A new block - perhaps a new Skull?

I've decided to take a break from preparing block 2 where we have found so many good bones (80+ and counting, including the half-skull). There were some visible bones on block 5 that have been intriguing me since we cleaned them off almost 2 years ago. So while Jerry Dodson continues on the main block, I've switched over for a few weeks. So here is the block 5 as-found. There are about 5 visible bones. The one most intriguing is on the upper right side, close to the light in this picture.

 Here is a closeup. It turns out that these are two separate bones, touching each other. The lower bone, with holes in it, is particularly intriguing as we haven't see such holes in the bones before.

So we set to work with the large air scribe and after about 4 hours work knocked off a block containing both these bones from the main block. Another volunteer, Janet K, will be working on a part of the block that also got broken off inadvertently during the process. It has at least 3 bones, with 2 centrums and another  (limb?) in it. After about 15 hours total work we have these two bones shown, above, now prepared. Both appear to be fragments of a skull, basically because they aren't anything else. But they don't appear to be parts of the skull we have already removed, or even parts of another skull of the same species. For one thing, they are full of tunnels (sinus?) that the existing skull doesn't have.

We already know that we have more than one species of animal here since we have more than one type of backbone. Perhaps this is fragments of a skull of the second animal. But what kind of animal? And the block 5 has at least two more bones that are not recognizable showing on the surface. I'll be preparing them next in hopes that they too are skull fragments.

Sincerely, Greg Carr