Enigmatic Mazon Creek Tully Monster
Tullimostrum gregarium

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 coal mines, 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. This specimen is a nearly complete example of the famous Tully Monster, named for Francis Tully who first collected it in 1958. It is endemic to Illinois, and is the state fossil. It shows the feature posterior to the “eye bar”. The true affinities of this mystery animal are not known, some scientists think it may be related to the Gastopoda (snails), but this is far from decided at this point. Tullys are not often seen in a complete state, and this is a fine specimen missing only the grasping appendage. A complete one would be worth well over triple the asking price of this large specimen.