All rodents I studied about (veterinary med) have connected processus zygomaticus ossis temporalis and processus temporalis ossis zygomatici, the ones closing eye socket (which is open in this skull and all the cats in the world). Sorry, English is not my first language so I'll just use Latin and you google if you need to. The separation in the arch between those bone pieces are more characteristic to cats. So I'd bet on a baby cat (you can see the bones have not fused yet, so it must have been less than 6 months old). Also, this skull lacks nasal bones, which are thinner than paper in baby cats (thus easy to destroy/break off when handling the skull, so it's another for-cat clue). BUT since the nasal bones have been removed and the processus zygomaticus ossis temporalis on the left side of the pic was definitely broken off as well, it could be a very broken rodent skull.