COMPARING COMMON SAMPLING METHODS FOR FOSSIL MARINE-INVERTEBRATES IN THE BELL SHALE FORMATION (MIDDLE DEVONIAN) OF MICHIGAN

Achieving an accurate description of species richness and abundances in an ecosystem is a fundamental objective for many ecologists and paleoecologists, with the most common collecting methods for fossils being surface or bulk sampling. In this study we compared the differences between surface and bulk sampling the Middle Devonian Bell Shale Formation to accurately capture the formation’s macro-invertebrate faunal assemblage using rarefaction curves. Spoil piles of the Bell Shale Fm. from the Calcite Quarry in Roger’s City, Michigan were surface and bulk sampled in 2019 and 2020. In 2019, 19 liters of matrix were bulk sampled and about two hours were spent surface collecting. In 2020, 28 liters of matrix were bulk sampled and about one hour was spent surface collecting. All samples were collected by the same individual, the bulk samples were screen washed using #10 mesh (2 mm openings), and specimens over 75% complete were identified to the genus level using the published literature and the invertebrate paleontology collection at the University of Michigan. Twenty five genera were identified, with 14 genera being captured in the surface collecting. Despite doubling the bulk samples between 2019 and 2020, they produced 310 and 313 identifiable specimens, respectively. However, 11 new genera were collected in the 2020 bulk samples. This was not unexpected, because the rarefaction curves for the 2019 bulk sample had not plateaued, unlike the 2020 bulk sample. The 2019 and 2020 surface collecting produced 135 and 210 specimens, respectively, but neither rarefaction curve had plateaued. This study indicates that just over 300 identifiable specimens is needed to accurately characterize the generic richness and abundances of the macro-invertebrate faunal assemblage of the Bell Shale Fm. in the Roger’s City area and the rarefied extrapolation curves predict that a sample size of 500 to 600 identifiable specimens is needed to capture any remaining rare taxa.