An Ultimate Guide to Nanuqsaurus: The Polar Bear Lizard

Leave a comment / / Updated on: 4th January 2024

Name Meaning“Polar Bear Lizard”Height1 to 3 meters (3 to 10 feet)
PronunciationNah-nuk-sore-usLength5 to 9 meters (16 to 30 feet)
EraMesozoicLate CretaceousWeight500 to 900 kg (1,100 to 2,000 lbs)
ClassificationDinosauria,‭ Saurischia & TheropodaLocationAlaska, USA (North America)

Nanuqsaurus Pictures

Nanuqsaurus in Dinosauria (Series) | Photo via Paleo Media

The Nanuqsaurus

Gage Beasley Prehistoric’s Nanuqsaurus Concept

Today, the Arctic Circle is synonymous with the polar bear, the massive hypercarnivore that calls the frigid terrains of the North Pole home.

But back in the Cretaceous, a different type of carnivore ruled in one of the earth’s northernmost habitats.

The Nanuqsaurus, or polar bear lizard, was a relative of the famous Tyrannosaurus rex that lived on the northern edge of North America during the Late Cretaceous period. 

The medium-sized dinosaur lived in an environment that was quite different but still considerably brutal compared to the present-day Arctic.

Scientists only found remains of this dinosaur a few years ago (2006). Only fragmentary cranial and jaw bones belonging to one individual have been identified so far.

This means we still don’t know much about this dinosaur.

This post details some of the basic information we currently have about the polar bear lizard of Cretaceous North America. 

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Physical Characteristics 

Nanuqsaurus | Photo via Prehistoric Wiki

The only species in the Nanuqsaurus genus, Nanuqsaurus hoglundi, has been identified as a relatively small cousin of the Tyrannosaurus rex.

Due to the incomplete nature of this dinosaur’s fossil, estimates of its size are based on reconstructions of the skull fossils and comparison with other dinosaurs.

Nanuqsaurus was about half the size of the Tyrannosaurus but had a similar build and general appearance as other tyrannosaurid dinosaurs.

Length estimates for this dinosaur range from about five to six meters (16–20 feet) long.

However, some experts think it was closer in size to the Albertosaurus (another related tyrannosaurid dinosaur).

If this is right, this dinosaur’s length was between eight and nine meters (26–30 feet). The specimen skull on which size estimates of this dinosaur are based was between 60 and 70 centimeters (24–28 inches) in length.

The overall weight of the Nanuqsaurus has been estimated to be between 500 and 900 kilograms (1,100–2,000 pounds).

Medium-sized theropods typically stood at about one to three meters (3–10 feet) at the hips, and this dinosaur would have been around the same size as well.

nanuqsaurus size comparison
Gage Beasley Prehistoric’s Nanuqsaurus Size Comparison

Nanuqsaurus was a bipedal dinosaur with relatively short arms in line with the general body plan of the tyrannosaurids.

The polar bear lizard had a robust build with a large head supported by a short, muscular neck.

The strong muscular feet of this dinosaur gave it a powerful, bipedal stance. Its body would have been balanced by a long, heavy tail. 

Due to the climatic conditions up north where this dinosaur lived, many scientists think Nanuqsaurus may have had insulatory feathers all over its body.

This may have been necessary to help the dinosaur survive in such a frigid environment.

However, scientists have found no direct fossil evidence of feathers in this dinosaur. ‬

The discovery of a feathered tyrannosaur called Yutyrannus that lived in China is often taken as proof that feathered dinosaurs existed.

Yutyrannus lived in a cool environment similar to the Nanuqsaurus, which is why the North American tyrannosaur is often depicted as feathered. 

Habitat and Distribution

Fossils of the Nanuqsaurus were recovered from the Prince Creek Formation located in the North Slope Borough of Alaska, United States.

This suggests that this dinosaur’s range may have included this part of the continent. Back in the Late Cretaceous, when this dinosaur was alive, the North American continent was divided into two separate land masses by the Western Interior Seaway. 

This shallow sea, which covered the central portions of North America, separated the continent into Appalachia on the east and Laramidia on the west.

The discovery of Nanuqsaurus fossils in Alaska means this dinosaur lived on the northern edge of Laramidia.

The dinosaur’s range was considerably further north compared to many of the other famous North American tyrannosaurs. 

