Nanuqsaurus
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''Nanuqsaurus'' (meaning "
polar bear The polar bear (''Ursus maritimus'') is a hypercarnivorous bear whose native range lies largely within the Arctic Circle, encompassing the Arctic Ocean, its surrounding seas and surrounding land masses. It is the largest extant bear specie ...
lizard") is a
genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...
of
carnivorous A carnivore , or meat-eater (Latin, ''caro'', genitive ''carnis'', meaning meat or "flesh" and ''vorare'' meaning "to devour"), is an animal or plant whose food and energy requirements derive from animal tissues (mainly muscle, fat and other sof ...
tyrannosaurid Tyrannosauridae (or tyrannosaurids, meaning "tyrant lizards") is a family of coelurosaurian theropod dinosaurs that comprises two subfamilies containing up to thirteen genera, including the eponymous ''Tyrannosaurus''. The exact number of genera ...
theropod Theropoda (; ), whose members are known as theropods, is a dinosaur clade that is characterized by hollow bones and three toes and claws on each limb. Theropods are generally classed as a group of saurischian dinosaurs. They were ancestrally c ...
known from the
Late Cretaceous The Late Cretaceous (100.5–66 Ma) is the younger of two epochs into which the Cretaceous Period is divided in the geologic time scale. Rock strata from this epoch form the Upper Cretaceous Series. The Cretaceous is named after ''creta'', the ...
period (early Late
Maastrichtian The Maastrichtian () is, in the ICS geologic timescale, the latest age (uppermost stage) of the Late Cretaceous Epoch or Upper Cretaceous Series, the Cretaceous Period or System, and of the Mesozoic Era or Erathem. It spanned the interval from ...
stage)
Prince Creek Formation The Prince Creek Formation is a geological formation in Alaska with strata dating to the Early Maastrichtian stage of the Late Cretaceous. Dinosaur remains are among the fossils that have been recovered from the formation.Weishampel, David B; et a ...
of the North Slope of Alaska, United States. It contains a single
species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...
, ''Nanuqsaurus hoglundi'', known only from a partial
skull The skull is a bone protective cavity for the brain. The skull is composed of four types of bone i.e., cranial bones, facial bones, ear ossicles and hyoid bone. However two parts are more prominent: the cranium and the mandible. In humans, the ...
and multiple undescribed postcranial and teeth elements.


