A previously unknown meat-eating dinosaur -- a petite tyrannosaur related to the much-larger Tyrannosaurus rex -- roamed Alaska's North Slope during the late Cretaceous period, scientists said on Wednesday.
The discovery was announced by paleontologists from the Perot Museum of Nature and Science in Dallas, the same scientists who have made other major dinosaur finds in Alaska's farthest-north region. The findings are detailed in a study published online in the journal PLOS ONE.
The newly identified tyrannosaur was only about 25 feet long and weighed 1,000 pounds -- a pygmy version of the much-feared T. rex, which typically measured 40 feet in length and weighed between 7 and 8 tons, the discoverers said.
The tiny North Slope tyrannosaur has been named Nanuqsaurus hoglundi. The first part of the name incorporates the Inupiaq language of the North Slope's indigenous people and roughly translates to "polar bear lizard." The second part honors Forest Oil Chairman Forrest Hoglund, a major patron of the Dallas museum and its scientific mission.
Nanuqsaurus hoglundi's diminutive size likely results from the Arctic conditions in which it lived, said discoverer Tony Fiorillo, the Perot museum's curator of earth sciences and a leader among paleontologists working in Alaska.
While the North Slope in the Cretaceous period was much warmer than it is now -- similar to the Pacific Northwest or northern Rockies -- it was, nonetheless, much colder than the lush tropical environments commonly associated with dinosaurs and ancient reptiles. And during this dinosaur's day, Alaska's North Slope was even farther north than it is now, meaning that seasonal differences in daylight were even more dramatic than they are now.
Fiorillo and research partner Ronald Tykoski, the Perot museum's fossil preparer, figure that food scarcity in the far north caused the pygmy tyrannosaur to evolve to its small size, similar to the evolution of small woolly mammoths that survived on outlying islands after most of their species had died off.
"The North Slope was, effectively, an isolated area," Fiorillo said in a telephone interview.
The specimen was definitely a mature adult, not a juvenile, he said. One of the discovered skull pieces had a pattern of jawbone sockets that existed only in mature tyrannosaurs, he said. "That's what told us we had a fully mature animal," he said. The specimen also had very small front lower teeth, a contrast to the large teeth sported by most tyrannosaurs, he said.
The specimens were found in a quarry along the bank of the Colville River, at a spot north of Umiat. It is the same site that yielded specimens of another new-to-science dinosaur species identified in 2011, Pachyrhinosaurus perotorum -- named after museum patron Ross Perot and his family -- and a juvenile member of that species, discovery of which was announced in 2013.
The dig that yielded all of these dinosaur specimens took place in 2006 and was documented by the PBS science program "NOVA". It has taken years to examine and piece together dinosaur remains packed in the in the approximately 6 tons of rock transported from Alaska's North Slope to the Dallas laboratory, museum officials said. Examination of that rock is still not yet completed, officials said.
The Colville has proven rich grounds for dinosaur discoveries, including horned and duck-billed herbavores as well as the remains of carnivores. "There were thriving populations of dinosaurs," Fiorillo said. "It was a biologically very productive area."
The discovery of so many Alaska dinosaurs -- with many of those finds by Fiorillo -- supports a theory that the prehistoric animals could survive in high latitudes because they were not entirely cold-blooded. Recent research indicates that several meat-eating theropods had feathers, presumably for warmth, he said. "That would suggest the animals would have a metabolism rate that was more like a warm-blooded metabolism than a cold-blooded," he said.
Food availability for the Arctic dinosaurs was likely limited in winter, so it is yet to be determined what they ate during that cold, dark season, he said. "We would love to know," he said. The "best we can do" for now, he said, is make parallels with what animals do today -- build up fat stores during the summer and reduce metabolism in winter, he said.
Fiorillo, who has also made important dinosaur discoveries in Denali National Park, said he cannot name a favorite among his finds.
"I love all of my children equally," he said. "This one is amazing and cool. I'm so excited by it. The Perot dinosaur was the same thing. All it tells me is there's so much potential to be had."
He is planning another Alaska expedition, to Denali, this summer.
Contact Yereth Rosen at yereth(at)alaskadispatch.com.