DOI: 10.5061/dryad.rxwdbrvfn
title: Data from: Gilsonicaris from the Lower Devonian Hunsrück Slate is a eunicidan annelid and not the oldest crown anostracan crustacean

description: The Lower Devonian (Lower Emsian, -400 Myr) roof slates of the Hunsrück in
 southeastern Germany have delivered a highly diverse and exceptionally
 preserved marine fauna that provides a unique snapshot into the anatomy
 and ecology of a wide range of Palaeozoic animals. Several of the
 described taxa, however, remain enigmatic in their affinity, at least
 until new pyritized features hidden under the surface of the slate are
 revealed using X-ray radiography or micro-computed tomography (µCT). Here
 we redescribe such an enigmatic fossil, the putative anostracan
 crustacean Gilsonicaris rhenanus Van Straelen, 1943. Using µCT
 scanning, we unveil unprecedented details of its anatomy, including a
 ventral oral opening and four pairs of recalcitrant jaw elements. These
 jaws are morphologically consistent with the scolecodonts of eunicidan
 polychaetes, which along with the gross anatomy of the body and head
 unambiguously identifies G. rhenanus as a polychaete rather than an
 arthropod. While this discovery firmly discards the Early Devonian record
 of crown anostracans in the fossil record, it adds a new record of
 eunicidan soft tissues, which are surprisingly rare considering the
 abundant microfossil record of scolecodonts.
description: X-ray radiography of the slate
 and local micro-computed tomography (µCT) of <em>Gilsonicaris
 rhenanus</em> Van Straelen, 1943 (accession number IRSNB
 a11647) were performed at the AST-RX imaging platform of the Muséum
 national d’Histoire naturelle (Paris, France), using a GE Sensing and an
 Inspection Technologies phoenix | x-ray v | tome | ×L240-180 CT scanner.
 µCT
 scanning was limited to the articulated anterior part of the specimen,
 which also allowed for achieving higher resolution. 2600 projections were collected
 over 214° to account for
 the extremely flat nature of the specimen, using 3 averaged images per projection, 1 second
 of exposure time, and 1 skipped image before each projection. Voltage and
 current were set to 90 kV and 300 mA, respectively. The volume was
 reconstructed using the phoenix datos| xfi 2.0 reconstruction software,
 yielding an isotropic voxel size of 10.15 µm. The tomographic dataset was
 then exported into an
 8-bit TIFF image stack of 48 coronal slices (the dataset –29 MB– is
 available on Morphosource;
 https://www.morphosource.org/concern/media/000523565). Segmentation and 3D rendering were performed using the software MIMICS Innovation Suite 19.0 (Materialise) at the IPANEMA laboratory. Automatic thresholding and manual selection were used for the segmentation of the cuticle and mouthparts, respectively. 3D models are available on Sketchfab (https://skfb.ly/ow8w7 and https://skfb.ly/ow8xH). We also assessed qualitatively µCT-derived density differences between the different materials present in the fossil using ImageJ, by extracting greyvalue histograms from areas of interest using the Freehand selection tool. The data are shown in Electronic supplementary material (ESM) figure S1 of the paper, but we provide in this Data Repository the histogram data and R script used to produce this figure.
description: Follow the R script
 "Gueriau-etal-Gilsonicaris_R-script.r" to load the histograms
 and generate the plot presented in figure S1i of the paper. This script
 opens data from the Excel file
 "Gueriau-etal-Gilsonicaris_histograms.xlsx". It includes at the
 beginning all needed libraries/packages needed to load and plot the
 histograms, which need to be installed prior to running the script.
 Comments throughout the script should make its use
 straightforward.