As soon as you give it leave the whole building go back inside talk to the guy who took the fossil to receive your very own Lileep(root fossil) or Anorith(claw fossil).
go outside of the whole devon co. and go back to the guy you gave the fossil (make sure you have a space for your fossil pokemon) and he'll give you a pokemon.
All you have to do is leave the bulding then imediatly return. leaving the building triggers it to finish. so the time depends on you.
Make sure you have put the fossil in you bag. Press Y and select treasures select the fossil and select put into bag. Then you will be able to exchange it for a Pokemon.
When in the desert, search for the fossils. when you find them, choose the "Root fossil", NOT the "Claw fossil". then go to the Devon corp. building in rustboro city. In the second floor, talk to the guy to the lower right. then answer "yes" on his question. go leave the building, make room for an extra Pokemon, and go back to the guy in the building. he will give you a lvl. 20 Lileep. Train him to lvl. 40, and he will evolve into Cradily.
take it to the pewter museum and talk to the guy with the black hair he will take your fossil and make it into an omanyte
go outside of the whole devon co. and go back to the guy you gave the fossil (make sure you have a space for your fossil pokemon) and he'll give you a pokemon.
Go to Rustboro and then to the Devon Center. Go to the second floor, and talk to the scientists working there. One of them will offer to transform your fossil into a pokemon.
go to devon corp, on the second floor on the bottom right, there is a guy that is working on a machine that can regenerate pokemon fossils, which he says is working. he will take ur fossil, and turn it into a pokemon.
If I remember right you go to the DEVON CORP. and go to the 2nd floor. Talk to the scientist at the bottom of your gameboy screen. ( i know you will see him) He'll tell you his success in turnin' fossils into pokemon.
In Pokemon Sapphire, Ruby, and Emerald you enter the Devon Cooperation in Rustboro City on the second floor. From there, talk to the professor that says that he is trying to resurrect Pokemon from fossils. If you have the Claw or Root Fossil, (Find in the desert) he will say that he wants to try to bring the fossil back to life. Say yes, and exit the room. Make room in your Pokemon Party and come back. He will say that it is done. If you gave him a Claw Fossil, you will have a Level 20 Anorith. If you gave him a Root Fossil, you will have a Level 20 Lileep.
In Devon Corp.
You make a Pokemon hold a root fossil on another game. Then you migrate or trade that Pokemon to the game that you have the claw fossil.
The museum in Oreburgh city has a guy behind the counter that will make you a Pokemon from a fossil.
You can not catch Lileep in Sapphire or Ruby. You find two fossils in the Desert and one of them is Lileep. To make the fossil Lileep, go to RustBoro city and go the Devon Cooporation. On the second floor, there is a scientist at the bottom who will turn fossils into Pokemon.
take it to pewter museum
All you have to do is leave the bulding then imediatly return. leaving the building triggers it to finish. so the time depends on you.
you get a fossil on make it come back to live