From Bulbapedia, the community-driven Pokémon encyclopedia.
The Old Amber (Japanese: ひみつのコハク Secret Amber) is a fossil which can be regenerated into Aerodactyl.
The Old Amber is different than the other fossils, being a type of fossilized substance rather than a fossil named by its appearance; however, the Aerodactyl skeleton in Pewter City Museum implies that it does have its own fossilized remains.
In the games
In the Generation I and III games, Old Amber is a key item obtained in a back room of the Pewter Museum of Science, from one of the scientists, who believes that it could be resurrected. Cut is required too access the room, as it is blocked by a cuttable tree. It is given to the player by one of the scientists working there. If brought to the Pokémon Lab on Cinnabar Island, Old Amber can be regenerated into an Aerodactyl.
In Diamond, Pearl, and Platinum, it is no longer a key item, being demoted to simply an item. It can be found by mining in the Underground after obtaining the National Pokédex. If brought to the Oreburgh Mining Museum, Old Amber can be regenerated into an Aerodactyl.
In HeartGold and SoulSilver, Old Amber can be found randomly by smashing rocks at the Ruins of Alph. If brought to the Pewter Museum of Science, Old Amber can be regenerated into an Aerodactyl.
In Black and White, a Worker in the Ice Rock room of Twist Mountain hands out a random fossil from previous generations, including Old Amber, once per day. If brought to the Nacrene Museum, Old Amber can be regenerated into an Aerodactyl.
In the anime
In the anime, Gary Oak obtains an Old Amber and uses it to revive an Aerodactyl in Putting the Air Back in Aerodactyl.
In the manga
In the Pokémon Adventures manga
As in the games, in Pokémon Adventures, Red was able to revive an Aerodactyl from the Old Amber in the Cinnabar laboratory and added it to his team.
In the TCG
Old Amber was introduced into the TCG in Majestic Dawn. Prior to its introduction, Aerodactyl must be evolved from the Mysterious Fossil card.