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Geologist Bill Simpson cleans Sue, a 67-million-year-old Tyrannosaurus Rex on display at the Field Museum on November 12, 2013 in Chicago, Illinois. Sue is the largest, most complete, and best preserved T. Rex ever discovered. Simpson carefully cleans the skeleton twice a year.
As if one single tyrannosaurus rex weren't menacing enough, there's now evidence that these massive carnivores might have hung out in posses. Here to tell us more is Brian Switek, who writes about all things dino for National Geographic.