NOTE: I keep seeing them referred to as “dire wolves”, even in scholarly sources like this linked article. But it bugs me. “Dire wolves” means wolves that are dire. This is an accurate description, as far as that goes, but it isn’t grammatically correct, not if the term is meant to designate a separate species than plain old ordinary wolves—which it is. Thus they are “direwolves” on this site and shall remain such.
As far as them *being* a whole different kind of animal, they were. They weren’t just bigger versions of the wolves we have today, this new study suggests. They didn’t look like the direwolves on GAME OF THRONES. Nor did they like the cold. In fact this inability to adapt to the cold might be the reason for their extinction.
Said zooarchaeologist Angela Perri: “I certainly don’t think the average dire wolf [sic] would have been excited about living in frozen Winterfell…I suspect [the direwolves from GAME OF THRONES] would look more like one of the more warm-adapted canids, such as dholes [a shorthaired wild dog species from Asia]…Dire wolves [sic] just didn’t have the ability to adapt, apparently.”
And they were so distinct from today’s wolves that the two species didn’t interbreed. Liked to keep to themselves, those direwolves did.

I was honestly hoping for a little more information but since they went extinct a long time ago and there isn’t a lot of info on them this was pretty helpful