alioramus remotus

|2=Alioramus altai}} }}

|label2=

|2={{clade

|label1=

|1={{clade

|1=Teratophoneus curriei

|2=Dynamoterror dynastes

|3=Lythronax argestes}}

|label2=

|2={{clade

|1=Nanuqsaurus hoglundi

|2={{clade

|label1=

|1={{clade

|label1=Daspletosaurini

|1={{clade

|1=Thanatotheristes degrootorum

|2={{clade

|1=Daspletosaurus torosus

|2=Daspletosaurus horneri}} }}

|label2=

|2={{clade

|1=Zhuchengtyrannus magnus

|2={{clade

|1=Tarbosaurus bataar

|2=Tyrannosaurus rex }} }} }} }} }} }} }} }} }} }}

A 2023 thesis argued that its taxonomic validity and phylogenetic position is poorly resolved, and that the taxon is a nomen dubium.{{cite thesis|last=Perry|first=Zackary R.|year=2023|chapter=Chapter 1|title=A Reinterpretation of Nanuqsaurus hoglundi (Tyrannosauridae) From the Late Cretaceous Prince Creek Formation, Northern Alaska|degree=MSc|publisher=University of Alaska Fairbanks}} A 2024 study recovered Asiatyrannus from the Nanxiong Formation of South China to be in a polytomy with the North American Nanuqsaurus. These results are displayed in the cladogram below:{{Cite journal |last1=Zheng |first1=Wenjie |last2=Jin |first2=Xingsheng |last3=Xie |first3=Junfang |last4=Du |first4=Tianming |date=2024-07-25 |title=The first deep-snouted tyrannosaur from Upper Cretaceous Ganzhou City of southeastern China |journal=Scientific Reports |language=en |volume=14 |issue=1 |page=16276 |doi=10.1038/s41598-024-66278-5 |issn=2045-2322|doi-access=free |pmid=39054316 |pmc=11272791 |bibcode=2024NatSR..1416276Z }}

{{clade| style=font-size:90%; line-height:90%

|{{clade

|1={{clade

|1=Albertosaurus 65px

|2=Gorgosaurus 85px }}

|label3=Tyrannosaurinae

|3={{clade

|1=Nanotyrannus

|2={{clade

|1=Alioramus spp. 80px

|2=Qianzhousaurus 85px }}

|3={{clade

|1=Lythronax 80px

|2=Teratophoneus 85px

|3={{clade

|1=Asiatyrannus 85px

|2=Nanuqsaurus

|3={{clade

|1=Daspletosaurus spp.

|2={{clade

|1=Zhuchengtyrannus 85px

|2={{clade

|1=Tarbosaurus 85px

|2=Tyrannosaurus

}} }} }} }} }} }} }}|label1=Tyrannosauridae}}

Analysis of material attributed to Nanuqsaurus and other Alaskan dinosaurs from the same environment has resulted in the Prince 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, including birds, has been determined to be present from seven different major clades, or 70% of all the recognized families of the quarry. The families in question are Hadrosauridae, Thescelosauridae, Leptoceratopsidae, Ceratopsidae, Tyrannosauridae, Dromaeosauridae, Troodontidae, and Avialae. 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. 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.{{Cite journal |last1=Herman |first1=Alexei B. |last2=Spicer |first2=Robert A. |last3=Spicer |first3=Teresa E. V. |date=2016-01-01 |title=Environmental constraints on terrestrial vertebrate behaviour and reproduction in the high Arctic of the Late Cretaceous |journal=Palaeogeography, Palaeoclimatology, Palaeoecology |series=Selected papers based on Geological Society of America, Annual Meeting, Theme Session 241, Ancient Polar Ecosystems and Climate History in Deep Time, Denver, Colorado, USA, 30 October 2013. |language=en |volume=441 |pages=317–338 |doi=10.1016/j.palaeo.2015.09.041 |issn=0031-0182|doi-access=free |bibcode=2016PPP...441..317H }}

File:Nanuqsaurus NT small.jpg

Nanuqsaurus lived alongside many other dinosaurs during what is referred to as the Edmontonian faunal stage of the early Late Maastrichtian. Having resided at an estimated 80°–85°N paleolatitude, the area Nanuqsaurus thrived in experienced climatic extremes unlike that experienced by most other dinosaurs. The temperature of this Northern environment would've ranged from around 10 to 12 °C during the warmer months and about -2 °C ± 3.9 °C during the colder months. As well as this, the environment would have faced 120 days of continuous low-light conditions during the Winter. 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.

Other animals that lived alongside Nanuqsaurus include the following: an unnamed leptoceratopsid, the hadrosaurid Edmontosaurus (similar to E. regalis),{{Cite journal |last1=Takasaki |first1=Ryuji |last2=Fiorillo |first2=Anthony R. |last3=Tykoski |first3=Ronald S. |last4=Kobayashi |first4=Yoshitsugu |date=2020-05-06 |title=Re-examination of the cranial osteology of the Arctic Alaskan hadrosaurine with implications for its taxonomic status |journal=PLOS ONE |volume=15 |issue=5 |pages=e0232410 |bibcode=2020PLoSO..1532410T |doi=10.1371/journal.pone.0232410 |issn=1932-6203 |pmc=7202651 |pmid=32374777 |doi-access=free}} an unnamed lambeosaurine, an unnamed thescelosaurine (mentioned to be similar to Parkosaurus and Thescelosaurus), an unnamed orodromine (mentioned to be similar to Orodromeus), the ceratopsid Pachyrhinosaurus perotorum, the pachycephalosaurid Alaskacephale, a large troodontid assigned to the dubious genus Troodon, the dromaeosaurids Dromaeosaurus and Saurornitholestes, along with an unnamed saurornitholestine, an unnamed ornithomimosaur, and multiple avialans. As well as this, several mammals, including the metatherian Unnuakomys,{{Cite journal |last1=Eberle |first1=Jaelyn J. |last2=Clemens |first2=William A. |last3=McCarthy |first3=Paul J. |last4=Fiorillo |first4=Anthony R. |last5=Erickson |first5=Gregory M. |last6=Druckenmiller |first6=Patrick S. |date=2019-11-02 |title=Northernmost record of the Metatheria: a new Late Cretaceous pediomyid from the North Slope of Alaska |url=https://doi.org/10.1080/14772019.2018.1560369 |journal=Journal of Systematic Palaeontology |volume=17 |issue=21 |pages=1805–1824 |doi=10.1080/14772019.2018.1560369 |bibcode=2019JSPal..17.1805E |issn=1477-2019|url-access=subscription }} the eutherian Gypsonictops, both an unnamed and named multituberculate, the latter being Cimolodon, and finally an indeterminate marsupial. 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.

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