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Illustration of the pygmy tyrannosaur.

An artist's rendering shows N. hoglundi below Alaska's northern lights.

ILLUSTRATION BY KAREN CARR

Christine Dell'Amore

National Geographic

Published March 13, 2014

A great discovery came in a small package for paleontologists who've unearthed a new species of tiny tyrannosaur in northern Alaska.

Dubbed Nanuqsaurus hoglundi, the polar pygmy measured about 20 feet (6 meters) long, about half the size of its close relative Tyrannosaurus rex. The first part of the dinosaur's name, Nanuq, means "polar bear" in the Alaska Inupiat language, a nod to the tyrannosaur's role as top predator in its late Cretaceous environment. Hoglundi honors philanthropist Forrest Hoglund, according to a new study, which appeared March 12 in the journal PLOS ONE.

Paleontologists nearly overlooked N. hoglundi as they searched for a type of horned dinosaur in the Prince Creek formation in 2006. While removing 70-million-year-old rocks from a hole, paleontologist Tony Fiorillo noticed unusual bones that looked like skull fragments. At the time, though, "we had bigger fish to fry, and we put it aside," he said, but "some things stick in your mind." Later at his lab, Fiorillo realized that indeed he'd found pieces of the top of the skull and jaw of a new tyrannosaur. (Also see "Tiny T. Rex Found—150-Pound Species Came First.")

Silhouettes showing approximate sizes of representative theropods.
The new tyrannosaur, N. hoglundi (A), is shown in comparison to other tyrannosaur species (B to E), as well as two birdlike dinosaurs from the same time period.
Illustration courtesy Anthony R. Fiorillo, Ph.D. and Ronald S. Tykoski, Ph.D.

What's more, a particularly shaped ridge on its head, among other similarities, indicated the carnivore was a close cousin of T. rex—"not some second cousin twice removed kind of deal," quipped Fiorillo, of the Perot Museum of Nature and Science in Dallas.

Why So Small?

Though T. rex is undoubtedly the "all-star center fielder for the New York Yankees in the dinosaur world," Fiorillo said, there are actually many species of tyrannosaur that lived in Asia and North America during the Cretaceous.

In N. hoglundi's day, northern Alaska—then part of an ancient subcontinent called Larimidia—had weather like modern-day Seattle: seasonally cold but not frigid. The dinosaur likely would have wandered in the valleys beneath majestic snow-capped peaks and hunted other dinosaurs, including a duck-billed species, amid towering sequoias and flower-studded coastal plains, said Fiorillo, who received funding from the National Geographic Society/Waitt Grants Program. (Quiz: Test your dinosaur IQ.)

Unlike Seattle, though, the Arctic was still a rough place, with long periods of darkness and light, as well as distinct seasons in which food wasn't readily available. For instance, prey species likely would have exploded in number during the summer, but then fallen off in the dark winter, leaving predators with little to eat.

This lack of food may explain N. hoglundi's diminutive size, since a large animal can't survive on scarce resources, explained Fiorillo. (Watch video: "Dinosaurs 101.")

But that's puzzling, since a general rule of biology is that many animals get bigger at the Poles—the polar bear, for instance, is the largest bear species, noted paleontologist Matt Lamanna, of the Carnegie Museum of Natural History in Pittsburgh. The reason may be that big animals lose heat more slowly than smaller animals do.

"It's a pretty surprising discovery," said Lamanna, who wasn't involved in the new study. "In the modern world you tend to find big stuff at the Poles, and it's interesting that in the Cretaceous world that may not hold true."

Fuzzy Polar Dweller?

Also unknown is the behavior of the newfound dinosaur, though there are a few clues. For instance, the shape of its skull suggests it had an inflated area of its brain devoted to smell, which suggests the animal—like T. rex—relied heavily on scent to hunt its prey.

