Fossil Fern (Pecopteris) And Horsetail (Calamites) - Mazon Creek

This is a fossil fern (Pecopteris) and horsetail (Calamites) from the Carbondale Formation, Coal City, Illinois. It is preserved inside an ironstone nodule associated with the famous Mazon Creek Lagerstätte. The fern is 2.7" and the horsetail is 1.6". Under magnification the detail of this specimen stands out.

Pecopteris is a form classification (taxa) for the leaves of a fern associated with the tree fern Psaronius. It is one of the most common Pennsylvanian age plants and grew up to ten meters, or thirty feet, tall and produced about 7,000 spores per leaf.

Calamites is an extinct genus of jointed-stemmed plant, closely related to horsetails. It is most often know from its form taxa, Annularia. This is where the leaves or whorls are given their own taxanomic description as part of the larger plant.

The Mazon Creek fossil beds are a deposit with exceptional fossil preservation, known as a conservation lagerstätte, located in Illinois. This location of late Paleozoic (~307 million years old) biota ranks among the great fossil sites around the world. The large variety of fossils collected here vary between plants and animals, including soft-bodied and insect preservations. Fossils from this site are often quite detailed and are preserved within siderite (iron carbonate) nodules.

Over 500 animal and 200 flora species have been described from Mazon Creek. The event that caused this die-off and preservation is believed to have started with a catastrophic flood event that buried the biota of the modern day Mazon Creek area. The deposition of river-borne silt and clay, brought on by upland erosion and delta progradation, contributed to the incredible preservation of one of the most complete records of Paleozoic biota.

This site has been collected for more than 100 years, and likely will continue to be collected by both professionals and amateurs for many years to come.