This is Mazon Monday post #116. What's your favorite Mazon Creek fossil? Tell us at email:[email protected].
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Coprinoscolex elliogimus is an animal long referred to by collectors as the "Leech". More recent research now shows it to be an echiuran, which are commonly called "spoon worms". They are deposit feeders living in shallow water, in rock cracks and crevices, or even under boulders. Like leeches, they are also Annelid worms. Being a soft-bodied animal, echiurans are rare in the fossil record with C. elliogimus is the earliest known occurrence.
C. elliogimus was described in 1977 by Douglas Jones and Ida Thompson in "Echiura from the Pennsylvanian Essex Fauna of northern Illinois".
Abstract
The first unequivocal fossil echiuran, Coprinoscolex ellogimus gen. et sp.n., is described from the Middle Pennsylvanian Francis Creek Shale of the Mazon Creek area of northeastern Illinois. Specimens are whole-body impressions within siderite concretions. They show anterior proboscides, cigar-shaped trunks, convoluted alimentary canals, and cylindrical pellets. Lack of setae suggests classification in the Family Bonelliidae. Coprinoscolex was most likely a marine deposit-feeder, either crawling over the sediment surface or burrowing to shallow depths while ingesting sediment. While this occurrence does not confirm or deny an annelidan ancestry for the Echiura, it indicates that by the Pennsylvanian, echiurans were unsegmented and essentially modern in form.
Ida Thompson is an American invertebrate paleontologist who identified many Mazon Creek worm-like animals in the late 1970's and early 1980's. She is also known for writing "The National Audubon Society Field Guide to North American Fossils", a book that has inspired many young paleontologists. Doug Jones is an American paleontologist that has published extensively on the geology and paleontology of Florida.
C. elliogimus appears on pages 13 and 14 of "The Mazon Creek Fossil Fauna" by Jack Wittry.
Coprinoscolex ellogimus Jones and Thompson, 1977
This plump, cigar-shaped animal has long been called a leech by collectors, but recent investigations have designated Coprinoscolex ellogimus an echiuran, the earliest known in the fossil record. It was a marine, shallow-water deposit feeder. Pellets in the body gut area are a prominent field mark and consist of ingested mud serving as a substrate to which digestive tract bacteria anchor themselves. C. ellogimus is smooth skinned, without setae or any hard parts. Segmentation often appearing on the fossil specimens is caused by contraction of the skin due to the shock of burial.
Modern echiurans are commonly called Spoon Worms as their spoon-like proboscises form from a flattened structure rolled into a cylindrical tube. Though modern spoon worms have fleshy proboscises, examples of well-preserved proboscises in fossil specimens are rare (see Figure 13.2 below) and their exact structure is unknown.
Specimens
From "The Mazon Creek Fossil Fauna" by Jack Wittry
Recent find by ESCONI member Rich Holm. This specimen has the gut line and the fecal pellets.
