It is common that only a few modes of preservation will be be found in one assemblage. Examples of the others will be provided in the big display specimens. Microscopic fossils are abundant in all three of these assemblages, though representative specimens were included only in set 1. Explain how the collecting techniques we choose may affect our understanding of ancient communities. It is known that many living Mollusca, including most Bivalvia and Gastropoda and all Cephalopoda, secrete skeletons composed of the mineral aragonite rather than calcite.
Oysters are an exception and secrete calcite.
Living Echinodermata always secrete calcite skeletons. Geochemists tell us that aragonite is less stable than calcite and in time is more likely to be dissolved by interstitial fluids and ground waters. Now evaluate the relevance of this information to the interpretation of the modes of preservation of this fossil assemblage. Casts and molds provide less information than the original skeletons, so these specimens are more difficult to identify. Reconstruct this ecologic community in the form of a simple sketch showing each animal in its natural position doing what it naturally did.