Discovery and naming

In 2006, at the Kikak-Tegoseak Quarry, in
North Slope Borough The North Slope Borough is the northernmost borough in the US state of Alaska and thus, the northernmost county or equivalent of the United States as a whole. As of the 2020 census, the population was 11,031. The borough seat and largest city i ...
in the north of
Alaska Alaska ( ; russian: Аляска, Alyaska; ale, Alax̂sxax̂; ; ems, Alas'kaaq; Yup'ik: ''Alaskaq''; tli, Anáaski) is a state located in the Western United States on the northwest extremity of North America. A semi-exclave of the U.S., ...
, fossils were found of a medium-sized theropod, with an estimated skull length of . These were first referred to ''
Gorgosaurus ''Gorgosaurus'' ( ; ) is a genus of tyrannosaurid theropod dinosaur that lived in western North America during the Late Cretaceous Period (Campanian), between about 76.6 and 75.1 million years ago. Fossil remains have been found in the Can ...
'' and later to ''
Albertosaurus ''Albertosaurus'' (; meaning "Alberta lizard") is a genus of tyrannosaurid theropod dinosaurs that lived in western North America during the Late Cretaceous Period, about 71 million years ago. The type species, ''A. sarcophagus'', was app ...
''. After preparation in the
Perot Museum of Nature and Science The Perot Museum of Nature and Science (shortened to Perot Museum) is a natural history and science museum located in Dallas, Texas in Victory Park. The museum was named in honor of Margot and Ross Perot. The current chief executive officer of ...
(Dallas Museum of Natural History) it was recognized these represented a species new to science. The
holotype A holotype is a single physical example (or illustration) of an organism, known to have been used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of several ...
, 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 The maxilla (plural: ''maxillae'' ) in vertebrates is the upper fixed (not fixed in Neopterygii) bone of the jaw formed from the fusion of two maxillary bones. In humans, the upper jaw includes the hard palate in the front of the mouth. The t ...
; a partial skull roof including partial parietals, frontals and a right laterosphenoid; and the front of the left
dentary In anatomy, the mandible, lower jaw or jawbone is the largest, strongest and lowest bone in the human facial skeleton. It forms the lower jaw and holds the lower tooth, teeth in place. The mandible sits beneath the maxilla. It is the only movabl ...
. The specimen is from a fully mature individual, as it has a smooth nasal contact. ''Nanuqsaurus'' was first described and named by Anthony R. Fiorillo and Ronald S. Tykoski in
2014 File:2014 Events Collage.png, From top left, clockwise: Stocking up supplies and personal protective equipment (PPE) for the Western African Ebola virus epidemic; Citizens examining the ruins after the Chibok schoolgirls kidnapping; Bundles of wat ...
. The
type species In zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the species that contains the biological type specimen ...
is ''Nanuqsaurus hoglundi''. The generic name is derived from the Iñupiaq word for "
polar bear The polar bear (''Ursus maritimus'') is a hypercarnivorous bear whose native range lies largely within the Arctic Circle, encompassing the Arctic Ocean, its surrounding seas and surrounding land masses. It is the largest extant bear specie ...
", ''nanuq'', and the
Greek Greek may refer to: Greece Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group. *Greek language, a branch of the Indo-European language family. **Proto-Greek language, the assumed last common ancestor ...
word ''sauros'', meaning "lizard". The specific name honors the philanthropist Forrest Hoglund, for his work on philanthropy and cultural institutions.


Description

In its initial description, ''Nanuqsaurus'' was estimated to have been about long, about half the length of ''
Tyrannosaurus rex ''Tyrannosaurus'' is a genus of large theropod dinosaur. The species ''Tyrannosaurus rex'' (''rex'' meaning "king" in Latin), often called ''T. rex'' or colloquially ''T-Rex'', is one of the best represented theropods. ''Tyrannosaurus'' live ...
''.Molina-Pérez & Larramendi 2016. ''Récords y curiosidades de los dinosaurios Terópodos y otros dinosauromorfos'', Larousse. Barcelona, Spain p. 259 Its weight has been estimated to be . This diminutive size was postulated by Fiorillo and Tykoski as being an adaptation to its high-latitude habitat. 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 ''Albertosaurus'' (; meaning "Alberta lizard") is a genus of tyrannosaurid theropod dinosaurs that lived in western North America during the Late Cretaceous Period, about 71 million years ago. The type species, ''A. sarcophagus'', was app ...
'' based on undescribed adult-sized teeth and postcranial elements. Some of the undescribed postcranial elements scale to around in length, described comparable to a juvenile ''
Tarbosaurus ''Tarbosaurus'' ( ; meaning "alarming lizard") is a genus of tyrannosaurid dinosaur that flourished in Asia about 70 million years ago, at the end of the Late Cretaceous Period, considered to contain a single known species, ''Tarbosaurus bataa ...
''. Larger sizes are estimated at in length. ''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 . Classified as a tyrannosaurine, ''Nanuqsaurus'' is diagnosed by: a thin, rostrally forked, median spur of the fused parietals on the
dorsal Dorsal (from Latin ''dorsum'' ‘back’) may refer to: * Dorsal (anatomy), an anatomical term of location referring to the back or upper side of an organism or parts of an organism * Dorsal, positioned on top of an aircraft's fuselage * Dorsal co ...
skull roof The skull roof, or the roofing bones of the skull, are a set of bones covering the brain, eyes and nostrils in bony fishes and all land-living vertebrates. The bones are derived from dermal bone and are part of the dermatocranium. In comparati ...
that overlaps and separates the frontals within the
sagittal crest A sagittal crest is a ridge of bone running lengthwise along the midline of the top of the skull (at the sagittal suture) of many mammalian and reptilian skulls, among others. The presence of this ridge of bone indicates that there are exceptiona ...
, frontals with a long, rostrally pointed process separating the prefrontal and lacrimal facets and that the first two dentary
teeth A tooth ( : teeth) is a hard, calcified structure found in the jaws (or mouths) of many vertebrates and used to break down food. Some animals, particularly carnivores and omnivores, also use teeth to help with capturing or wounding prey, tear ...
are much smaller than the dentary teeth behind them.


