"No less intriguing are the known ranges of some late dinosaurs. The British geologist Stephen Drury notes that forests within 10 degrees latitude of the North Pole were home to great beasts, including Tyannosaurus rex. 'That is bizarre,' he writes, 'for such a high latitude is continually dark for three months of the year.' Moreover, there is now evidence that these high latitudes suffered severe winters. Oxygen isotope studies suggest that the climate around Fairbanks, Alaska, was about the same in the late Cretaceous period as it is now. So what was Tyrannosaurus doing there? Either it migrated seasonally over enormous distances or it spent much of the year in snowdrifts in the dark. In Australia - which at that time was more polar in its orientation - a retreat to warmer climes wasn't possible. How dinosaurs managed to survive in such conditions can only be guessed."
And there you have it.