This is certainly a card of discovery. The man uncovering the skull represents for me the sun; he is bringing light to the situation where only darkness was before. That's the first level of the card. The more difficult piece for me is what he is discovering. The skull is three things to me: as a piece of the skeleton it is a foundational piece of some greater whole; as a decorated object it may be a ceremonial object, and therefore a talisman of some kind; as a bone it is old, and represents age and death. The Booklet suggests that this card represents "Reality," which I don't disagree with, but doesn't go far enough to satisfy me. I sense that the man hasn't just happened upon the skull, but has encountered something he was looking for. This doesn't strike me as a random encounter, but one that took time and perseverance. That said, I can't tell if the skull is some missing component to something that the shaman wants to accomplish, or some malignant influence causing a disturbance that he seeks to end. Either way, I feel that this skull is the key piece to something that the man is seeking to resolve.
More numerologically, the fours tend to be cards of balance and steadiness. While three is the magic number, fours are totally dependable, often times to their own detriment. I suppose it's not without merit that the uncool are labeled squares, or that the innovative are always trying to think outside the box. That said, we need the box to stand on in order to get outside of it, and I prefer tables with four legs to three, and a car with four wheels to a motorcycle with two. I think that's part of the reason why the discovery of the skull suggests resolution to me, because of the steadiness that comes with four.