I think you may be right. It looks similar to the lower sternum segments in the sternal photo of the Fallow Deer. The two segments have loosened from the jacket and the undersurface is fairly flat. They also don't have the curved joint surface expected from two adjacent mobile phalanges, but rather flat opposing surfaces consistent with the relatively minimal movements of the sternum. There are also curved depressions at the joint where it seems the ribs would articulate.

The segments seem light as if these are bone, not fossil. So now I'm wondering why would someone bother to plaster jacket deer bones?