DOI: 10.5061/dryad.msbcc2g30
title: Preservational modes of some ichthyosaur soft tissues (Reptilia, Ichthyopterygia) from the Jurassic Posidonia Shale of Germany

description: Konservat-Lagerstätten, such as the Toarcian (Early Jurassic) Posidonia
 Shale of southwestern Germany, are renowned for their spectacular fossils.
 Ichthyosaur skeletons recovered from this formation are frequently
 associated with soft-tissues; however, the preserved material ranges from
 three-dimensional, predominantly phosphatized structures to dark films of
 mainly organic matter. We examined soft-tissue residues obtained from two
 ichthyosaur specimens using an integrated ultrastructural and geochemical
 approach. Our analyses revealed that the superficially-looking ‘films’ in
 fact comprise sections of densely aggregated melanosome (pigment)
 organelles sandwiched between phosphatized layers containing fibrous
 microstructures. We interpret this distinct layering as representing
 condensed and incompletely degraded integument from both sides of the
 animal. When compared against previously documented ichthyosaur fossils,
 it becomes readily apparent that a range of preservational modes exists
 between presumed ‘phosphatic’ and ‘carbonized’ soft-tissue remains. Some
 specimens show high structural fidelity (e.g., distinct integumentary
 layering), while others, including the fossils examined in this study,
 retain few original anatomical details. This diversity of soft-tissue
 preservational modes among Posidonia Shale ichthyosaurs offers a unique
 opportunity to examine different biostratinomic, taphonomic, and
 diagenetic variables that potentially could affect the process of
 fossilization. Soft-tissue preservation in the Posidonia Shale likely was
 regulated by a multitude of factors, including decay efficacy and speed of
 phosphatic mineral nucleation; these in turn were governed by a seafloor
 with sustained microbial mat activity fuelled by high organic matter input
 and seasonally fluctuating oxygen levels.
description: <em><strong>Photography and light
 microscopy </strong></em>
 Photographs of fossils were
 taken with a Pentax WG-III camera. Both untreated
 and demineralized
 fossil samples were examined under an Olympus SZX16 microscope
 equipped with an Olympus SC30 digital camera. 
 <em><strong>Transmission electron microscopy
 (TEM) </strong></em> Demineralized fossil matter
 was dehydrated in ethanol
 and then stepwise embedded in epoxy resin/ethanol mixtures, with the last
 step being pure epoxy. Embedded samples were allowed to polymerize at room
 temperature for 72 hrs and then placed in an oven at 60˚C for 48 hrs. Thin
 sections were made using a Leica EM UC7 ultramicrotome. A glass knife was
 used to produce semi-thin (200 nm) sections for initial quality control.
 Ultrathin (50 nm) sections were subsequently prepared using a diamond
 knife, and the sections were then mounted on pioloform-coated copper
 grids. TEM images were acquired using a JEOL JEM-1400 PLUS instrument at
 80 and 120 kV with a bottom-mounted Matataki CMOS camera at the Department
 of Biology, Lund University, Sweden.
 <em><strong>Synchrotron rapid-scanning X-ray fluorescence
 (SRS-XRF)</strong></em>
 X-ray fluorescence was
 conducted at beamline 10-2, Stanford Synchrotron Radiation Lightsource,
 USA. Incident X-ray energy was set to 11 keV using a Si (111)
 double-crystal monochromator with the Stanford Position Electron
 Accelerating Ring storage ring containing 500 mA at 3.0 GeV. Fluorescence
 lines of the targeted elements and the intensity of the total scattered
 X-rays were observed using a silicon drift Vortex detector (SII
 NanoTechnology). A focused 100 × 100 μm beam was filtered through a 100
 μm Ta pinhole aperture. Incident and transmitted
 X-ray intensities were measured with nitrogen-filled ion chambers, with
 the incident X-ray flux measured at around 8 × 10<sup>10</sup> ph/s. The fossils
 were mounted on a vertically oriented aluminium bracket at 45˚ relative to
 the incident X-ray beam. The fluorescence detector was mounted at 90˚ in
 relation to the incident beam and was held at a distance of ~4 cm from the
 specimens at ambient atmospheric conditions. Data were collected by
 spatially rastering the X-ray beam over the mounted fossils as the stage
 was in continuous motion. Fluorescence signal was gated by an encoder
 signal at pixel sizes of 100 or 200 μm with beam exposure time at 20 ms
 per pixel. Image and data processing were completed on Sam’s Microprobe
 Analysis Toolkit (SMAK; Webb 2011).
description: Sam's Microprobe Analysis Toolkit (SMAK) for raw XRF
 Data