Fossils from Mazon Creek - Astonishing Carboniferous Diversity

Mazon Creek is a world famous lagerstätten located southeast of Chicago, Illinois in the central United States. The fossils are found in ironstone concretions formed during the Pennsylvanian Period of the Paleozoic some 300 million years ago. The Mazon Creek concretions are noted for containing exquisitely preserved fauna and flora, including the soft tissues that rarely fossilize.

Mazon Creek fossils are within the lower portion of the Francis Creek Shale that is some 25 to 30 meters thick, the result of a tropical river delta system that was located about 10 degrees north of the equator during the Carboniferous.

The Mazon Creek flora is believed to comprise more than 400 species among 130 genera. More than 300 animals have been identified, including cnidarians, worms, snails, clams, shrimps, eurypterids, fish, hexapoda (including insects, millipedes, centipedes), arachnids (scorpions and spiders) amphibians, and horseshoe. This astonishing diversity makes Mazon Creek important to paleotological science.