Also, it's possible that N. hoglundi was covered in fuzz, like other tyrannosaurs. And, Lamanna said, if you consider a "probably warm-blooded creature living at the top of the world, it would stand to reason that maybe [the coat] was a little thicker than relatives farther south." (Related: "One-Ton Feathered Dinosaur Found: Fluffy and Fierce.")

Despite these mysteries, one thing that's brought N. hoglundi to life is the grooves the predator left gnawing on the bones of its prey, which were also found at the Prince Creek site, all those millions of years ago.

"By seeing tooth marks, it makes them the animals that they really were," Fiorillo said, "instead of just a cool collection of objects."

Follow Christine Dell'Amore on Twitter and Google .

17 comments
Katrina Lisa
Katrina Lisa

Maybe Mini Rex couldn't grow any bigger in the Arctic cold because it's a reptile? First thing I thought of anyway although I don't have the scientific know-how to explain my logic. Also, was the Arctic at the time as cold as it was today?

Ivan Lau
Ivan Lau

I thought T Rex was only one specie in the past.

Krzysztof Wasilewski
Krzysztof Wasilewski

I think that during a sort of harsher winter that Alaska's T-rex migrated down to the south following other species that did it routinely.

Tamar Nadell
Tamar Nadell

Cool but the picture looks kind of fake. Overall its pretty good.

Craig Nordmark
Craig Nordmark

Seems that the idea that polar animals are bigger than their southern counterparts is true only up to a point. At some point the size advantage for retaining body heat is overcome by the need to be able to survive when prey is scarce or small. This dino is "small" compared to T-rex but huge compared to a polar bear. 

Polar bears can hibernate in the coldest/darkest parts of the year when prey gets scarce. The Cretaceous climate was not polar by todays standards (though we are warming up) so some food would always be available. However, I believe there isevidence that many of the polar herbivorous dinos migrated. This would leave only small prey.


Ken Black
Ken Black

I could be wrong, but I would think being larger in a cooler climate would suit warm-blooded animals well for some of the reasons in the article. However, the opposite would be true for cold-blooded animals such as dinosaurs. Hence, the size of the latest discovery.

Pam Evans
Pam Evans

I don't know much about anything, but it seems odd that sequoias were mentioned as being in Alaska eons ago; I thought they were native to California?

craig hill
craig hill

The Kodiak bear is larger than a polar bear. C'mon, Nat G.

Clark Thomas
Clark Thomas

Some pygmy!...  An adult could dine on adult polar bears. 

Ted Albalos
Ted Albalos

If they were still around, I wonder if the SPCA would accept them when owners decided they were too costly to feed (Not to mention the neighbors complaining about their missing german shepherds, rottweilers and children). 

Brad Hawthorne
Brad Hawthorne

Dumb question, but how do they know it's not just a juvenile T Rex?

Craig Nordmark
Craig Nordmark

@Ken Black I believe most dinosaurs, especially therapods, have been shown to be warm blooded. Most dinos were homeothermic to some degree, helping in their dominance of their cold-blooded forebearers.

Christine Dell'Amore
Christine Dell'Amore

@Pam Evans  There is evidence of them living there, so they must have ranged farther north when the climate was milder in Alaska! Thanks for your comment. 

Christine Dell'Amore
Christine Dell'Amore

@craig hill  Thanks for your comment. According to bear expert Steven Amstrup: "When you look over their whole range, polar bears are on average bigger than brown bears.  Brown/grizzly bears vary significantly in size with some being about the size of black bears and others being enormous.  Polar bears on the other hand have less size variation across their range.  


The largest of the brown bears that live on Kodiak Island, the Alaska Penninsula, and Kamchatka are as large as the largest of polar bears.  Elsewhere, brown bears are generally smaller." 

Andrew Booth
Andrew Booth

@Brad Hawthorne In most vertebrates bones and joints change over the course of an individual's life. I presume it's just as easy for paleontologists to determine that a fossil bone or joint is from a young skeleton or an adult as it is for anatomists with modern bones. The skeleton of this new tyrannosaur has obviously been determined as being that of an adult, even though it's much smaller than other tyrannosaurs.   

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