DOI: 10.5061/dryad.8cz8w9gz4
title: Exploring the preservation of a parasitic trace in decapod crustaceans using finite elements analysis

description: The fossil record of parasitism is poorly understood, due largely to the
 scarcity of strong fossil evidence of parasites. Understanding the
 dynamics of preservation for fossil parasitic evidence is critical to
 contextualizing the fossil record of parasitism. Here, we present the
 first use of X-ray computed tomography (CT) scanning and finite elements
 analysis (FEA) to analyze the impact of a parasite-induced fossil trace on
 host preservation. Seven fossil and modern decapod crustacean specimens
 with branchial swellings attributed to an epicaridean isopod parasite were
 CT scanned and examined with FEA to assess differences in the magnitude
 and distribution of stress between normal and swollen branchial chambers.
 The results of the FEA show highly localized stress peaks in reaction to
 point forces, with higher peak stress on the swollen branchial chamber for
 all specimens, suggesting a possible shape-related decrease in the
 preservation potential of these parasitic swellings. Broader application
 of these methods as well as advances in the application of 3D data
 analysis in paleontology are critical to understanding the fossil record
 of parasitism and other poorly represented fossil groups.
description: <strong>Specimen acquisition</strong>
             Seven specimens of recent and fossil decapod
 crustacean specimens with swellings attributable to <em>K.
 crusta</em> were studied through institutional loans: three Recent
 specimens of <em>Munida valida</em> from the Gulf of Mexico
 preserved in 70% ethanol (Fig 1 A-C), three complete fossil specimens of
 <em>Macroacaena rosenkrantzi</em> in siderite concretions from
 the Maastrichtian of Greenland, from a site referred to as the
 oyster-ammonite locality (Fig 1 D-F), and one isolated fossil carapace of
 <em>Panopeus nanus</em> in lower Miocene limestone from the
 Duncans Quarry, Trelawny Parish, Jamaica (FLMNH-IP locality XJ015) (Fig 1
 G). These specimens were studied through institutional loans from Texas
 A&M University in College Station, Texas, USA (TAMU), the Natural
 History Museum of Denmark in Copenhagen, Denmark (NHMD) stored in the Type
 and Illustrated Paleontology Collection, and the University of Florida,
 Florida Museum of Natural History, Invertebrate Paleontology in
 Gainesville, Florida, USA (UF-FLMNH-IP), respectively. The recent
 specimens of <em>Munida valida</em> are corpses, the fossil
 specimens of <em>Macroacaena rosenkrantzi </em>likely
 represent corpses, and the fossil specimen of <em>Panopeus nanus
 </em>likely represents a molt. Each specimen has one swollen
 branchial chamber, in either the left (n=3), or right (n=4) chamber. No
 permits were required for the described study, which complied with all
 relevant regulations. <strong>Scanning and CT
 data preparation</strong>         CT data was
 initially processed and visualized using the NSI efX software and was then
 exported as TIFF images stacks for further preparation. The image stacks
 output was imported into the software Dragonfly ORS 2022.1 for
 visualization and 3D conversion of the CT data. The specimens were
 segmented from the raw data using a mixture of manual segmentation and
 manually trained AI-assisted segmentation models. Segmented specimen data
 was rendered for visualization in Dragonfly, then exported as
 Stereolithography (STL) 3D models. Specimen STLs were imported into the
 software Blender 3.4 for additional cleaning and processing, including the
 removal of unconnected elements, remeshing, downscaling, and fixing
 geometry errors. After cleaning and fixing errors, each model was
 standardized to a uniform size and to a uniform number of faces
 (20,000±1,000) to improve the comparability of results between
 specimens. <strong>Finite elements
 analysis</strong>           The prepared specimen
 3D models were imported into the software FreeCAD 0.20.2 and converted
 into FEA models using the program Gmsh 4.11.1. In FreeCAD, identical
 material properties were applied to each model, which were amalgamated
 from multiple studies of the material properties of decapod skeletal
 elements. The ventral surfaces of the specimens were set as constraints,
 and a force of ten newtons of point load force was applied at
 perpendicular angles to faces at the same location on both the left and
 right branchial chamber of each specimen (for each specimen, this included
 one normal branchial chamber and one swollen branchial chamber). The
 finite elements analysis was solved using the solver CalculiX 2.10, then
 the results were exported into Paraview 5.11.0 as Visualization Toolkit
 (VTK) files for observation and visualization of FEA results. Von Mises
 stress, which described the stress response of a given material relative
 to the limit at which the material deforms, was chosen as the primary FEA
 output metric for characterizing the stress, strain, and deformation of
 the models in response to a force. The vertex data from the left and right
 sides of each mesh were isolated from each other to compare von Mises
 stress values between the normal and swollen sides of each
 specimen.
description: # Exploring the preservation of a parasitic trace in decapod crustaceans
 using finite elements analysis
 [https://doi.org/10.5061/dryad.8cz8w9gz4](https://doi.org/10.5061/dryad.8cz8w9gz4) ## Description of the data and file structure The associated CSV file contains unordered von Mises stress values associated with vertices from finite elements analysis performed on healthy and swollen (ichnotaxon *Kanthyloma crusta*) branchial chambers of CT-scanned fossil and modern decapod crustaceans. See dataset and dataset description for information about the specimens. All values are von Mises stress in pascals. For more information, see the associated article.