5.3" Alethopteris Fern Plant Leaf Fossil Carboniferous Age Llewellyn FM ST Clair, PA

Location: Llewellyn Formation, St Clair, Pennsylvania

Weight: 6.9 Ounces

Dimensions: 5.3 Inches Long, 4.1 Inches Wide, 0.7 Inches Thick (Plate)

Comes with a Certificate of Authenticity.

Comes with a Free Stand.

The item pictured is the one you will receive.

Pennsylvanian Age, 300 million years old.

Alethopteris Sp Fern Fossil

These remarkable plant fossils hail from the Llewellyn Formation, dating back approximately 300 million years to the Pennsylvanian Period. This formation is one of the rare sites where collectors can find highly detailed ferns, often preserved in white or pale yellow against the striking contrast of black shale.

During the Pennsylvanian, these plants fell into swampy environments where low-temperature, high-pressure, and low-oxygen conditions allowed the plant tissue to slowly mineralize. Initially, pyrite (from sulfides) replaced the organic tissue, and later, as sediments accumulated and pressure and temperature increased, pyrophyllite (aluminum silicate, whitish in color) replaced the pyrite.

The most commonly preserved ferns include Alethopteris, Neuropteris, Pecopteris, and Sphenophyllum, many of which belong to families that are now extinct, such as Macroneuropteris. These fossils provide a window into Carboniferous and early Permian swamp ecosystems, when ferns, horsetails, and club mosses dominated the landscape. By the end of the Carboniferous, tree-sized club mosses and horsetails declined due to disappearing swamps and cooling climates, though some coal swamps persisted into the earliest Permian, forming coal seams with plant and root layers.

Excellent specimens are typically found in thinly laminated shale layers, which split easily with a chisel or splitting hammer, making them accessible for fossil collectors, paleobotanists, and educational displays. These fossils not only highlight the diversity of ancient plants but also preserve the intricate details of prehistoric ferns.