NEW PERSPECTIVES ON PRESERVED TURDS: APPLICATIONS OF X-RAY TOMOGRAPHIC MICROSCOPY IN THE STUDY OF COPROLITES AND OTHER BROMALITES

Bromalites, including coprolites and affiliated trace fossils, offer a rare glimpse into the feeding, digestive, and excretory behaviors of their producers whilst simultaneously capturing unique paleoecological and paleoenvironmental information. Examination of such fossils typically requires sub-sampling of the specimen, often employing destructive sampling techniques (i.e., disaggregation or dissolution) to either a portion or the entire specimen. Recent studies have utilized three-dimensional imaging techniques, such as x-ray tomographic microscopy (µCT), as a non-invasive alternative to reveal macroscopic and microscopic inclusions. Besides the quantitative advantage of producing volumetric renders of coprolites is the ability to survey and target regions of interest that might be well-suited to subsequent thin sectioning or elemental analyses. Challenges with the methodology do persist, often owing to the attributes of the sample. For instance, due to the similarity in composition between the phosphatic matrix and bone inclusions, these features can be difficult to discern via standard segmentation techniques such as thresholding, as both materials occupy the same greyscale range. The lack of contrast is exacerbated by in-vivo digestive processes or taphonomic alteration wherein the bone margins can become diffuse. Consequently, generic-level taxonomic information of skeletal inclusions is frequently not possible. Nevertheless, for coprolites and inclusions that have not been significantly altered, µCT proves to be a powerful tool in extracting additional structural and taphonomic information that might be lost via physical extraction methods.

Herein, we employ µCT in two separate case studies to explore the taphonomic characteristics of the inclusions, including their taxonomic resolution, degree of fragmentation, and proportion of bone material (and other inclusions) to the matrix. The first subset examines terrestrial mammalian coprolites from the Eocene Pipestone Springs Main Pocket assemblage, Renova Formation, Montana. The second includes fish coprolites and possible regurgitates from the Upper Cretaceous Smoky Hill Member, Niobrara Chalk, Kansas.