5.5" Fossil Horsetail (Annularia) Nodule Pos/Neg - Mazon Creek

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.

Annularia is the form genus of leaf clusters of tree-like sphenophytes (horsetails) known as Calamites.

Leaves on Calamites trees formed in clusters of 8 or more, called whorls, at spaced nodes along stems. Annularia indicate flat, starburst-shaped whorls, but the shapes of the leaves themselves could vary from oval (A. sphenophylloides) to lanceolate or needle-like (A. radiata). They can also be identified by midline veins throughout the leaf from node to leaf tip.

We use these terms to describe the shapes of fossil imprints. Exact species are often difficult to determine, but these form taxa help to distinguish the prolific species of sphenophytes that defined the Carboniferous Period.