The bone on the bottom left is another quadrate. We have several of these, all different sizes of course. This one is smaller than the others, and has an extremely thin web of bone between two depressions. The web ended up being held together entirely by glue since it was only about 1/10 of a mm thick! The bone on the bottom right is a broken illium (pelvis bone) with a piece of rib stuck on the side. Nothing exciting, I've prepared a half-dozen of these. Actually, 7 years ago I would have died and gone to heaven about finding one of these!
The one in the middle is very special. I have a partial one of these from a bigger animal, but neither I nor the guys in Alaska knew what it was. It is long and skinny with a V-shaped cross section. I don't think the bone is more than 2 mm thick anywhere. Most is less than 1 mm thick - very time-consuming to prepare! (about 12 hours AFTER I got it out of the rock). I think it is a parasphenoid. This bone lies in the mid-line of the palate, between the pteregoids, and we haven't found one of these (before now, of course!). The second picture shows it in end-view - you can see how thin it is.
Here is how parasphenoids fit in a skull, looking at the bones of the roof of the mouth. They are found in everything from fish to mammals, so it makes sense they would be in thalattosaurs too. Blue bone is the parasphenoid, ptr is the pteregoid.
Here's one from a modern fish:
Last of all, at the top of the picture is a long, twisted bone. I don't know if it was twisted in life, but judging from the parasphenoid it must have been twisted before burial since it was right next to it and is much more robust. It was not twisted during burial nor afterwards in the rock - the rock has not been distorted like that.
However, I don't know what it is! It roughly resembles a rib, but it has a triangular cross-section and a decidedly non-rib thick end. At 7 inches long, it a significant bone - if we only knew what it was!
Anyway, I am still