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Cincinnati, OH, United States

Vendrasco M.J.,California State University, Fullerton | Checa A.,University of Granada | Heimbrock W.P.,Dry Dredgers | Baumann S.D.J.,Midwest Institute of Geosciences and Engineering
Geosciences (Switzerland) | Year: 2013

Nacre was previously thought to be primitive in the Mollusca, but no convincing Cambrian examples are known. This aragonitic microstructure with crystal tablets that grow within an organic framework is thought to be the strongest, most fracture-resistant type of shell microstructure. Fossils described herein from the Ordovician of Iowa, Indiana, and Ohio provide supporting evidence for the hypothesis that sometime between the middle Cambrian and late Ordovician, nacre originated in cephalopod, bivalve, and possibly gastropod lineages. The correlation of independent origins of fracture-resistant nacre with increasing shell-crushing abilities of predators during the Cambrian-Ordovician suggests an early pulse in the evolutionary arms race between predators and molluscan prey. © 2013 by the authors; licensee MDPI, Basel, Switzerland. Source

Thomka J.R.,University of Akron | Brett C.E.,University of Cincinnati | Bantel T.E.,Dry Dredgers | Young A.L.,University of Cincinnati | Bissett D.L.,Dry Dredgers
Palaeogeography, Palaeoclimatology, Palaeoecology | Year: 2016

Diploporites, like most pelmatozoan echinoderms, are characterized by complex multi-element skeletons prone to complete disarticulation if left exposed for extended periods of time. Consequently, preservation of abundant articulated diploporite thecae is rare and generally restricted to environments where rapid burial events could catastrophically entomb individuals. One such environment is represented by the lower portion of the Wenlock-age Massie Formation at the New Point Stone quarry near Napoleon, southeastern Indiana, which we recognize as a Konservat-Lagerstätte. Yet, taphonomic evidence does not support live burial. Diploporites (Holocystites spp.) are dominantly preserved as intact thecae without any portions of brachioles and with damage (plate shifting and plate loss/plate jumbling) on one side. Post-mortem encrustation is common, but epibionts are typically present on the well-preserved sides of thecae. Geopetal sediment-fill of thecae shows that the well-preserved side commonly faced upward following burial. This taphonomic state is paradoxical, as burial of live diploporites would have resulted in preservation of complete individuals with no encrusters and only compaction-induced damage; rapid burial of diploporites following a short interval of exposure would have resulted in preservation similar to observed patterns, but with encrusters and geopetal infills indicating that the poorly preserved side faced up; and burial after extended exposure would have resulted in thorough disarticulation of thecae. Rather, a variable and, in some cases, complex taphonomic history is suggested for diploporites from the Napoleon quarry, with at least some individuals having experienced one or more brief episodes of exhumation prior to final burial. Early diagenetic cementation of initial theca-filling sediment is the most likely mechanism for keeping thecae intact during subsequent exposure. © 2015 Elsevier B.V. Source

Dattilo B.F.,Indiana University - Purdue University Fort Wayne | Freeman R.L.,University of Kentucky | Peters W.S.,Indiana University - Purdue University Fort Wayne | Heimbrock W.P.,Dry Dredgers | And 5 more authors.
Palaios | Year: 2016

Small fossils are preserved as phosphatic (carbonate fluorapatite) micro-steinkerns (∼0.5 mm diameter) in Upper Ordovician beds of the Cincinnati area. Mollusks are common, along with bryozoan zooecia, echinoderm ossicles, and other taxa. Similar occurrences of Ordovician micromorphic mollusks have been interpreted as ecologically dwarfed and adapted to oxygen-starved conditions, an interpretation with implications for ocean anoxia. An alternative explanation for small phosphatic steinkerns is taphonomic. Stable carbonate fluorapatite selectively filled small voids, thus preserving small fossils, including larval/young mollusks. Reworking concentrated small phosphatic steinkerns from multiple generations while larger, unfilled calcareous shells were destroyed, resulting in small fossils progressively replacing larger fossils. With thin sections and insoluble residues, we document evidence that many of these steinkerns are incomplete ("teilsteinkerns") recording small parts of larger, normal-sized animals, or juveniles, along with smaller species. This finding suggests that these fossil assemblages are taphonomically, not ecologically, size-limited. Based on the ecology of modern oxygen minimum zones in which shelled mollusks are rare, the presence of abundant shelled organisms actually argues against severe oxygen stress. Our results also imply that the process by which the "small shelly fossils" of the Cambrian were preserved continued into the Ordovician. Copyright © 2016, SEPM (Society for Sedimentary Geology). Source

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