This is Mazon Monday post #14.
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Essexella asherae, Species Spotlight
Essexella asharae is the most common animal fossil you will find in the Mazon Creek biota. In the Essex biota, it has been estimated to be over 40% of finds. Specimens come in many forms with varied preservation. While there was a recent paper about whether it is a jellyfish or a sea anemone, the consensus opinion is that it is a jellyfish. The original paper describing Essexella is called "Soft-bodied coelenterates in the Pennsylvanian of Illinois" and was published in 1979 by M. W. Foster. It was included in the book "Mazon Creek Fossils", which was edited by M. H. Nitecki.
Here is just a few of the many specimens from Pit 11 and Braceville that I have been found over the years.
Rob Sula wrote the poem "Ode to a Blob" back in 2002. Rob was 1st Vice-President from 2008-2014.
ODE TO A BLOB
Oh, lowly blob,
Whose grave I did not rob.
On the ground you sit
So round and nicely split.
Were you but a few.
I'd bend to pick up you.
But alas, you're not so rare.
And although I wish I'd care,
I left you lying there.
Rob Sula (2002)
The Creature Corner article appeared in May 1988 and surprisingly was entitled "The Blob".
The Blob (Jellyflsh)
Many are the creatures first discovered In Mazon Creek area concretions, Many are eagerly hunted. Many are truly one-of-a-kind specimens. Many are rare In the fossil record, much sought after by a small army of collectors.
NOT THE BLOB!
What Is this fossil creature that evokes such disdain among concretion hunters? It is a Jellyfish: but being a jellyfish Is not the reason that experienced fossil collectors were and are loath to take the concretion home. Picture yourself on the spoil heaps of Pit 11, prior to their being leveled. Before you rise the slopes - three stories high - a mile long with huge furrows In the Earth. You notice that collectors climb over and past some hills that are virtually paved with Iron slderite concretions. This Is what you have come here to collect. Bucket after bucket Is filled -taken home -and split. All you have are BLOBS! Therein lies the answer -super abundance. How many blobs can a person collect and save?
Jellyfish Blobs as seen on Pit 11 concretions appear as a circular or extended oval color difference on the split concretion. Many have one end slightly flattened and, occasionally, tentacles are seen. The blob may be slightly above the plane of the split concretion. When first brought to scientific attention, some workers considered the blob to be "an artifact of preservation", a pseudo fossil. Literally thousands of blobs with identical configurations doomed that assessment. The warm tropical seas of that period much have been as ideal a habitat for jellyfish as are the tropical seas of today.
Jellyfish are members of the Phylum Coelenterata. Blobs/jellyfish from Pit 11 are placed in the genera Essexella and Reticulomedusa. Both are animals of the Essex fauna, Francis Creek Shale, Carbondale Formation, Middle Pennsylvanian in age.
Strip mines near Peoria, Illinois that mined coal from that same unit have concretions bearing blobs in their spoil heaps. Coelentrate-like fossils have been discovered among the Precambrian Ediacaran fauna of southern Australia and the Cambrian Burgess shale fauna of western Canada.
Andrew A. Hay
