Complex sentence: The skull was toothless and had a prominent sagittal crest, only the base of which was bony: the front of the crest featured a tall bony rod extending up and back, and the rear of the crest had a long prong of bone projecting behind it.
Split into simpler sentences: The skull was toothless and had a prominent sagittal crest, the base of which was bony. The front of the crest featured a tall bony rod extending up and back, and the rear of the crest had a long prong of bone projecting behind it.