Where Can I Find A Cranidos?

In order to find Cranidos in Pokemon Diamond, you must first go into the Underground. Once you get into the Underground, you then need to start digging into the walls that have treasure and hope that you uncover a Skull Fossil. After you uncover a Skull Fossil and get it added to your treasure bag, you must then go into your treasure bag and send it up to your Bag above ground. After you have done this, fly to Oreburgh City and go into the Mining Museum and talk to one of the scientists in the Mining Museum. He will offer to regenerate your fossil into a Cranidos. Now all you have to do is walk outside, then walk back inside and talk to the scientist again, and he will give you your Cranidos. You might need to have an open slot in your party before he allows you to receive your Cranidos, though. Hope this helps :)