On the level The Ark, enter the valley to the right after the wrecked Phantom. Look to the left to find a large boulder.
Use a Ghost to reach the side of the boulder that is closest to the bridge overhead. Get the Ghost up the side of the wall by using the thrust.
Get two Ghosts up the wall to the top of the bridge. Stack them on top of each other next to the last beam at the end of the bridge where the skull is located.
Then, jump from the top of the Ghosts towards the skull and land on the beam. Pick up the skull.
There you go, the Famine skull.
Enjoy!
