you're first sneak peek of the RBCM is this rather lovely belemnite. belemnites were very similar to squid (which they were closely related too) but had much harder "guards", aka inner shells, which is what you see here. due to these harder shells belemnites fossilize quite easily (at least this particular part of them).
the belemnites evolved during the devonian period, and finally went extinct in the cretaceous. they reached the height of their success in the jurassic and cretaceous.