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A diverse, well-preserved assemblage of nautiloid cephalopods was collected from the Treptoceras duseri shale, a 1.5-m-thick claystone within the Waynesville Formation (Late Ordovician, early Richmondian) exposed in southwest Ohio. The strata, the enclosed fauna, and its taphonomy indicate deposition in a low-energy, mud-bottom marine environment, in water depths of 20–25 m, below wave base but within the zone of storm-current reworking.Nautiloid specimens consist of complete conchs that have been replaced by calcite. Twelve species of nautiloids, belonging to eight genera, representative of four orders, have been collected from the shale in southwest Ohio. Longiconic orthocones are clearly the dominant nautiloid morphotype present, with the assemblage dominated by three species of the longiconic orthocerid Treptoceras and with fewer numbers of the endocerid Cameroceras and the slender orthocerid Isorthoceras?, the cyrtoconic oncocerids Oncoceras and Manitoulinoceras, and rare specimens of the orthocerid Gorbyoceras, the oncocerid Zittelloceras, and the ascocerid Schuchertoceras.Nautiloid taphonomy, the diversity of nautiloid taxa present, the lack of postmortem buoyancy in the shells of the more common taxa, the recurrent nature of this assemblage, and the restricted distribution of this Treptoceras–Cameroceras fauna to portions of eastern North America in the Late Ordovician suggest that this nautiloid assemblage represents an in-situ accumulation of nautiloids representative of a living assemblage. These nautiloids were important elements associated with benthic communities in these epeiric sea mud-bottom environments and not simply assemblages of drifted, necroplanktonic shells.

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The Treptoceras duseri shale unit within the Waynesville Formation of Late Ordovician (early Richmondian) age in southwest Ohio and the equivalent Trilobite shale unit in the same formation exposed in adjacent portions of Indiana represent an Ordovician shallow marine mud-bottom epeiric sea facies. These fine-grained elastics contain a moderately diverse mollusk-trilobite assemblage dominated by vagrant epifaunal detritus-feeding calymenid and asaphid trilobites, large endobyssate and infaunal filter-feeding pelecypods, and nektonic nautiloids. Articulate brachiopods, ectoprocts, and pelmatozoan echinoderms form only minor elements of this fauna.This mollusk-trilobite assemblage was common in Late Ordovician shallow marine clastic environments where mobility was an asset and there was an abundance of oxygen and food resources. Such assemblages are characteristic of the Lorraine Fauna of Late Ordovician (Edenian to Richmondian) age that occurs from the Ohio Valley north and east into New York, Ontario, Quebec, and Ireland. These early Paleozoic mud-bottom assemblages were considerably modified by the Late Ordovician extinction event and were replaced in the Silurian and Devonian by distinctly different assemblages dominated by large epifaunal strophomenid and spiriferid brachiopods, crinoids, and phacopid trilobites.

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