The Silurian aged Waldron shale preserves an odd fossil that looks like the roots of a plant (like a bush or tree) but they actually belong to a Crinoid which is an animal. These roots are the holdfast of the crinoid which is at the opposite end of the stem from the calyx and is what it uses to attach itself to the sea floor.
Here is a classic example of this interesting fossil showing a dendritic pattern to the roots. There is also a partial Eucalyptocrinus calyx on the right hand side.
This specimen has some Pyrite crystals that have grown on the fossil and a cluster of bladed crystals near the end of one root that I think are Marcasite.
These are good examples of this unusual method that Crinoids employ to keep themselves stable in the currents. Some crinoids attach to a hard surface like a shell or coral with a warty growth while others are more free floating or mobile. These "root" systems likely developed because the substrate of the sea floor was very soft and muddy and did not provide many hard attachment points.