C. Pennsylvanian, Carboniferous Period – 300 million years old

An interesting positive and negative of the fern from Mazon Creek, each half in an iron stone nodule with another fern to reverse.

Ferns have leaves which are called fronds, and consist of leaflets, but some have undivided or entire fronds. Reproduction is by spores found on the underside of the fronds or can rarely be produced on specialized fronds. They can vary in size from large tree ferns to minute filmy ferns.

A nice example with good detail.

Size of Fern: 40mm to 81mm

Nodule: L: 95mm x W: 59mm x D: 11mm approx