Paleontologists have discovered a new diminutive tyrannosaur that hunted prey in the ancient arctic lands of northern Alaska. This is the first tyrannosaur discovered in a polar region, and it’s already reshaping our understanding of Cretaceous Arctic ecology.
The 70-million-year-old fossils belong to the new genus and species Nanuqsaurus hoglundi, named after “nanuq” the Iñupiaq word for polar bear.
The majority of what we know about tyrannosaurs -- the lineage of carnivorous “beast-footed” theropods that include T. rex -- come from fossils unearthed in the low- to mid-latitudes of North America and Asia. The partial skull roof, maxilla, and jaw described here were found in the high latitudes of the Prince Creek Formation on Alaska’s North Slope.
Those cranial bones, dug up in 2006, were originally believed to be from a different species, one that’s known from other parts of the world. But then Anthony Fiorillo and Ronald Tykoski from Perot Museum of Nature and Science in Dallas compared the fossils to known tyrannosaurine species. “Only in the last year or so, after some other tyrannosaur papers came out, we were able to plug these fragments into those analyses -- and a little light bulb went on over our heads,” Tykoski tells Nature. “We said, holy smokes, this thing really is different.”
This new dinosaur is relatively small, with an adult skull length estimated at 25 inches (A, pictured), compared to 60 inches for T. rex (B,C). Based on skull proportions, the Alaskan dino was probably just over half the length of the King of Tyrants. And according to Fiorillo, the fossil couldn’t have come from a baby T. rex because the jaw fragment bears of the peg-and-socket pattern only found in adults.
Their smaller body size compared to most tyrannosaurids from lower latitudes may reflect adaptations to the seasonal extremes of polar living. While the northernmost edge of Late Cretaceous North America was warmer than today, the diminutive dino would still have to adapt to all the variability in resources that comes with arctic seasons. “There was something about that environment that selected for tyrannosaurs developing a smaller body size,” Fiorillo tells Nature. Despite how living six months in light and six months in dark affected food availability, these dinosaurs were active hunters -- not scavengers. Though, their relatively small size may reflect those ecological pressures.
“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,” Fiorillo says in a press release.
The work was published in PLOS One this week.
Images: Nanuqsaurus hoglundi illustration by Karen Carr (top) & relative size of N. hoglundi in 2014 Fiorillo, Tykoski via Creative Commons (bottom)