Complex sentence: Due to the shrinkage that the corpse suffered in the bog, the man's actual height is not known, although it is known that he had dark hair, although this too was altered in the bog, and now appears reddish in colour.
Split into simpler sentences: Due to the shrinkage that the corpse suffered in the bog, the man's actual height is not known. It is known that he had dark hair, although this too was altered in the bog, and now appears reddish in colour.