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Strophomenoid brachiopods had thin, concavo‐convex shells, were ubiquitous colonizers of Palaeozoic muddy seafloors, and are hypothesized to have filter‐fed in a concave‐upward orientation. This orientation would elevate their line of commissure out of potentially lethal lophophore‐clogging mud. The paradox is that epibiont distributions on strophomenoids support a convex‐upward life position, as do studies of strophomenoid stability and trace fossils formed by strophomenoid sediment‐clearing. A premise of the concave‐upward orientation hypothesis is a narrow gape, which causes narrow, high velocity inhalant currents, leaving strophomenoids vulnerable to sediment entrainment. Herein we investigate the gape angle of Rafinesquina using serial thin sections and peels, silicified specimens, computer modelling, SEM analysis, x‐ray microCT, and 3D printing. Hinge line structure suggests that, conservatively, Rafinesquina could gape 40–45°. Such a gape occurred when diductor muscle contraction could not cause any further rotation, hinge teeth and crenulations were disengaged, and interareas interlocked. In contrast, when closed, hinge teeth were locked in hinge sockets. This wide gape eliminates constraints on feeding orientation. In either convex‐up or concave‐up orientation, Rafinesquina could feed with slow, diffuse inhalant currents incapable of disturbing sediment, and could snap valves shut to forcefully expel enough water to clear sediment from the mantle cavity, explaining previously described moat‐shaped trace fossils associated with shells. Our findings demonstrate that Rafinesquina gaped at an angle approximately equal to the angle between the two interareas when the valves are closed. Our analyses hint that other strophomenoids with similar interarea angles also lived with their shells widely agape. [ABSTRACT FROM AUTHOR]

Polyfocal photography is a method for obtaining digital images that have great depth of focus. A series of photos are made at successive focal levels from the bottom to the top of a fossil using reflected light. Computer software takes the part of each image that is in focus and merges all of the parts into a composite image that is entirely in focus. Microscopes designed for this purpose are available but are expensive. A petrographic microscope with a digital camera can produce such a series of images, and they can be composited by an inexpensive computer program. Polyfocal photography appears to be superior to other methods of photography for illustrating conodonts. Composite images show internal features, such as basal cavities and white matter, and the software can convert one composite image into a stereoscopic pair. [ABSTRACT FROM AUTHOR]

The Upper Ordovician Cincinnatian Series is a critical upper Katian reference succession. Previously, six 3rd-order depositional sequences (C1 to C6) have been recognized and frequently used as regional time slices. Recent research, however, indicates a need for revision and additions, including the recognition of additional 3rd- and 4th-order sequences. We propose amendments based upon high-resolution correlations using a combination of regional disconformities, cycle stacking patterns, bioevents, marker beds, and chemostratigraphy. Several disconformities, including a large regionally angular mid-Richmondian unconformity, are newly recognized or reinterpreted. In addition, distinctive depositional patterns aid in the recognition of systems tracts, with a) thick proximal laminated peritidal facies representing early transgressive systems tracts (TSTs) or lowstands, in part (LSTs), b) shell-rich limestone packages representing later TSTs and overlain by c) more shale-prone highstand systems tracts (HSTs), themselves overlain locally by d) siliciclastic dominated falling stage systems tract (FSST) deposits that are commonly removed beneath substantial unconformities (sequence boundaries). At present, we recognize eight 3rd-order Cincinnatian sequences, designated C1 through C8, and 16 4th-order subdivisions and their component systems tracts. A younger (Hirnantian?) sequence may be present at some localities as the enigmatic Centerville Formation and/or basal Belfast Member of the Brassfield Formation. The implications of these new correlations and sequence interpretations include a new standard for relative sea-level changes and insights into basin dynamics. This framework also permits a more nuanced history of biotic changes that include geologically brief pulses of immigration associated with the transgressions of the C1 (lower Kope Formation), C5C (Clarksville Member of Waynesville Formation), and C7A (basal Whitewater Formation). • Synthesis of Upper Ordovician (Cincinnatian) litho- and biofacies patterns • Revised model of cratonic, mixed siliciclastic‑carbonate sequences presented • Existing sequence stratigraphic framework for the Cincinnatian is strongly revised. • New framework recognizes 8 third-order and more than 16 fourth order sequences. • Provides new insights into temporal patterns of physical and biotic events [ABSTRACT FROM AUTHOR]