Arm waving in stylophoran echinoderms: three-dimensional mobility analysis illuminates cornute locomotion

Abstract

The locomotion strategies of fossil invertebrates are typically interpreted on the basis of morphological descriptions. However, it has been shown that homologous structures with disparate morphologies in extant invertebrates do not necessarily correlate with differences in their locomotory capability. Here, we present a new methodology for analysing locomotion in fossil invertebrates with a rigid skeleton through an investigation of a cornute stylophoran, an extinct fossil echinoderm with enigmatic morphology that has made its mode of locomotion difficult to reconstruct. We determined the range of motion of a stylophoran arm based on digitized three-dimensional morphology of an early Ordovician form, Phyllocystis crassimarginata . Our analysis showed that efficient arm-forward epifaunal locomotion based on dorsoventral movements, as previously hypothesized for cornute stylophorans, was not possible for this taxon; locomotion driven primarily by lateral movement of the proximal aulacophore was more likely. Three-dimensional digital modelling provides an objective and rigorous methodology for illuminating the movement capabilities and locomotion strategies of fossil invertebrates.

Moving legs: A workflow on how to generate a flexible endopod of the 518 million‐year‐old Chengjiang arthropodErcaicunia multinodosausing3D‐kinematics (Cambrian, China)

“…However, this has to be conducted differently from the approaches in analyzing Chengjiang arthropods, that is, grinding the fossil to certain pieces, and hereafter digitalization and surface reconstruction. Ordovician echinoderms may be another group appropriate to μCT analyses as well as kinematic Maya approaches (see Clark et al, 2020). Nonetheless, the preservation of Chengjiang fossils (Gabbott et al, 2004) makes them eminently suitable for μCT analyses, surface reconstructions, and mobility simulations.…”

“…We use the program Maya 2020 (Autodesk Inc., San Rafael, CA) combined with the add‐on X_ROMM tools (X‐ray reconstruction of moving morphology; Brainerd et al, 2010). Maya has been used for more than 10 years (Kushwaha, 2015; Wood, 2014, 2015) and has already been applied to anatomical and kinematic studies of extant (Baier & Gatesy, 2013; Dawson, Metzger, Baier, & Brainerd, 2011; Kambic, Roberts, & Gatesy, 2015; Krings, Nyakatura, Fischer, & Wagner, 2014) and extinct (Nyakatura et al, 2015; Nyakatura et al, 2019) vertebrates, and even for fossil invertebrates (Clark, Hutchinson, Bishop, & Briggs, 2020). We report Maya analyses for the first time analyzing Cambrian arthropods.…”

Three-dimensional visualization as a tool for interpreting locomotion strategies in ophiuroids from the Devonian Hunsrück Slate

“…Three-dimensional digital imaging is the only non-destructive strategy currently available that allows simultaneous visualization of the three-dimensional geometry of the skeletal elements of fossil ophiuroids and their relative positioning in situ . This information is a necessary basis for biomechanical inferences such as the geometry of the joint interfaces and the range of motion [ 31 , 42 ]. Application of the methodology outlined here to a broad scope of Palaeozoic ophiuroids with opposing and fused ambulacrals (such as Eospondylus [ 11 ]) is necessary to illuminate the evolutionary history and ecological context of the rise to dominance of musculoskeletally-driven locomotion in brittle stars.…”

“…Careful airbrasive preparation with iron powder retains spectacular detail, but does not reveal the specimen in the round [ 32 , 38 ]. As micro-CT imaging illuminates density contrasts, this technique is a useful tool for visualizing fossil specimens where there is a strong density differential between the material comprising the fossil and the surrounding matrix, or where preservation is mouldic [ 42 ]. In the case of the Hunsrück Slate, three-dimensional image processing tools can be used for the digital removal of the slate matrix from the pyritized fossils ( figure 1 ).…”

Molecular Paleobiology of the Echinoderm Skeleton

“…From a palaeontological perspective, the CaCO3 skeleton of echinoderms has provided most members of the phylum Echinodermata with an exceptional fossil record (Figure 1). This has facilitated their use to understand morphological, paleoecological, and trait-based evolution across long and deep time scales (Wright, 2017, Hopkins and Smith, 2015, Cole et al, 2019, Deline et al, 2020, Mongiardino Koch and Thompson, 2020b, Bauer, 2020, Syverson and Baumiller, 2014, Clark et al, 2020. In addition to this rich insight into paleobiological questions, the echinoderm skeleton is also a cutting-edge model system used to understand how the regulation, function, and expression of genes, directs the processes of animal development and evolution (Shashikant et al, 2018, Davidson et al, 2002a, Revilla-i-Domingo et al, 2007, Oliveri et al, 2008, Dylus et al, 2018.…”