Originally I thought this was a branching dendrite but after studying it, appears to be a graptolite fossil.  It might be a Desmograptus ...

These pictures show four different trilobite pygidiums from the Devonian Birdsong formation of western Tennessee, USA.  Identifications o...

A cephalon of a Huntonia lindenensis? trilobite found in western Tennessee.  The fossil was found in the Birdsong Formation of the Lower...