The climate and ecology of the Arctic region were also considerably different from what we know today.

During the Cretaceous, the area where this dinosaur was found in a coastal plain between the Arctic Ocean and a mountainous area.

Arctic ocean | Explora_2005 via Getty Images

However, the area was much warmer, with coniferous forests and primitive flowering plants. 

The temperature in this region would have been similar to present-day Canada.

This suggests that the Nanuqsaurus had to experience climatic extremes different from what most of the other dinosaurs of its day endured. 

The average temperature in the Arctic region during the Late Cretaceous would have ranged from about 10 to 12°C in summer to as low as -2°C during the colder months.

The dinosaur also had to live through about 120 days of continuous low-light conditions every year.

Due to the extreme cold condition in this area, many believe this dinosaur must have had adaptations to survive the cold, such as insulatory feathers, and may have been endothermic.  

Behavior and Diet

Nanuqsaurus | NaturalBird via Dinopedia

Like other tyrannosaurids, Nanuqsaurus was a bipedal dinosaur. This means it walked on two hind legs.

The highly reduced forelimbs of dinosaurs in this group were probably only good for grasping and holding on to things.

Tyrannosaurids were generally fast and agile, which is expected for carnivorous animals that had to hunt prey. 

Determining the social behavior of the Nanuqsaurus is challenging due to the fragmentary nature of the dinosaur’s remains.

However, tyrannosaurids, like many predatory species, were largely solitary.

Occasional evidence of pack behavior exists in some species, but this has not been confirmed for the Nanuqsaurus

Based on comparison to its relatives, a predator or scavenger lifestyle has been predicted for the Nanuqsaurus.

Reconstructed skull with cast of the holotype in place, Perot Museum | Jonathan Cutrer via Flickr (CC BY-SA 2.0)

Studies of the skull specimen of this dinosaur show that it had a heightened sense of smell, probably better than that of Tyrannosaurus.‭

This is consistent for top predators that live by tracking and hunting other animals.

The sense of smell would have been particularly important for an animal living in a polar environment where things tend to get dark during certain seasons of the year. 

In addition to hunting prey, Nanuqsaurus probably relied on this sense of smell to sniff out carrion or freshly-killed prey of smaller dinosaurs like the Troodon that lived in the same ecosystem.

Experts think this dinosaur may have used its size to intimidate smaller carnivores to steal their kill. 

Going by the location of the Nanuqsaurus’ fossil, it probably lived on a seasonal diet.

With many herbivores migrating further south during the winter, Nanuqsaurus would have had seasonal prey availability.

This may have limited the dinosaur’s size compared to its relatives in warmer parts of the continent. 

Life Cycle

An artist’s illustration of Nanuqsaurus hoglundi | Photo via Dinopedia

Nanuqsaurus most likely reproduced sexually. However, the life cycle and development of this dinosaur would have been highly influenced by their environment.

For instance, since they lived in such harsh conditions, they probably mated and produced eggs towards the beginning of the warmer periods with longer daylight.

This would have been around April. The relative heat of this period would have been necessary to incubate their eggs. 

Evidence also suggests that Nanuqsaurus remained in the paleo-Arctic area all year long instead of migrating seasonally to reproduce like some animals.

This means the juveniles would have had to adjust to the harsh conditions of the region while they grew.

Like other tyrannosaurids, Nanuqsaurus juveniles probably exhibited rapid growth, developing quickly to reach maturity during their early years. 

Evolution and History

Nanuqsaurus in Dinosauria (Series) | Photo via Paleo Media

Nanuqsaurus belongs to the family Tyrannosauridae, which includes other well-known dinosaurs like Tyrannosaurus rex and Albertosaurus.

Expectedly, the polar bear lizard shares several similar characteristics with its relatives but also exhibits some unique features. 

The closest relative of the Nanuqsaurus is the Daspletosaurus, a tyrannosaurid that lived in western North America between about 77 and 75 million years ago.

Nanuqsaurus and Albertosaurus likely occupied similar positions in their respective ecosystems. 

Nanuqsaurus evolved from larger ancestors like the Albertosaurus. One notable change in morphology in this dinosaur group as they evolved is their smaller size.

Scientists estimate that this dinosaur was about half the size of the massive Tyrannosaurus rex.

