Wednesday, September 8, 2010


This fossil is the cone of a extinct Lycopod (Lepidodendron, Sigillaria) or possibly Horsetail (Calamites) that came from St. Clair, Pennsylvania.

It was found in the black shales of the Llwellyn formation which is Pennsylvanian in age (Westphalian). The details of the cone are not entirely preserved due to the nature of the formation. Cones are thick organic structures and these are compression shales. Thus the majority of the organic "meat" of the cone has been squished and turned into coal.

You can see some of the outer edge details and you can see some minor detailing at the base of the cone. The rough looking "layers" that you can see in the fossil is likely just coal fractures and do not represent any real cone structures.

A related find from the same trip is this Lepidostrobophyllum bract or sporophyll. It's a part of a much larger cone that belonged to a Lycopod like Lepidodendron or Sigillaria.

Both of these finds are rare for me from St. Clair. Most of what I find at the site are tree fern leaves (Alethopteris, Neuropteris), branches and logs.

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