Just like in the original Pokemon games, Aerodactyl can be brought back to life if you manage to find the secret fossil hidden on the map.
This guide will help you acquire the fossil, and bring the powerful Aerodactyl back to life.
Before you can grab the Old Amber, you’ll need the Secret Technique Chop Down. You won’t receive this until reaching the end of the S.S. Anne in Vermillion City.
After getting Chop Down, head back to Pewter City and use Chop Down on the tree right behind the Museum of Science. With this tree out of the way, you can sneak into the back of the Museum where the person inside will give you the Old Amber.
Now that you’ve got the Old Amber, you’ll have to wait until you reach Cinnabar Island before resurrecting it. Upon reaching Cinnabar Island, take the Old Amber (along with the Dome or Helix fossil you chose previously), to the Pokemon Lab right next to the Pokemon Center. The man at the very back of the room next to the odd-looking machine will revive your fossil and Old Amber!