WTF - "What's This Fossil" - Bone

So here we are again starting on a new block of rock containing a lot of bones. This block is what we call Block 3. In the original group of blocks it was a small block that crumbled between the larger blocks. In this photograph it's the one wrapped in foil to keep it together.

The reason it crumbles is because it's all full of bones. The largest Femur and the first Illium came out of this block and the ones next to it. I wanted to tackle something productive and new.

The first two bones are already not what I expected. The first on I expected to be a limb bone, and the second a small sector of a centrum. Big surprises on both of them!
Here is the one I first thought was a section of Centrum. However, a little excavation shows it is not a centrum, but is something else.

 After a little more preparation, a split or bifurcation starts to appear. Perhaps it's another skull bone!

 Maybe the back end of the skull, including a brain case and the arch going over to the quadrate.

More excavation reveals a bridge (concave) bone between these two sides. WTF?

A partial neural arch and centrum appear, tucked under the edge of the bone. Sometimes I feel like the bus driver who said "It's much easier to keep to the schedule when you don't stop to pick up passengers" In my case it's much easier to excavate bones when you don't have to work around other bones that you find!

 As we continue to excavate, it becomes apparent that the end of the bone is quite robust - not at all like a skull, much more like a limb. However, which limb bones have a very distinct C-shaped section?  We do have one such bone, which Eric & Pat have called an Ischium. A 3D printed copy is the brown plastic below.  This would be part of the Pelvic Girdle. However, this new bone is much more robust though not significantly wider.  

 One last picture as it stands at the moment. It certainly is a WTF (What's This Fossil). Once we get it out we'll be able to tell. The good part is that the other end of the bone is in the rest of the block, so we'll have it all eventually.

 In addition to this preparation, I've been printing out pseudo tail bones. I'm now up to 40 bones printed out of a total of 65. These last bones are getting small, so I'm going to try changing over to a smaller extruder nozzle (0.3mm instead of 0.5mm)  and printing in thinner layers (0.1mm instead of 0,2mm). Hopefully this will give us the needed detail. These will total up to be a tail over 5 feet long!
Sincerely, Greg Carr