Do i need WotLK to play the WoW PTR?

I wana know if I need the WotLK expansion to play a lv 80 on the PTR I have BC and I wana try a lv 80 and a flying mount and stuff I know flying mounts r only 60 but my hghes guy is only a 28 also i no that on PTR premades you get alot of gold and gear i wana try out and i really want a dk plz tell me wat i need to do