The compression state of preservation of carboniferous lepidodendrid leaves

Abstract

The lycopod leaf compression fossil known as Cyperites is usually found preserved on rock surfaces as simple, planar coaly ribbons. When sectioned intact in the matrix these leaves are seen to have a complex three-dimensional form. The leaf compression has the form of a “butterfly” when seen in transverse section, consisting of four coaly “wings” linked by a central, horizontal coaly plate. Reassembling part and counterpart of these leaves shows that the fracture plane exposing the leaf may take one of several pathways through the leaf compression. These produce different surface structures on the exposed leaves. Experimental modelling using artificial materials to represent leaf and matrix gives an insight into the fossilization mechanisms leading to the formation of the leaf compression Cyperites. A comparison is made between Cyperites, as seen in transverse section, and the leaves borne on Lepidodendron wortheni. It is demonstrated that there are at least two fundamentally different types of leaf borne by the lepidodendrids represented as compression fossils. A neotype is designated to clarify the application of the name Cyperites, and the status of the type species Cyperites bicarinatus.