To get fossil Pokemon GO to the Nacreen Museum and talk to the people right inside the door. One of them takes you fossils and turns them back into pokemon.
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The lock capsule is currently useless (and unable to open), but is speculated to be of some use in Pokemon Black and White.
You have to get the the National Dex (beat the Elite Four) before you can go into the Fossil Maniac's cave.
I don't think you can, in emerald you need the nationaldex and POW! it's open but in ruby and sapphire you can't.
in the city pewter museum you talk to the professor in the right (you need fossil and and open slot in your party). by the way i have Pokemon heart gold, good game!!!!
If you go to Oreburgh City, in the fossil museum, the guy on the right hand side of the counter will revive any fossil. Give it to him, walk outside, come right back in, he'll say you took a long time and then he'll give you your Pokemon if you have a spot open in your party.