Fossil Coprinoscolex, Earliest-Known Echiuran from Mazon Creek

Description: 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 exquisitely preserved specimens are found in the ironstone nodules that make up the deposits. The majority of collecting areas are the spoil heaps of abandoned coalmines, the most famous of which is Peabody Coal Pit 11. Pit 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 seen here was colloquially termed a “leech”, but is actually a member of the obscure phylum Echiura, close relatives of the annelid worms. It is thought that the segmentation seen in some fossils (as here) is the result of contraction of the skin due to the shock of burial. Members of the Phylum are commonly called “spoon worms”