DOI: 10.5061/dryad.cjsxksn2w
title: Data from: A new Devonian euthycarcinoid evidences the use of different respiratory strategies during the marine-to-terrestrial transition in the myriapod lineage

description: Myriapods were, together with arachnids, the earliest animals to occupy
 terrestrial ecosystems, by at least the Silurian. The origin of myriapods
 and their land colonization have long remained puzzling until
 euthycarcinoids, an extinct group of aquatic arthropods considered
 amphibious, were shown to be stem group myriapods, extending the lineage
 to the Cambrian and evidencing a marine-to-terrestrial transition.
 Although possible respiratory structures comparable to the air-breathing
 tracheal system of myriapods are visible in several euthycarcinoids,
 little is known about the mechanism by which they respired. Here we
 describe a new euthycarcinoid from Upper Devonian alluvio-lagoonal
 deposits of Belgium. Synchrotron-based elemental x-ray analyses were used
 to extract all available information from the only known specimen. Sulfur
 x-ray fluorescence (XRF) mapping and spectroscopy unveil sulphate
 evaporation stains, spread over the entire slab, suggestive of a very
 shallow-water to terrestrial environment prior to burial consistent with
 an amphibious lifestyle. Trace metal XRF mapping reveals a pair of ventral
 spherical cavities or chambers on the second post-abdominal segment that
 do not compare to any known feature in aquatic arthropods, but might well
 play a part in air-breathing. Our data provide additional support for
 amphibious lifestyle in euthycarcinoids and show that different
 respiratory strategies were used during the marine-to-terrestrial
 transition in the myriapod lineage.
description: Data were collected at wiggler beamline 6-2 of the Stanford
 Synchrotron Radiation Lightsource (SSRL). The diameter of the incoming
 X-ray beam was reduced to 50 µm using a tantalum pinhole. The fossil was
 mounted on an xy scanner stage allowing ±50 cm movements relative to the
 x-ray beam, but with micrometric accuracy. X-ray fluoresced photons were
 collected using a single element X-ray fluorescence Vortex silicon drift
 detector placed in the horizontal plane. The present
 dataset includes 3 types of data: <strong>(1)
 Synchrotron Rapid Scanning X-Ray Fluorescence (SRS-XRF) elemental
 maps</strong> Methods:
 Integrated intensities in preselected spectral regions corresponding to
 the emission lines of elements of interest were recorded on the fly in the
 horizontal direction at a pixel rate corresponding to a scan distance of
 50 µm per ~4 ms. Distributions of Ca, Mn, Fe, Ni, Cu, Zn, Ga, As, Br
 (Kα<sub>1</sub>) and Pb (Lβ<sub>1</sub>) emission
 lines were mapped using an incident beam energy of 13.5 keV. Distributions
 of Al, Si, P, S and Cl Kα<sub>1</sub> emission lines were
 mapped using an incident beam energy of 3.15 keV while the fossil was
 enclosed within a custom-built helium purged chamber to reduce scattering
 and absorption of the incident and fluoresced low energy X-rays by air. In
 the paper, all elemental distributions presented (figures 2, S1, S2) are
 displayed using a linear grey scale going from white (low abundance) to
 black (high abundance), normalized between the 10<sup>th</sup>
 and 90<sup>th</sup> percentiles (except for the S map,
 slightly saturated to better reveal S associated to the fossil).
 Data:
 figure2bce-S1a-DATA_XRF-map-As-TextImage.txt;
 figure2f-DATA_XRF-map-Mn-TextImage.txt;
 figure2g-S2-DATA_XRF-map-S-TextImage.txt;
 figureS2-DATA_XRF-map-Ca-TextImage.txt;
 figureS2-DATA_XRF-map-Cu-TextImage.txt;
 figureS2-DATA_XRF-map-Fe-TextImage.txt;
 figureS2-DATA_XRF-map-Ga-TextImage.txt;
 figureS2-DATA_XRF-map-Ni-TextImage.txt;
 figureS2-DATA_XRF-map-Zn-TextImage.txt.
 <strong>(2) Full XRF spectra</strong>
 Methods: In the same conditions, a few full
 XRF spectra were additionally collected in several points of interest with
 a 30 s count time. Element contributions were assessed through fitting
 using the PyMCA data-analysis software, and the resulting
 'configuration files' are provided here.
 Data: figureS1b-DATA_XRF-spectrum-cuticle.mca;
 figureS1c-DATA_XRF-spectrum-matrix.mca.
 Processing Files:
 figureS1b-PROC_XRF-spectrum-cuticle-PyMCA-FitConfigFile;
 figureS1c-PROC_XRF-spectrum-matrix-PyMCA-FitConfigFile.
 <strong>(3) X-ray Absorption Near Edge Structure (XANES)
 spectroscopy at the S K-edge</strong>
 Methods: S XANES spectra were collected in
 fluorescence mode in the 2450–2550 eV range with energy steps of 1 eV
 between 2450 and 2460 eV, 0.25 eV between 2460 and 2490 eV, and 1 eV
 between 2490 and 2550 eV. The count time was set to 0.5 s per energy step.
 ZnSO<sub>4</sub> (prepared as a pellet) was used for energy
 calibration by setting the position of the main resonance (i.e. sulphate
 peak) at 2481.75 eV. Data: The three
 spectra shown in the paper (figure 2h) are gathered in the following Excel
 spreadsheet: figure2h-DATA_S-K-edge-spectra.xlsx.
description: <strong>(1) Synchrotron Rapid Scanning X-Ray Fluorescence
 (SRS-XRF) maps:</strong> How to
 use: These .txt maps are text images that can  easily be open
 using the freeware ImageJ (&gt;File &gt;Import &gt;Text
 image...). <strong>(2) Full XRF
 spectra</strong> How to use:
 The .mca data files can be open as any text file, but we suggest here to
 use the PyMCA data-analysis freeware for which we provide the fitting
 'configuration files' as used in the paper (figure
 S2b,c). <strong>(3) X-ray Absorption Near Edge
 Structure (XANES) spectroscopy at the S K-edge</strong>
 How to use: The provided spreadsheet can be
 opened easily with Excel or equivalent. Raw spectra are already displayed,
 and the spreadsheet includes all other acquisition parameters required for
 further data processing.