[The Lone Ranger]

In all likelihood, most dinosaurs were feathered to at least some extent, particularly the smaller species. The bigger ones may have had some quills (perhaps for display purposes), but most probably weren't covered in feathers. For the same reasons that modern elephants don't need to be covered in fur -- they were plenty big-enough that their sheer body mass would have acted as insulation.

That having been said, there were plenty of dinosaur species living in what's today Antarctica, and also in regions that were north of the Arctic Circle at the time. Antarctica wasn't as far South as it is today, but there were plenty of dinosaur species that lived in regions that would have been quite cold during the Winters. That is, there were plenty of dinosaurs living in Arctic and Antarctic regions, dinosaurs who would have experienced long, snowy Winters and weeks or months at a time where there was little or no sunlight. As such, it's not at all unlikely that there were some species of large, feather-covered dinosaurs, just as there were Wooly Rhinos and Wooly Mammoths during the last Ice Age.