@frost Furry started with some fairly imaginative people - afaik they were pretty sure they were humans, but they're coming out of a lot of 60s counter cultural holdovers in the 70s and 80s, much like the first Otherkin. Sometime in the 90s you get both "furry lifestylers" - basically therians - and Otherkin, who tended to be on alt.fan.dragons or the werewolf equivalent. Neither group liked each other; the weres were sure furries just saw it as a costume, a joke, and the furries saw the lifestylers/weres as taking it too seriously (and they took it REALLY SERIOUSLY - there was a lot of "prove you're a REAL were" equivalent to making women go through all sorts of mental gymnastics to prove they're trans).

Over the last 20 years things have shifted such that if you're a therian, you've probably been around furries and are okay with that (and most furries are cool with therians).

Fursonas get a little more complex because they're an early fandom thing that came about by accident and persisted; one of the earliest furries, Ken Sample, consistently portrayed himself as a cougar, and everyone around him thought this was a great idea. And of course, where fursonas are basically roleplaying people can and do swap out (my first fursona was a wolf, would you believe it?). Nobody's ever required a fursona - and I can think of one therian who's literally never *had* a separate fursona - but it wound up accepted as a shorthand.