These are experimental. There are not many museum casts out there with gastralia and pre-pubis. Not many pre-pubis bones are preserved, either. I used as a source the MN 6588-V tapejarid, scaled for Tapejara. It shows a pair of pre-pubis bones. They are flat, so I can only speculate about their shape, but since they articulate with the pubis, and gastralia bones, which articulate with the ribs to make a rounded belly, I believe they are concave on the ventral side. That’s also what reconstructions of other pterosaurs suggest. I am not sure yet if I will be able to use them, since there is a lot of speculation in that part of Tapejara’s body (unknown number of dorsals, sternal ribs, etc.)
Here is the pre-pubis I cut out of a 2mm sheet of foam, based on the MN 6588-V specimen.
I made gastralia from pieces of foam like this.
They are probably not thin enough. But hey, maybe this Tapejara had a stiff belly 🙂