Cone

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.

Alethopteris

Alethopteris is an ancient seed fern that lived in the Pennsylvanian period about 306 million years ago. It's another common fossil that I find at St. Clair, PA from the Llwellyn formation. Back then there was a small variety of trees most of which fell into three catagories: Lycopsids (Lepidodendron, Sigillaria), Cordiaites, Articulates (Calamites) and Seed Ferns such as Neuropteris, Alethopteris and Pectopteris. This branch, no pun intended, of plants died out sometime in the Cretaceous but we have an idea of what they might have looked like when we view modern Tree Ferns (considered True Ferns) such as this example from New Zealand.




Here are some examples of Alethopteris from St. Clair. It is a very common plant at the site and can often be found covering whole slabs of shale with overlapping fronds.



I like when I split a slab and get a nice pair of leaf impressions.

Sphenophyllum

Sphenophyllum is a commonly found fossil in the shales of the Llewellyn formation at St. Clair, PA.

Sphenophyllum is part of the Horsetail family and is generally thought to be a creeping or climbing plant that may also have been an understory shrub in the lycopsid forests (Lepidodendron, Sigillaria). As is the case with many fossilized plants from the Pennsylvanian, the generic name Sphenophyllum originally included only impressions/compressions of certain leaves, but has come to include several types of leaves, stems and roots. Early paleontologists were looking at fragments of the plant without a good idea of how everything fit together. As a result they gave genera level names to many different parts of the same plant. Today we know more about what the plants looked like thanks to some well preserved fossils and much detective work but we still retain some of the various names given to the parts.

I usually find sections of the stem with some leaves attached as whorls around segments.







I think this piece is a segment from a branch with some of the thinner, more needle like leaves.




This is a single whorl of leaves that separated from the branch and looks like a flower, however flowers would not develop for another 100 million years. The preservation is fairly good and you can see the veins in the leaves.




For a great illustration of a Sphenophyllum reconstruction, see this post from the Fossil Forum.

This UMCP of Berkely page has a nice page that discusses the origins of Sphenophyllum.