Data from: Wide gape in the Ordovician brachiopod Rafinesquina explains how unattached filter-feeding strophomenoids thrived on muddy substrates
Data files
May 28, 2024 version files 6.97 GB
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Dattilo_et_al_Supplemental_Data.zip
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README.md
Abstract
Strophomenoid brachiopods had thin, concavo-convex shells, were ubiquitous colonisers of Paleozoic muddy seafloors, and are hypothesised 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 3-D 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 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 also hint that other strophomenoids with similar interarea angles lived with their shells widely agape.
README
Images of figured specimens, exploratory scans, and cross-sections
These data are a suite of high resolution photographs of specimens (Figs. 2, 5, 11A, 11I), scans and models of serially sectioned specimens (Figs. 6, 9, 10, 13), SEM images (Figs. 11B, 11C), and hinge tracings (Fig. 11DE).
Description of the data and file structure
Files are organized in nested folders and tied to the figures, with both raw and edited versions of images included. Folders include:
Fig02_CMC98738: High resolution, uncropped image of Rafinesquina specimen CMC IP98738, on the upper surface of a shell-sand bed from Brookville, Indiana, USA. CMC=Cincinnati Museum Center. Scale bars are 1 mm
Fig05AB_CMC98739: High resolution, uncropped, unlabeled images of Rafinesquina specimen CMC IP98739, including three close-ups of the hinge area. Scale bars are 1 mm.
Fig05CD_CMC98740: High resolution, uncropped, unlabeled image of Rafinesquina specimen CMC IP98740. Scale bars are 1 mm.
Fig06_CMC51999-3: High resolution, uncropped, unlabeled image of Rafinesquina specimen CMC IP51999-3 in matrix, from Stonelick Creek, Ohio, USA. Scale bars are 1 mm. Also included is a folder ("Peels") with transmitted light photomicrographs of the peels taken approximately every 3 mm, showing sequential cross-sectional views through the sample, and a folder with scans of the slabbed cross-sections ("Slices") through the same sample.
Fig09_CMC98737: Three folders are included, that contain scans of the slabbed cross-sections ("scans") through Rafinesquina specimen CMC IP98737 from Manchester, Indiana, USA, tracings of the valves derived from these sections ("Tracings"), and exploratory models ("3D files") used to assess the potential articulation of the valves.
Fig10_CMC98741: Five folders are included of data pertaining to Rafinesquina specimen CMC IP98741 from Orangeburg Road, Kentucky, USA, including folders that contain transmitted light photomicrographs of the peels ("Peels") taken approximately every 0.5 mm, scans of the slabbed cross-sections ("Aligned Scans"), tracings of the pedicle valve ("AlignedPed") and brachial valve ("AlignedBrach") derived from these data, and exploratory models ("3D models") used to assess the potential articulation of the valves
Fig11A_CMC98742: High resolution, uncropped, unlabeled images of ventral valve of Rafinesquina specimen CMC IP98742 from Orangeburg Road, Kentucky, USA, including three close-ups of the hinge area. Scale bars are 1 mm.
Fig11B_CMC98743: Additional SEM images of silicified ventral valve of Rafinesquina specimen CMC IP98743 from USGS locality 7812-CO, Cynthiana, Kentucky, USA.
Fig11C_CMC98744: Additional SEM images of silicified dorsal valve of Rafinesquina specimen CMC IP98744 from USGS locality 7812-CO, Cynthiana, Kentucky, USA.
Fig11DE_CMC98745_CMC98746: Five folders are included of data pertaining to Rafinesquina specimen CMC IP98745 and CMC IP98756 from USGS locality 7812-CO, Cynthiana, Kentucky, USA, including folders that contain high resolution images of the two valves, with muscle scars highlighted ("080416 muscle trace"), high resolution images of the hinge area with hinge elements highlighted ("080419 Hinge Parts"), and images showing exploratory realignment of the valves in different modes of articulation ("080419 In Articulated Positions").
Fig11I_CMC98747: High resolution images of articulated silicified Rafinesquina specimen CMC IP98747 from USGS locality 7812-CO, Cynthiana, Kentucky, USA, including close-ups of the interarea, dental plate and associated features.
Fig13_CMC98748: Five folders are included of data pertaining to Rafinesquina specimen CMC IP98748 from St Catherine, Kentucky, USA, including folders that contain scans of the slabbed cross-sections ("SliceScansAligned") of the specimen, tracings of the pedicle valve ("SliceTrace Pedicle") and brachial valve ("SliceTraceBrachial") derived from these sections, exploratory models ("3D files") used to assess the potential articulation of the valves, and photographs of the printed models ("PhotosPrintedModel") in different degrees of valve opening.
Methods
We employed a range of techniques for the analysis of the hinge morphology and function of Rafinesquina. We began with examination under a reflected light microscope, also documenting specimens by macrophotography, microphotography, and SEM imaging of the interiors of disarticulated valves with special attention to the articulating features of the hingeline and the distribution of muscle scars in the interior of the shells. We studied silicified Rafinesquina valves in the same way. Specimens from the large USGS collections of isolated valves were useful for comparing the features on opposing valves of similar size, as well as testing for fit. However, isolated valves do not always fit well even if similar in size because they did not come from the same individual. These specimens are also delicate. High resolution illustrations of all figured specimens in different orientations, as well as some of the exploratory scans and cross-sections used in this study, are available in this Dryad data set.
Small silicified specimens are often articulated, and we examined a suite of such articulated specimens visually and scanned them using a SkyScan 1172 X-ray microCT. 3D models of these specimens were examined to gain insights into hinge articulation and those data are available in MorphoSource. Because such specimens had between-valve silicification that could not always be distinguished from shell material, we mainly used these analyses to guide our approaches for serial sectioning and interpreting unsilicified specimens.
The most useful results were obtained through serial sectioning and serial grinding of articulated specimens, whereby we generated a series of sagittal sections through each brachiopod. We employed a slice spacing of ~3 mm in initial work, and based on those results decreased our slice spacing to ~0.5 mm. One 3D model based on serial sectioning work is presented herein, illustrated by different articulations of an oversize printed model. Slices from this work also permitted analysis of the function of each section in two dimensions and calculation of the centre of mass at different gapes. For mass calculations, when density is uniform, the centre of mass is equal to the centre of volume. Volumetric centres were computed before and after remeshing the model to a voxel size of 0.4 mm to smoothly interpolate between slices. Table S1 shows that remeshing did not substantially alter the computed volume. The centre of volume of the valves was calculated with gape angles of 0° (closed), 20°, and 45°, to compute how gape alters the distribution of mass for the highest density component of the living brachiopods - the shell. Additional methodological information is in Appendix S1.