On occasion, a paleo-pen pal emails me a few images of unusual material (I would consider most of what's sent "unusual," anyhow) he's pulled out of various places.
Latest example is in the photograph, below. It's a slab of shale from a lower Ordovician section of the Palmetto Formation, Nevada, that contains carapaces (original phosphatic shell substance preserved intact, by the way) of the curious, extinct, bi-valved phyllocarid crustacean called Caryocaris. The critter seems restricted worldwide to strata of early to mid Ordovician geologic age (a handful of examples assigned to the Silurian are apparently problematic)--sometimes occurring in "graptolitic shale facies."
I'd never even heard of these things until I received this image. Had to do some research, indeed. Not something most folks see everyday, I'm thinking.