You can do any, the only threads you can join on the spot without permission are threads with OPEN somewhere in their title or opening post. You can begin one yourself if you like!
I'll say though, i'm interested in rping with your character. My Archeops hasn't seen another of his evolution line that was friendly, so it'd be interesting to see how they would act together!
Problem is i'm going to be disappearing for a week starting Sunday, so if we do start a thread it's going to lack posts and progress for an entire week.