A 70 million year old fossil found in the Late Cretaceous sediments¹ of Alaska reveals a new small tyrannosaur（霸王龙）, according to a paper published in the open-access journal PLOS ONE on March 12, 2014 by co-authors Anthony Fiorillo and Ronald S. Tykoski from Perot Museum of Nature and Science, Texas, and colleagues. Tyrannosaurs, the lineage of carnivorous theropod ("beast feet") dinosaurs³ that include T. rex, have captivated our attention, but the majority of our knowledge about this group comes from fossils from low- to mid-latitudes⁴ of North America and Asia. In this study, scientists analyzed⁵ the partial skull⁶ roof, maxilla（上颌骨）, and jaw⁷, recovered from Prince Creek⁸ Formation in Northern Alaska, of a dinosaur² originally believed to belong to a different species, and then compared the fossils to known tyrannosaurine species.

 

According to the results of the authors' analysis, the cranial bones represent Nanuqsaurus hoglundi, a new tyrannosaurine species closely related to two other tyrannosaurides, Tarbosaurus and Tyrannosaurus. This new dinosaur is estimated to be relatively⁹ small, with an adult skull length estimated at 25 inches, compared to 60 inches for T. rex. The new species likely inhabited a seasonally¹⁰ extreme, high-latitude continental¹¹ environment on the northernmost edge of Cretaceous North America.

 

The authors suggest that the smaller body size of N. hoglundi compared to most tyrannosaurids from lower latitudes may reflect an adaptation to variability in resources in the arctic seasons. Further diversification¹² may stem from the dinosaurs' partial isolation¹³ in the north by land barriers, such as the east-west running Brooks¹⁴ Range. Although the preserved elements of N. hoglundi are fragments, the authors point to morphological（形态学的） data to provide support for its place among derived¹⁵ tyrannosaurines. This discovery may provide new insights into the adaptability¹⁶ and evolution of tyrannosaurs in a different environment, the Arctic.

 

"The 'pygmy（矮小的） tyrannosaur' alone is really cool because it tells us something about what the environment was like in the ancient Arctic," said Fiorillo. "But what makes this discovery even more exciting is that Nanuqsaurus hoglundi also tells us about the biological richness of the ancient polar world during a time when the Earth was very warm compared to today."

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