DB Poli from Roanoke College and her students Travis Lupmkin and Sarah Petrosky have been closely examining our Carboniferous plant fossils from the Boxley quarry in Beckley, West Virginia, in order to make identifications and to look for any unusual features.
The small fragment shown above (note the 5 mm scale bar) includes three pinnae (“leaflets”) from a fern frond. The one in the middle is a typical shape for a complete pinna, but the ones on each side show irregularities in their shapes. Could these be insect trace fossils, evidence of a Carboniferous insect eating ferns?
Here’s a closeup of the left pinna:
There’s a peculiar pattern associated with the missing parts of the pinna. If you look at the sediment underlying the plant, everywhere the pinna is missing, the sediment is a different color and grain size. I think this is not a trace fossil; instead, I believe the fossil plant broke at those points and exposed a slightly deeper layer of sediment.
How about the other pinna? Here’s a closeup:
The image is oriented so that the missing part is at the top, left of center. In this case there’s no change in the sediment where the plant’s missing. There’s not enough detail preserved here for me to say for sure, but I think there’s a fair chance that this is a trace formed by an insect or some other animal that was eating the fern fronds.