Old Amber

Fossilized resin containing DNA.

You get this in Pewter City and you can revive it into Aerodactyl. Rock/Flying with high Speed and Attack - it hits hard and outspeeds most things you'll run into. Always make sure to grab especially if you're completing the dex.

You can find Old Amber somewhere in the museum. Its a bit out of the way but if you want a physical attacker that can actually keep up with faster threats, Aerodactyl does the job!