Classification

Phylogenetic analysis of the Tyrannosauridae finds ''Nanuqsaurus'' to be a close relative of ''Daspletosaurus'' and ''Tyrannosaurus'' within Tyrannosaurinae. Below is a cladogram illustrating the relationships of the Tyrannosauridae:


Paleobiology

According to paleontologists, about 70 million years ago northern Alaska was a part of an ancient subcontinent called
Laramidia Laramidia was an island continent that existed during the Late Cretaceous period (99.6–66 Ma), when the Western Interior Seaway split the continent of North America in two. In the Mesozoic era, Laramidia was an island land mass separated from A ...
and experienced cold weather and extreme changes in the amount of daylight during the year, with seasons in which food was not readily available. Prey availability likely would have increased substantially during the summer, but then declined in the dark winter, leaving predators with little to eat. Fiorillo and Tykoski stated that this lack of food might explain ''Nanuqsauruss unusually small size for an advanced tyrannosaur, as a large animal cannot survive on scarce resources. ''Nanuqsaurus'' may have evolved a smaller size because of the decrease in year-round food supply, caused by the colder temperatures. In contrast, it was also found that the normal length of ''Troodon'' was 50% larger in Alaska compared to more southerly areas, possibly because a larger eye size allowed it to hunt more effectively in low-light conditions. However, Druckenmiller ''et al.'' state that the holotype of ''Nanuqsaurus'' represents a younger individual, based on the physical evidence of undescribed teeth and postcranial remains or larger individuals closer in size to other North American tyrannosaurids like ''Albertosaurus sarcophagus'' which is in length. This contradicts the original interpretation of ''Nanuqsaurus'' being a dwarf tyrannosaurid being 5-6 meters in length.


