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The mid-Paleozoic was punctuated by a rapid radiation of durophagous (shell-crushing) predators. These new predators were primarily placoderm and chondrichthyan fishes but probably also included phyllocarid and eumalacostracan arthropods. Coincident with the radiation of these durophages, beginning in the mid-Devonian, there was an increase in the frequency of predation-resistant morphologies in a variety of marine invertebrate taxa. Among bellerophontid molluscs, disjunct coiling disappeared and umbilici became less common while the frequency of genera with sculpture increased. The abundance of brachiopod genera with spines on one or both valves increased dramatically. Sculpture became more pronounced and common among genera of coiled nautiloids. Inadunate and camerate crinoids showed a marked increase in spinosity, and all three crinoid subclasses tended to develop thicker thecal plates.Trends toward increasing relative frequencies of predation-resistant features were formed in different ways. Bellerophontid genera lacking predation-resistant features tended to go extinct, leaving the sculptured, tighdy coiled forms as the predominant forms. Among Brachiopoda, the radiation of productids provided the tremendous increase in numbers of spinose genera. Among crinoids, predation-resistant features were acquired through evolution within established clades.These observations suggest that predation by shell-crushing predators has been an important control on the morphology and composition of the marine invertebrate fauna since at least the Middle Devonian. The mid-Paleozoic radiation of durophages and response of the marine fauna was in many respects similar to events of the Mesozoic Marine Revolution, in effect, the Paleozoic precursor to that event.

Cramer, B.D., Brett, C.E., Melchin, M.J., Männik, P., Kleffner, M.A., McLaughlin, P.I., Loydell, D.K., Munnecke, A., Jeppsson, L., Corradini, C., Brunton, F.R. & Saltzman, M.R. 2011: Revised correlation of Silurian Provincial Series of North America with global and regional chronostratigraphic units and δ13Ccarb chemostratigraphy. Lethaia, Vol. 44, pp. 185–202. Recent revisions to the biostratigraphic and chronostratigraphic assignment of strata from the type area of the Niagaran Provincial Series (a regional chronostratigraphic unit) have demonstrated the need to revise the chronostratigraphic correlation of the Silurian System of North America. Recently, the working group to restudy the base of the Wenlock Series has developed an extremely high‐resolution global chronostratigraphy for the Telychian and Sheinwoodian stages by integrating graptolite and conodont biostratigraphy with carbonate carbon isotope (δ13Ccarb) chemostratigraphy. This improved global chronostratigraphy has required such significant chronostratigraphic revisions to the North American succession that much of the Silurian System in North America is currently in a state of flux and needs further refinement. This report serves as an update of the progress on recalibrating the global chronostratigraphic correlation of North American Provincial Series and Stage boundaries in their type area. The revised North American classification is correlated with global series and stages as well as regional classifications used in the United Kingdom, the East Baltic, Australia, China, the Barrandian, and Altaj. Twenty‐four potential stage slices, based primarily on graptolite and conodont zones and correlated to the global series and stages, are illustrated alongside a new composite δ13Ccarb curve for the Silurian. Conodont, graptolite, isotope, New York, Ontario, series, Silurian, stage.

Abstract. Integrated geochemical data suggest that black shale deposition in the Devonian Geneseo Formation of western New York was initiated by the coincidence of siliciclastic starvation and the intensification of seasonal water column stratification and mixing. Once established, however, black shale deposition was maintained through efficient recycling of biolimiting nutrients which enhanced primary productivity. Recycling efficiency was achieved through a positive feedback loop of oscillating benthic redox conditions that enhanced N and P regeneration from sediments, sustained high primary productivity by returning nutrients to the photic zone during mixing, and ensured a downward flux of organic matter that drove or enhanced the episodic development of benthic anoxia during stratification. This feedback was ultimately disrupted by rising siliciclastic influx, which diluted organic matter and restored benthic redox stability. The abrupt overturn of diverse, long-standing Appalachian basin marine communities may have been the result of trophic resource destabilization during Geneseo deposition.

Taphonomic study of echinoderms provides useful information on sedimentary conditions before, during, and after burial. Taphonomic studies of Recent echinoderms indicate that much skeletal disarticulation occurs within a few days after death. However, experiments also indicate that within a short period after death echinoderm carcasses remain rather resistant to disarticulation, and thus may be transported a considerable distance by currents; following periods of a few hours of decay, more delicate portions of echinoderm skeletons are readily disarticulated. Some skeletal modules (e.g., crinoid pluricolumnals) may resist disarticulation for periods of months in quiet- and or cool-water environments. Anoxia promotes intact preservation by excluding scavenging metazoans. Echinoderm ossicles may undergo minor abrasion and/or corrosion if left exposed, and less dense stereom corrodes much more rapidly than dense plates, such as echinoid spines. However, heavily abraded ossicles may indicate prefossilization and reworking.Various groups of echinoderms (e.g., pelmatozoans, asterozoans, echinoids) have differing propensities for degradation and, therefore, produce different arrays of preserved fossil material primarily depending upon the relative rates of burial, bottom-water oxygenation, and turbulence. Echinoderms may be divided into three groups based upon the relative ease of skeletal disarticulation. Type 1 echinoderms include weakly articulated forms (e.g., asteroids and ophiuroids) that rapidly disintegrate into individual ossicles. Type 2 includes those echinoderms whose bodies contain portions in which are more tightly sutured, as well as portions in which the ossicles are somewhat more delicately bound (e.g., crinoids, regular echinoids). Such echinoderms display more varied taphonomic grades from fully intact to mixtures of isolated ossicles and articulated modules. Type 3 comprises those echinoderms (e.g., irregular echinoids) in which major portions of the skeleton are so resistant to disarticulation that they may be broken across sutures rather than coming apart at plate boundaries.Comparative taphonomy of particular types of echinoderm skeletal remains leads to recognition of distinctive taphofacies that characterize particular depositional environments. Taphofacies include two types of characteristic modes of fossil preservation: event taphonomic signatures and background taphonomic signatures. Depending upon normal conditions of environmental energy and rates of sedimentation, the background condition of various types of echinoderms for a given facies may range from articulated, unabraded skeletal modules (in Types 2 and 3) to highly corroded and/or abraded ossicles. Conversely, the occurrence of fully intact fossil echinoderms provides unambiguous evidence of rapid and deep burial of benthic communities. Such well-preserved fossil assemblages can provide a wealth of information regarding the paleobiology of echinoderms, as well as the nature of the depositional events and burial histories.This paper presents a preliminary classification and characterization of background and event aspects of echinoderm taphofacies for carbonate- (9 taphofacies, including reefs and hardgrounds) and siliciclastic-dominated (5 taphofacies) environments. In each case, we recognize a spectrum of echinoderm taphofacies that coincides with a gradient of environments, ranging from nearshore, high energy shoreface through proximal and distal storm-influenced shelf, to deeper ramp and dysoxic basinal settings. Most taphofacies also feature particular styles of obrution (smothered bottom) Lagerstätten. These range from scattered lenses of articulated fossils in some high energy sandstone and grainstone facies to bedding planes of articulated, pyrite coated specimens in dark shales. We classify and discuss the genesis of these types of Lagerstätten and list typical examples. Finally, we present a simple model that integrates the occurrence of various echinoderm taphofacies with concepts of cyclic and sequence stratigraphy.