Coprolites of the late eocene using virtual paleontology from the Pipestone Springs Main Pocket, Montana

Abstract

The study of coprolites and their internal constituents has previously employed a predominantly destructive means of extraction, resulting in the partial or complete loss of the specimen. Recently, however, there have been several studies adopting a more modern approach to data collection and analysis, incorporating three-dimensional imaging techniques such as x-ray tomographic microscopy ([mu]CT) and synchrotron microtomography. These non-destructive methods allow us to virtually extract qualitative information on the identity, structure, orientation, and size of inclusions, as well as important quantitative information with respect to the relative proportions of inclusions to matrix. Herein, [mu] CT was used to study bone, and other miscellaneous inclusions, in two size classes of coprolites from the Eocene Pipestone Springs Main Pocket (PSMP) assemblage (Renova Formation), Montana. Segmentation of [mu] CT-scans has enabled documentation of the degree of skeletal fragmentation and proportion of bone material to the phosphatic matrix which provides novel insights into the feeding behavior of the producer and taphonomy of constituents. Among the features identified in the [mu] CT data were skeletal fragments, including those showing evidence of bone-crushing; delicate molds of hair; lithic fragments encrusted on the coprolite surface; and lastly several pores and cracks throughout the coprolites' structure. A benefit of this technique is the ability to extract quantitative data on bone volumes and diameters for statistical comparison between the two different size classes of coprolite. In combination with volume renders of the segmented material, we also adopt more traditional methods such as thin-section petrography and scanning electron microscopy with energy dispersive spectroscopy (SEM-EDS) to characterize the compositional and taphonomic attributes of the samples. We emphasize that traditional methods are not obsolete, as they provide data that cannot be obtained using digital methods. X-ray microscopy compliments traditional methods insofar that areas of interest can be identified prior to destructive sampling. Overall, this combined approach has provided a means to observe and statistically test differences in the coprolite gross morphology and their inclusions across the two size classes thereby offering valuable insights into the broader paleoecology of the PSMP coprolite producers.