20 August 2004

A fern fossil (genus Percopteris)

Bill Dembowski, Fellow of the Royal Astronomical Society

As further proof that the wonders of nature are all around us, here is a fossil that I unearthed less than a mile outside the city limits of Johnstown, Pennsylvania (population 25,000). Southwestern Pennsylvania is coal country, and many of the fossils found in this area are of plants that date back to the Pennsylvanian Period of the Paleozoic Era (280 million to 325 million years ago).

Not to be confused with modern ground dwelling ferns, Pecopteris was part of a tree-like plant that reached heights of 15 meters (50 feet) or more and had a base over 1.5 meters (5 feet) in diameter. This huge tree fern managed to achieve such great heights by reinforcing nearly the entire length of its trunk with its roots. What we actually see in this fossil is not the plant in its entirety (known as Psaronius), but just the "leaves of a tree."

To see a sketch of Psaronius with its crown of Pecopteris go to: Fossils in Southwestern Pennsylvania (University of Pittsburgh) http://www.geology.pitt.edu/GeoSites/ppsaronius.jpg