underground, they are rare.
in eterna city
revive old amber obtained by mining in underground or trade
In Pokemon Diamond there is a location known as the Amber Castle. To get there, you need to first go to the Eterna Forest.
Aerodactyl comes from the old amber you need to revive it on seafoam islands on Pokemon leaf green and fire red , the coal museum in oreburgh on diamond and pearl. hope this helps!
Armour,Skull,Helix,Dome,Old Amber and Root Fossils.
You need to go in the underground and find an Old amber or trade it with someone.
You find a old amber underground (really rare) and get the guy at the mining museum to turn it into a pokemon.
You need to get an old amber under ground but you need to search very very carfully 100%
The Pokemon Aerodactyl can be obtained from the Old Amber. You can find the Old Amber from the Underground. Take it to the Mining Museum in Oreburgh City to obtain Aerodactyl.
It's only in the shows
One must go underground and mine for it. In my game, it took a little bit to find (with out cheats)
Helix Fossil - Omanyte Dome Fossil - Kabuto Old Amber - Aerodactyl Root Fossil - Lileep Claw Fossil - Anorith Skull Fossil - Cranidos Armor Fossil - Shieldon -------------------------------------------