Enigmatic Mazonova Paleozoic Vertebrate Egg Mass

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 nodule contains an example of Mazonova, a rare fossil believed to be the egg mass of a fossil vertebrate, and was found at Pit 11 just last year. Other than egg cases of sharks such as Paleoxyris, fossilized eggs from the Paleozoic are almost unheard of. At the time of the writing of Ricjhardson’s seminal work on Mazon Creek Fauna less than a dozen specimens were known, most of them held in museum collections. I was recently able to obtain this example from the person who collected it in the field. It is not clear as to whether the specimen came from freshwater, brackish, or marine deposits as they are known to intermix. To me they look all the world like amphibian eggs found today in freshwater ponds in early Spring.