The raptor skull I received as a 3D scan of an actual raptor skull. The skull had been smashed and flattened buy the dirt and rocks sitting on top of it for Millenia. So I first un-flattened the skull then by mirroring parts of the skull around came up with the most complete half of a skull possible, then mirrored that to form a whole skull. The other skulls were sculpted in ZBrush.