The pokedex says that palkia learns the move spacial rend at 46 but you get it at 48 without knowing it. dialga diesnt know roar of time at 46 either.
In my D/P's, Palkia and Dialga both knew their signature move so I don't know what you are talking about... They both learn it at LV. 40...
I am 100% sure they hed Spatial Rend and roar of time...
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