Diminutive Mazon Creek Jellyfish Fossil
Time: Pennsylvanian (~300 million years ago)
inch): 8 mm across (including tentacles) on a 20 mm by 18 mm nodule
Mazon Creek, Pit 11, Francis Creek shale, Braidwood, Illinois
The Mazon Creek deposits of the region near Braidwood, Illinois
rival the other famous Lagerstatten of the Burgess Shale, Solnhofen,
and Liaoning for the variety of detailed life preserved. Many
specimens are found in the ironstone nodules that make up the deposits.
The majority of collecting areas are the spoil heaps of abandoned
coal mines, the most famous of which is Peabody Coal Pit 11.
11 now serves as a cooling pond for the Braidwood nuclear power
plant, but with over 100 other localities, specimens still come
to light. The example here is a small jellyfish known as Octomedusa
pieckorum. It derives its generic name from the fact that it
8 tentacles which vary from mere nubs to ones that extent out to
a length equal to the diameter of the bell; several are visible
here. The indistinct cross-like structure is thought to be the
mouth. Members of the Coronatida today contain the smallest extant
jellyfish. This one represents an opportunity to add this rare
to your collection of Mazon Creek fossils.
fossil pictures to enlarge