Neither, Aerodactyl is revived from Old Amber. You get Old Amber from a scientist in the Pewter Museum (cut down the tree on the right to get to the other entrance).
The Helix fossil revives into an Omanyte, while the Dome fossil turns into a Kabuto. Both are Water/Rock-types.
In Pokemon LeafGreen, the Dome Fossil can be revived into Kabuto, and the Helix Fossil can be revived into Omanyte.
Neither the Helix Fossil nor the Dome Fossil will become an aerodactyl. In order to obtain an aerodactyl you must revive a pokemon from the Old Amber item which can be obtained in the Pewter City Museum.
If you choose the Helix Fossil it can be revived into an omanyte. The Dome Fossil can be revived into a kabuto. I suggest you pick based on what pokemon you like better.
The Dome Fossil is revived in Cinnarbar Island into a Kabuto. The Helix Fossil is revived into a Omanyte.
Helix fossil turns into Omanyte once you bring it to the Fossil guy on Cinnabar Island in the old Research facility. The Dome fossil turns into Kabuto. And then you can get the Amber from the Museum, which will turn into Aerodactyl
The fossils are obtained in mt moon and the pewter city museum. Either you will get kabuto or omanyte from mt moon depending on which fossil you chose Omanyte=Helix fossil, Kabuto=Dome fossil. Aerodactyl is the old amber you get at the pewter city museum send these to the lab at cinnibar island to get revived!
the dome fossil is one, I just found it !in soul silver you can get the old amber (aerodactyl) and dome fossil (kabuto) you can get them at the Ruins of Alph by smashing rocks and you can revived them at pewter city musseum...
Lilleep (Common) Shelidon (Also Common) Kabuto (Not all that common) Aniroth (BIG FOSSIL but rare) Omanite (Fairly Common) Areodactle (Super Stinkin' rare, I only know there in there because my friend got one after...I don't know how long)...thats about all of them. Oh, you can also get Crainidos (I think)
Helix Fossil - Omanyte Dome Fossil - Kabuto Old Amber - Aerodactyl Root Fossil - Lileep Claw Fossil - Anorith Skull Fossil - Cranidos Armor Fossil - Shieldon -------------------------------------------
skull fossil : cranidos root fossil : lileep old amber : aerodactyl helix fossil : omanyte dome fossil : kabuto claw fossil : anorith armor fossil : shieldon
Dome Fossil = Kabuto (Lv 40, evolves to Kabutops) Helix Fossil = Omanyte (Lv 40, evolves to Omastar) Old Amber = Aerodactyl
When revived, the Dome Fossil will be Kabuto.