The size reduction was probably an adaptation to the specific environment and ecological niche where they lived.

The smaller size of this dinosaur means it would have hunted smaller prey, such as small dinosaurs, reptiles, and even mammals within its ecosystem.

Interactions With Other Species

Northern Tyrant King | Art by James L. Havens

Although the Arctic region where this dinosaur lived experienced climatic extremes that would have made it a challenging environment to live in, Nanuqsaurus lived alongside several other dinosaur groups, including herbivores and carnivores. 

Some of the herbivores that lived alongside Nanuqsaurus include the Edmontosaurus, Pachyrhinosaurus, and Alaskacephale; a few other unnamed dinosaur groups have been identified in the area as well.

These contemporaneous large herbivores may have been restricted to the coastal lowlands and uplands of the Prince Creek landscape.

The Nanuqsaurus, on the other hand, lived in various habitats across the region and would have come in close contact with these different dinosaur groups, preying on some of them. 

A few carnivorous dinosaurs lived in this area as well. They include large-sized troodontids and the closely related Daspletosaurus.

Daspletosaurus was a carnivorous theropod dinosaur that lived in North America during the Cretaceous Period. | CoreyFord via Getty Images

These dinosaurs, especially the slightly bigger Daspletosaurus, may have preyed on juveniles or weak Nanuqsaurus individuals.

However, interactions between them may have also been in the form of competition for food and other resources. 

It’s possible that the Nanuqsaurus used its size to intimidate and steal food from the smaller troodontids, especially during periods of prey scarcity in the area.

A few other reptilian and mammalian species also lived in the area and probably formed the bulk of food for the Nanuqsaurus and other carnivores.

Cultural Significance

A Trio of Nanuqsaurus preparing to kill a stranded bull on Prehistoric Planet. | Photo via Dinopedia

Nanuqsaurus was discovered relatively recently in an area that has received limited attention in terms of paleontological research.

If there’s a lesson to be learned from this dinosaur’s discovery, it’s the fact that there is still a lot to be discovered about the Earth’s ancient past. 

The discovery of the Nanuqsaurus has contributed tremendously to our scientific understanding of the prehistoric fauna of one of Earth’s most remote regions.

Alberta and the surrounding region are famous for their dinosaur bone beds. However, the region remains largely uncharted territory for paleontological research. 

Since it is relatively new and less impressive in size, Nanuqsaurus has not achieved the same level of recognition to the general public as its larger relatives, such as Tyrannosaurus rex.

However, there are still some fascinating aspects of this dinosaur’s appearance that remain fascinating for scientists and enthusiasts.

For instance, the fact that this dinosaur was probably feathered is an interesting point of discussion that often generates interest and engagement. 


Due to its unique habitat, the Nanuqsaurus may very well be one of the most interesting members of the tyrannosaur group.

This theropod dinosaur lived in what was probably the northernmost range of dinosaurs in North America.

Surviving in an ecologically challenging landscape 75 million years ago, this medium-sized dinosaur was an apex predator that terrorized the herbivores that shared the same home range with it. 

Nanuqsaurus is known from fragmentary skull bones, a few jaw bones, and fossil tracks.

As scientists continue to research and explore the Arctic region and other parts of North America, discoveries may be made that’ll further deepen our understanding of Nanuqsaurus and its close relatives beyond what we currently know. 


How was Nanuqsaurus named?

The name “Nanuqsaurus” is derived from the native Inupiaq word “Inanuq,” which means polar bear, and the Greek word “saurus,” which means lizard.

The dinosaur’s name translates as polar bear lizard because it was discovered in Alaska—a region of North America where polar bears are native.

Was Nanuqsaurus a direct ancestor of T. rex?

A: Nanuqsaurus is not considered a direct ancestor of Tyrannosaurus rex. Rather, they are believed to be closely related members of the tyrannosaurid family.

Nanuqsaurus and T. rex likely shared a common ancestor, with Nanuqsaurus branching off earlier in the evolutionary lineage.

How was Nanuqsaurus discovered?

The fossils of the Nanuqsaurus were discovered in the Prince Creek Formation of Alaska.

Paleontologist Anthony Fiorillo discovered the partial skull of Nanuqsaurus during an expedition to Alaska in 2006. 


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