Nanuqsaurus

Chapter • Meet the dinosaur

Overview

Nanuqsaurus is the northernmost predatory dinosaur known to science. It is based on a handful of bones — parts of the skull roof, a maxilla and two lower jaws — from which researchers reconstructed a skull roughly 60–70 centimetres long. That makes it noticeably smaller than its famous relative Tyrannosaurus rex. The most frequently quoted body length is about six metres, though later re-examinations of the material suggest fully grown animals may have reached up to nine metres. In build it was a typical tyrannosaurid: a deep skull with thick, banana-shaped teeth, tiny two-fingered arms, long striding hind legs and a muscular tail held horizontally as a counterweight. An unusual low crest running along the top of the skull helps separate it from other tyrannosaurids. The animal lived on Alaska's North Slope at a time when the region sat even further north than it does today, well inside the polar circle. That meant months of winter darkness, midnight sun in summer, and average temperatures probably somewhere between five and ten degrees Celsius. A predator facing such extreme seasonal light shifts most likely hunted whenever prey was available, day or night, depending on the season. Many palaeontologists think Nanuqsaurus carried at least some feather covering, particularly as a juvenile, because filamentous feathers are known from other tyrannosauroids such as Yutyrannus and Dilong. No skin or feather impressions have been found for Nanuqsaurus itself, so this remains a well-supported inference rather than a fact. As the apex predator of its ecosystem, Nanuqsaurus would have hunted the plant-eaters of the Prince Creek Formation: the hadrosaur Edmontosaurus, the horned dinosaur Pachyrhinosaurus perotorum, pachycephalosaurs and small thescelosaurids. Tyrannosaurid teeth and bite marks show the group could crush bone, and Nanuqsaurus had the same robust dentition on a smaller scale. Food was probably scarcer during the dark winter months, which some researchers have suggested may explain the animal's modest size — an idea often called the resource-limited body size hypothesis, though it is still debated. The fossils were collected at the Kikak-Tegoseak quarry and nearby sites in the Prince Creek Formation. Anthony Fiorillo and Ronald Tykoski described the species in 2014 as Nanuqsaurus hoglundi. The genus name comes from the Iñupiaq word nanuq, meaning polar bear, while the species name honours the philanthropist Forrest Hoglund. The discovery mattered because it showed the polar regions supported their own distinctive predators rather than simply hosting visitors from farther south.

Chapter • Where it lived

Habitat

Nanuqsaurus lived roughly 70–68 million years ago, in the Maastrichtian, on a coastal floodplain in what is now Alaska's North Slope. The Prince Creek Formation preserves meandering rivers, seasonal flood deposits and forests of conifers and deciduous trees, with winter snow and long polar nights. Every known specimen comes from this formation, principally from the Kikak-Tegoseak quarry along the Colville River.

Chapter • Wild behavior

Behavior & Ecology

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Chapter • Scientific place

Taxonomy