Nanuqsaurus

*Nanuqsaurus* is an extinct genus of tyrannosaurid dinosaur that lived in Alaska during the Late Cretaceous.

## History

*Nanuqsaurus* was discovered at the Kikak-Tegoseak Quarrt of North Slope Borough, Alaska in 2006. Its holotype skull is 600-700 millimeters (24-28 inches) long, first referred to *Gorgosaurus* and later to *Albertosaurus*. After the Perot Museum of Nature and Science had prepared it, it was found to be diagnostic as a new species. The holotype, DMNH 21461, was found in a layer of Prince Creek 69.1 million years of age; it is a partial skull with mandible found close in association, containing the nasal branch of the right maxilla, a partial skull roof (including partial parietals), frontals, the right laterosphenoid and the front of the left dentary. It is an immature individual representing a younger ontogeneic stage .

Anthony R. Fiorillo and Ronald S. Tykoski (2014) named Nanuqsaurus hoglundi from the Iñupiaq nanuq, meaning "polar bear", and the Greek sauros, meaning "lizard". The epithet is after Forrest Hoglund, for his philanthropical and cultural institutions work.

## Description

*Nanuqsaurus* DMNH 21461 was estimated at 5-6 meters (16-20 feet) long at naming, half the length of *Tyrannosaurus*. It was estimated at 500-900 kilograms (1100-2000 pounds). This small size was postulated to be an adaptation of its northern environment. However, later studies found its size is unfounded, and was likely similar in size to other North American tyrannosaurids, like *Albertosaurus*, based on undescribed adult teeth and postcrania. A ridge on the skull shows it was related to *Tyrannosaurus*. The reconstructed skull is 60-70 centimeters (24-28 inches) long. As a tyrannosaurine, it is diagnosed as a thin, rostrally forked and median spur on the fused parietals, who overlap and separates the frontals within the sagittal crest, frontals with a long and rostrally-pointed process that separates from the prefrontal and lacrimal facets and the first 2 dentary teeth are smaller than the teeth to their posterior. Some estimates state it is 7 meters long, comparable to a juvenile *Tarbosaurus*.

K461-V-001, AK383-V- 172, AK383-V-175, AK491-V-089, AK300-V-086, AK298-V-031, AK390-V-034, AK390-V-041 and AK455-V-001 are all indeterminate tyrannosaurid teeth from Prince Creek. 2 of these have a basal D-shaped cross section with no anterior and posterior carinae. The denticles are similar in shape to *Dromaeosaurus*, with a diagnostic blood groove between the denticles identifying the remains as non-dromaeosaurid. It was suggested these tyrannosaurids were endemic and not migrants from another region, and the teeth are very similar to other tyrannosaurid taxa. These are all from Kikak-Tegoseak Quarry, Liscomb Quarry and Byers Bed. Tykoski has somewhat confidently referred all of these to Nanuqsaurus. Some teeth have further been identified as part of larger individuals.

Undescribed material includes a fragmented rib, a dorsal vertebra, a caudal vertebrae, a quadrate, and various teeth. These were first unveiled by Erickson et al. (2021) and Patrick Druckenmiller in a Youtube video for the Alaska Paleo-Project. In the video he states more material is being searched for and described. The material within the video is compared to a juvenile *Tarbosaurus*, which estimates this material to 7 meters in length.

## Classification

G.S. Paul in the Princeton Field Guide to Dinosaurs (2010) finds it to be a dwarf of too few remains to declare a new species, yet states that it may be a part of *Tyrannosaurus* and a competitor with *Troodon*. These conclusions are not supported elsewhere. *Nanuqsaurus* is a highly-derived tyrannosaurine, sister to a clade comprised of *Zhuchengtyrannus*, *Tarbosaurus* and *Tyrannosaurus*:

## Paleobiology

*Nanuqsaurus* lived on northern Laramidia, which experienced fairly temperate weather but dealing with daylight changes through the year, having seasons where food was not widely available. Prey increased during the summer and declined in the winter. Fiorillo and Tyloski first suggested this food shortage may explain how small *Nanuqsaurus* was first estimated to be, but studies come to show that *Nanuqsaurus* having a larger size than what was expected would suggest that food were more accessible than previously agreed upon, especially with warmer climates as opposed to polar climates . A trackway was discovered on a steep cliffside at Denali National Park.

## Paleoecology

The holotype specimen assigned to *Nanuqsaurus* comes from the Maastrichtian age Prince Creek Formation. At an age of 71–68 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 animals in the Prince Creek formation region during the Lancian faunal stage. The climate of Prince Creek 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, the hadrosaurid *Edmontosaurus* (similar to *E. regalis*), 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 referred to the dubious genus *Troodon,* the dromaeosaurid *Dromaeosaurus*, the dromaeosaurid *Richardoestesia* (similar to *R. isosceles*), an unnamed saurornitholestine, an unnamed ornithomimosaur, and multiple avialans. Some of these animals fell prey to *Nanuqsaurus*, with it being the apex predator of the ecosystem. Many of theropods located in Prince Creek are of smaller stature.

## Gallery

Teeth from Kikak-Tegoseak Quarry referred to *Nanuqsaurus*.
**Credit: Ron Tykoski.**Teeth from Kikak-Tegoseak Quarry referred to *Nanuqsaurus*.
**Credit: Ron Tykoski.**Teeth from Kikak-Tegoseak Quarry referred to *Nanuqsaurus*.
**Credit: Ron Tykoski.**
## References

1. ↑ 1.0 1.1 https://www.cell.com/current-biology/fulltext/S0960-9822(21)00739-9?utm\_source=EA
2. ↑ 2.0 2.1 https://en.wikipedia.org/wiki/Nanuqsaurus
3. ↑ https://www.tandfonline.com/doi/abs/10.1671/0272-4634%282000%29020%5B0675%3ATTFTPC%5D2.0.CO%3B2
4. ↑ https://twitter.com/Paleo\_Tykoski/status/1377984423824658432
5. ↑ 5.0 5.1 https://www.youtube.com/watch?v=4tScqOtjVGE&ab\_channel=JamesHavens
6. ↑ https://press.princeton.edu/books/hardcover/9780691167664/the-princeton-field-guide-to-dinosaurs
7. ↑ https://www.pbs.org/video/alaskan-dinosaurs-olozit/