How do you get sheldon in Pokemon platinum?

Answer 1

to get shieldon you need to under ground and find the armor fossil then put it in your bag next go up to oreburgh city and talk too the guy in the museum, but you need five Pokemon in your party then tell him about the armor fossil and go out of the museum then go back in then talk to him again he will give you shieldon lv.20,you can do this with any other fossils you find.

sources:

http://www.serebii.net/pokedex-dp/410.shtml