Incorrect. For one, Spiritomb does not have any weakness's.
As for the dact. Make sure you have stone edge.
Ah, but while Spiritomb has no weaknesses, his typing also leaves him with no resistances. Three immunities is pretty cool (doesn't beat Gengar, who has 4 immunities), but that's Spiritomb's weakness. He can't freely switch into something he's not immune against, because he'll always take normal damage.
Anyways... Aerodactyl.
You'll really want to breed for a Jolly nature. Much like people criticize Starmie's dull 100 base Special Attack, I'll say that Aerodactyl doesn't have as amazing Attack as he seems (105 base). The only thing really going for him is his utterly insane Speed. Here's my opinion for a moveset:
- Stone Edge
- Earthquake
- Crunch
- Stealth Rock
The notorious lead of Cema. Perhaps more notorious than my Spiritomb lead. Fix him with a Focus Sash in case you can't get an OHKO or a KO, and then throw a quick Stealth Rock out before he himself is KOed. Crunch is enough to OHKO things like Gengar or Starmie leads, (barring Focus Sash of their own), and will OHKO Alakazam (although, someone would have to be crazy to send Alakazam in against Aero without a Choice Scarf), Stone Edge is for STAB, and Earthquake basically hits everything that resists Stone Edge.
Aerodactyl can survive a lot longer with common sense; if something fragile is sent in against it (like Alakazam or Gengar), you've gotta assume it's a Choice Scarf Pokemon. And if Aero is already injured (thus rendering Focus Sash useless), it's best to switch out to a wall in order to play it safe. That's why I'll always Drill Peck an Aerodactyl, even if it resists it, it still makes him a lot less scary being able to be OHKOed.
Sorry for the long, long response. Aerodactyl is an awesome Pokemon, and I know from experience the kind of havoc it can wreck if you don't know how to handle it.