Arctic’s Tyrannosaur Was a Tiny Terror

Tyrannosaurs included some of the largest carnivores of all time, but a new Arctic tyrant was a pipsqueak compared to T. rex.

Near the end of the Cretaceous, about 70 million years ago, tyrannosaurs were North America’s apex predators. From Teratophoneus in the south to Albertosaurus in the North, these deep-skulled, tiny-armed theropods were the most menacing dinosaurs of their time.

But not all of these Late Cretaceous predators were giants.

In a study published Wednesday in PLoS One, paleontologists Anthony Fiorillo and Ronald Tykoski of Dallas, Texas’ Perot Museum of Nature and Science have named a diminutive tyrannosaur that once trod beneath the Arctic’s northern lights.

The researchers have dubbed the dinosaur Nanuqsaurus hoglundi – a title combining the Iñupiaq word for polar bear with a species name honoring geologically-minded philanthropist Forrest Hoglund.

Bones of the tyrannosaur were recovered at the Kikak-Tegoseak Quarry on Alaska’s North Slope. Even with continental shifts since the Cretaceous, the site would have been within the Arctic Circle during the heyday of Nanuqsaurus.

A hypothetical reconstruction of Nanuqsaurus showing the placement of skull bones. From Fiorillo and Tykoski, 2014.
A hypothetical reconstruction of Nanuqsaurus showing the placement of skull bones. From Fiorillo and Tykoski, 2014.

Relatively little of the dinosaur has been found so far. The material Fiorillo and Tykoski drew upon to name the dinosaur consists of disarticulated skull bones, including parts of the skull roof and the jaws. Some of these bones were previously thought to belong to the classic tyrannosaurs Albertosaurus and Gorgosaurus, but the new analysis by Fiorillo and Tykoski found that the North Slope fossils differ in the arrangement of the bones on the skull roof and the size of the tooth sockets. And since some of the skull bones are fused, this Nanuqsaurus was likely at or approaching adult size.

Size matters, in this case, because the most immediately striking aspect of Nanuqsaurus is the tyrannosaur’s small size. Using other tyrannosaur skulls as a guide, Fiorillo and Tykoski hypothesize that the skull of a mature Nanuqsaurus was not much more than two feet long. The skull of the largest known T. rex – the biggest known tyrannosaurs – were about five feet long. Likewise, at an estimated 25 feet long, Nanuqsaurus could have stood in the shadow of a 40-foot-long T. rex.

Still, despite the size difference, T. rex and Nanuqsaurus were relatively close relatives.

A phylogeny of North America’s Late Cretaceous tyrannosaurs. From Fiorillo and Tykoski, 2014.
A phylogeny showing the relationship of Nanuqsaurus to other Late Cretaceous tyrannosaurs in North America. From Fiorillo and Tykoski, 2014.

As hypothesized by Fiorillo and Tykoski, Nanuqsaurus shares the pedigree of the most famous tyrannosaurs. The new dinosaur’s bones are more similar to the last of the tyrannosaurs, including Tarbosaurus from Mongolia and T. rex from North America, than to the sleeker, more gracile tyrannosaurs Albertosaurus and Gorgosaurus that lived at the same time.

Defining Nanuqsaurus as a unique species closely related to T. rex adds another data point to the bigger picture of how tyrannosaurs evolved and spread around the northern hemisphere during the Cretaceous.

Based on previous discoveries, including the recently-described tyrannosaurs Teratophoneus and Lythronax, paleontologists have suspected that there were mountain ranges and other geographic barriers that caused tyrannosaurs to evolve into different species in pockets of isolation. Nanuqsaurus further fits this pattern of distinct tyrannosaurs evolving along the latitudes.

The small stature of Nanuqsaurus could be a clue to such a barrier that caused the dinosaur to evolve in unique conditions. Given the harsh seasonal swings between months of darkness and light in its ancient habitat, Fiorillo and Tykoski propose, Nanuqsaurus may have evolved to be more compact to better survive on scarce resources during the long nights of the Cretaceous Arctic.

And, of course, this means that March of the Dinosaurs and Walking With Dinosaurs 3D have some revisions to make. Instead of being a towering monster, Alaska’s tyrannosaur was a modestly-sized carnivore that would have best avoided tussling with the burly herbivores of its time. Future films set the in the Cretaceous Arctic will have to find a new villain.

[Full disclosure: Part of the study funding was provided by the National Geographic Society/Waitt Grants Program.]


Fiorillo, A., Tykoski, R. 2014. A diminutive new tyrannosaur from the top of the world. PLoS ONE. 9, 3: e91287. doi:10.1371/journal.pone.0091287

8 thoughts on “Arctic’s Tyrannosaur Was a Tiny Terror

  1. Wow! This news is astonishing! Finally a new species of tyrannosaur from the Arctic is described and named. Since I watched March of the Dinosaurs and, of course, Walking with Dinosaurs the 3D movie, I really thought that especially Albertosaurus were the only “tyrants” which lived further north close to the Arctic Circle but not beyond or inside it. Now we learned that Nanuqsaurus hoglundi did! I’ll be rooting for Firorillo and his team to discover more specimens and missing parts of the Arctic dinosaurs species from the Late Cretaceous! I love the “tyrant lizards”!

  2. I have a feeling this material will be considered nondiagnostic in the future. It is beyond scrappy, and I feel like Fiorillo & Tykoski are really reaching for diagnostic features.

    The real issue is that the tunnel that was blasted into the Colville River slope only lasted two or three dig seasons before it was closed because it became a safety hazard. AFAIK, only two or three blocks of rock were yanked out before the closure. There could be more of “Nanuqsaurus in those blocks,” but it’s unlikely.

    Another irritation is that Alaska’s dinosaurs (P. perotorum, now “Nanuqsaurus”) are being housed in the Perot Museum of Nature & Science, in Dallas, Texas. I understand that’s where Fiorillo & Tykonski work, but I feel like Alaska’s dinosaurs should stay in Alaska–at least send us some high-quality replicas. I know of three museums that would adequately–and happily–house our state’s fossil heritage.

  3. You are telling me a Tyrannosaurus lived in darkness several months of the year? The thought had never crossed my mind.

  4. Not much material to base a description of a new taxa. I suspect that the validity of this taxon will be questioned in the future.

  5. Yes, it is a little disconcerting at how scrappy it is. Who knows, maybe someday they can reopen the mine when technology allows it.

    @ Zach Miller:
    I feel ya. I think fossils ought to stay in their homeland (or at least have good representation there). It’s the same story here on the Central Coast: most of the fossils have left the region. I have counted over 4500 vertebrate fossils that are housed in foreign institutions (so far; not all museums have online databases, and not all of them have good online databases. The Los Angeles Museum doesn’t have one, so i haven’t been able to get an exact number. But i know they have a lot.). Repatriation of fossils is never going to happen, so unfortunately casts are the best we can hope for. Just one of the sad realities of paleontology.

  6. If anybody was curious about the precise age, this specimen is 70-69 million years old which puts it in the earliest part of the Maastrichtian stage. What a brilliant beastie! Hope the authors return to find more specimens.

Leave a Reply to Aidan Cancel reply

Your email address will not be published. Required fields are marked *