High above the Arctic Circle, a tiny beast once stalked the polar realms—a diminutive Tyrannosaur adapted for life in the north. Roughly 70 million years ago Nanuqsaurus hoglund, whose name means “polar bear lizard,” roamed the Alaskan terrain, unknown to the world until 2006, when paleontologist Anthony Fiorillo dug up some skull and jaw fragments. Based on new analyses of those old fossils, Fiorillo and colleague Ronald Tykoski showed in a new study that the mini-tyrannosaur was definitely a distinct species, a pint-sized carnivore who wandered the northern lands.
The Arctic tyrannosaur Nanuqsaurus hoglund measured 23 feet from tip to tail, says Alexandra Witze for Nature. That's a little bit less than 60 percent of the length of the larger Tyrannosaurus Rex, to which the polar bear lizard is related. On the scale of all non-avian dinosaurs ever, though, this is still pretty big.
But Nanuqsaurus hoglundi was not just a baby version of a bigger beast. Witze reports: “The Nanuqsaurus fossils must come from a fully grown dinosaur, says Fiorillo, because one jaw section shows a distinctive peg-and-socket pattern that is found only in adult animals.” The Guardian:
"It wasn't until the past few years, with more work being done on growth rates, that we were able to look at these pieces in finer detail and realise that they weren't a youngster of a known species, but a mature individual of something new," Tykoski told the Guardian. "It is absolutely a pygmy tyrannosaur."
And, lest you think this Arctic tyrant was actually living further south, and the Earth's tectonic plates have just shifter poleward with time, Ron Blakey's paleogeographic maps show that Alaska was definitely still well above the Arctic Circle 70 million years ago.
So what made Nanuqsaurus so petite? “The study authors believe that Nanuqsaurus hoglundi developed a smaller body than other tyrannosaurs because the seasonal changes in light in their Arctic home put greater constraints on their food supply, limit[ing] just how big they could get,” says io9.