Originally I thought this was a branching dendrite but after studying it, appears to be a graptolite fossil. It might be a Desmograptus, Dictyonema, or unidentified graptolite. I do not have much literature on these creatures to make a good guess.
This fossil has great contrast in relation to the limestone!
Fossil found in the Louisville Limestone (Middle Silurian Period) of Jefferson County, Kentucky, USA.
UPDATE (2020): I was contacted by Dr. Jörg Maletz of the Institut für Geologische Wissenschaften at Freie Universität Berlin and he would like to study this specimen to see if it is a Ptiograptus percorrugatus. Now I just have to find out where I put it.
