Kabuto--Kabutops FTW. I just loved it when I first saw it in Pokemon Yellow and in the anime a long time ago.
What I would like to see is Fossilize Dragon type. Though I think it would have more then 2 weakness but with a good background story on it I wouldn't care.
The reason I think they are part rock type is simply because they are revive from fossils. So they still have rock minerals in their DNA and what type they use to be.
Example Water/Rock, Flying/Rock etc.