I was joined today by long-time excavators Keith, Mike, Josh, and Carter to help with the home stretch of the excavation. All our efforts at this point are focused on removing the last dentary remaining in the pit. We’ve run into two major difficulties with this. First, there is turning out to be a tremendous amount of bone in the wall immediately behind the dentary. Since we’ve already removed a mysticete squamosal from this area, and the remaining bones have complex shapes, I’m loathe to plow through them to recover the dentary.
The second problem is that the dentary is badly broken, with the front third detached and sitting lower in the bonebed. This is somewhat visible in the image above, but it’s even more clear in a low angle view:
This presents us with a jacketing problem that has no good solutions. Ideally I’d like to keep the dentary together in a single jacket. However, this would require a complex bracing system because the bone is already broken and separated by several inches vertically. It would also require making a trench directly through all the possible cranial bones I’m trying to save in the back of the pit.
The alternative is even more complex. We could separate the dentary into two jackets, dividing it at the current break point one third of the way back from the front. That leaves the front third of the dentary to be removed with the other bones. The problem here is the nature of the break. The back part of the dentary (the higher part) is steeply angled, so that the edge of this part of the bone actually ends up under the (otherwise lower) anterior part. This is most clearly visible in this image, taken near ground level:
The higher, posterior part is on the left, the lower, anterior part on the right. The angled fragment in the middle actually ends up below the anterior part.
To get this out, we would have to tunnel underneath the broken area, then jacket the back part. But then we couldn’t immediately flip the jacket; if we did so, it would break the anterior portion. So we would have to dig out under the jacket, then slide it sideways until it was clear of the anterior part before flipping it. It’s a crazy difficult jacket to pull off at Carmel Church without breaking anything, but it’s the best way to protect the bones in the wall, so that’s what we tried.
Having made the decision, it took several hours of preparation work to get the bones ready, but by late afternoon the jacket was made and ready to pull to the side. Here’s the result:
It all worked perfectly. We were able to separate the two parts of the dentary with no significant damage to either side (a crack that was already present opened slightly, but we were able to close and glue it easily).
Tomorrow we’ll make the bottom jacket, and try to decide what to do with the remaining bones; either remove them, or put them under a temporary jacket until the next excavation (which is coming up pretty soon).