SEXUAL DIMORPHIC VARIATIONS AMONG CRETACEOUS HETEROMORPHIC AMMONITES OF A PIERRE SHALE NODULE

In 2017, an investigative study was performed on an ammonoid specimen from a Campanian-aged nodule obtained from the Pierre Shale Formation in Montana. The specimen was determined to be a microconch of Hoploscaphites nodosus. The nodule also contains a significantly larger specimen encased in a highly indurated matrix of black shale. It is hypothesized that the large specimen may be a macroconch of H. nodosus.. Using a microabrasion unit, the matrix will be removed from the larger specimen. Multiple abrasives will be tested to determine the ideal medium to remove the indurated matrix from the specimen. The specimen will then be examined using a camera lucida to image sutures and identify the species and the possibility of sexual dimorphism. The sample will also be measured, and conch characteristics will be quantified using standard calculations. Features, including ornamentation and any mature modifications, will also be identified. The study objectives are determining best practices in microabrasion of a fossil specimen and identifying the specimen as a possible sexual dimorph to the microconch from the 2017 study on the same nodule.