The Dome Fossil is a fossil that Kabuto can be resurrected from.
It can be obtained from Mt. Moon, and can be resurrected at the lab in Cinnabar Island. For Diamond, Pearl, and Platinum it can be obtained from the Underground after receiving the National Dex, and can be resurrected from the museum in Oreburgh City.
In Pokémon FireRed and LeafGreen at Mt. Moon, if you take the Dome Fossil, then at Fushia City, there will be a Kabuto. If you don't choose the Dome Fossil, an Omanyte will be there.