Paleoecology

The holotype specimen assigned to ''Nanuqsaurus'' comes from the
Maastrichtian The Maastrichtian () is, in the ICS geologic timescale, the latest age (uppermost stage) of the Late Cretaceous Epoch or Upper Cretaceous Series, the Cretaceous Period or System, and of the Mesozoic Era or Erathem. It spanned the interval from ...
age Prince Creek Formation. At an age of 71–68 
million years ago The abbreviation Myr, "million years", is a unit of a quantity of (i.e. ) years, or 31.556926 teraseconds. Usage Myr (million years) is in common use in fields such as Earth science and cosmology. Myr is also used with Mya (million years ago). ...
, the Kikak-Tegoseak Quarry region Prince Creek Formation dates to the early Late Maastrichtian. An average age found in dating rocks from the formation is 69.1 ± 0.3 million years ago, so it is likely that ''Nanuqsaurus'' is from around that age. The formation is along the Colville River on the North Slope Borough, and is made up of alluvial sediments. It is one of a few dinosaurs to live at very high-latitude areas. ''Nanuqsaurus'' lived alongside many other dinosaurs in the Prince Creek formation region during the Edmontonian faunal stage in a climate that was around 10 to 12°C during summer months and -2°C ± 3.9°C during the winter months. Other animals alongside ''Nanuqsaurus'' include an unnamed
leptoceratopsid Leptoceratopsidae is an extinct family of neoceratopsian dinosaurs from Asia, North America and Europe. Leptoceratopsids resembled, and were closely related to, other neoceratopsians, such as the families Protoceratopsidae and Ceratopsidae, bu ...
, the hadrosaurid ''
Edmontosaurus ''Edmontosaurus'' ( ) (meaning "lizard from Edmonton") is a genus of hadrosaurid (duck-billed) dinosaur. It contains two known species: ''Edmontosaurus regalis'' and ''Edmontosaurus annectens''. Fossils of ''E. regalis'' have been found in rocks ...
'' (similar to ''E. regalis''), an unnamed
lambeosaurine Lambeosaurinae is a group of crested hadrosaurid dinosaurs. Classification Lambeosaurines have been traditionally split into the tribes or clades Parasaurolophini ('' Parasaurolophus'', ''Charonosaurus'', others (?).) and Lambeosaurini (''Cor ...
, an unnamed thescelosaurine (mentioned to be similar to '' Parkosaurus'' and ''
Thescelosaurus ''Thescelosaurus'' ( ; ancient Greek - (''-'') meaning "godlike", "marvellous", or "wondrous" and (') "lizard") was a genus of small neornithischian dinosaur that appeared at the very end of the Late Cretaceous period in North America. It was a ...
''), an unnamed
orodromine Orodrominae is a subfamily of thescelosaurid dinosaurs known from the Cretaceous of North America and Asia. Distribution Orodromines were a mostly North American based group with fossils from Canada and United States only. ''Albertadromeus'', as ...
(mentioned to be similar to ''
Orodromeus ''Orodromeus'' (meaning "Mountain Runner") is a genus of herbivorous orodromine thescelosaurid dinosaur from the Late Cretaceous of North America. Only one species is known, the type species ''Orodromeus makelai''. Discovery and naming The rem ...
''), the
ceratopsid Ceratopsidae (sometimes spelled Ceratopidae) is a family of ceratopsian dinosaurs including ''Triceratops'', ''Centrosaurus'', and ''Styracosaurus''. All known species were quadrupedal herbivores from the Upper Cretaceous. All but one species are k ...
'' Pachyrhinosaurus perotorum'', the
pachycephalosaurid Pachycephalosauria (; from Greek παχυκεφαλόσαυρος for 'thick headed lizards') is a clade of ornithischian dinosaurs. Along with Ceratopsia, it makes up the clade Marginocephalia. With the exception of two species, most pachycephal ...
''
Alaskacephale ''Alaskacephale'' was a genus of pachycephalosaurid dinosaur from the Prince Creek Formation, that lived in the early Maastrichtian stages of the Late Cretaceous (around 71 to 69 million years ago). Discovery ''Alaskacephale'' was named by Robe ...
'', a large troodontid referred to the dubious genus ''
Troodon ''Troodon'' ( ; ''Troödon'' in older sources) is a wastebasket taxon and a dubious genus of relatively small, bird-like dinosaurs known definitively from the Campanian age of the Late Cretaceous period (about 77  mya). It includes at least ...
,'' the dromaeosaurid ''
Dromaeosaurus ''Dromaeosaurus'' (, "running lizard") is a genus of dromaeosaurid theropod dinosaur which lived during the Late Cretaceous period (middle late Campanian and Maastrichtian), sometime between 80 and 69 million years ago, in Alberta, Canada and the ...
'', the dromaeosaurid ''Richardoestesia'' (similar to ''R. isosceles''), an unnamed saurornitholestine, an unnamed ornithomimosaur, and multiple
avialans Avialae ("bird wings") is a clade containing the only living dinosaurs, the birds. It is usually defined as all theropod dinosaurs more closely related to birds (Aves) than to deinonychosaurs, though alternative definitions are occasionally use ...
. 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.


See also

*
Timeline of tyrannosaur research This timeline of tyrannosaur research is a chronological listing of events in the history of paleontology focused on the tyrannosaurs, a group of predatory Theropoda, theropod dinosaurs that began as small, long-armed bird-like creatures with ela ...


References

{{Taxonbar, from=Q15933442 Tyrannosaurids Late Cretaceous dinosaurs of North America Monotypic dinosaur genera Fossil taxa described in 2014 Maastrichtian genus extinctions Maastrichtian genus first appearances Maastrichtian life Paleontology in Alaska Taxa named by Anthony Fiorillo