Pokemon diamond how do you get an Aerodactyl?

first you have to go underground. then you keep "treasure-hunting" until you find an item called: Old Amber. (you need the national pokedex) then go to oreburgh city, go to the museum, talk to the guy in the scientist lab coat , talk to him and then go out. go back in, and talk to him again, he will give you Aerodactyl. written by :L perry