Skeleton Skulls *minor spoilers for Dorn*

I just fought some skeletons before I found a certain Necromancer on the same map. They all had a skull as a lootable item (unlike the named skeletons fought later). Are they of any significance or just an oddity?

I should also mention that I've only just fought with the Necromancer, so I'd appreciate if people would refrain from mentioning any spoilers past that point.