Fossil Shark Egg Casing (Palaeoxyris prendeli) - DLD 3703Palaeoxyris sp. and other shark egg cases were discovered roughly 175 years ago and because of their association with plants material in Mazon Creek concretions they were initially classified as plants. Not all researchers agreed, and only years later was the relationship with modern forms of spiral shark egg capsules established. These long, narrow, spindle shaped fossils have surfaces marked by weak spiral lines in a helix. At least 9 species of