Septarian nodules sometimes are misidentified as turtles, coprolites and other fossils. Septarian nodules are hardened mudballs that dehydrate, crack and fill with minerals. The cracks in this one filled with fluorescent calcite. The ribs that stick out are the calcite that filled the cracks in the mudball.    This nodule was found in calcareous shale from the Late Cretaceous Arcadia Park Formation. The exact age of its formation is unknown but probably occured in the Late Cretaceous.