I always thought the rock typing was a side-effect from the fossil reviving process.Since fossilization is the replacement of stuff with rock, and you’re specifically reviving from FOSSILS not DNA (except, I guess, for aerodactly) the typing changed
Mostly works for the games (except for, as you mention, Aerodactyl). Doesn’t work once you bring the anime into it, because there are episodes where Ash encounters surviving populations of supposedly extinct Pokémon (like the Kabuto in the Orange Islands), and even one where he actually travels through time and sees Tirtouga and Carracosta in their natural prehistoric habitat. It’s pretty clear from instances like these that the fossil Pokémon aren’t substantially altered from their original biology.
Pokémaniacal 