3D-Analysis of a non-planispiral ammonoid from the Hunsrück Slate: natural or pathological variation?
- Published
- Accepted
- Subject Areas
- Paleontology, Taxonomy
- Keywords
- epicole, pathology, computed tomography, Hederelloidea, Ammonoidea, epizoa, heteromorph, three-dimensional reconstruction, CT scan, intraspecific variation
- Copyright
- © 2016 Stilkerich et al.
- Licence
- This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, reproduction and adaptation in any medium and for any purpose provided that it is properly attributed. For attribution, the original author(s), title, publication source (PeerJ Preprints) and either DOI or URL of the article must be cited.
- Cite this article
- 2016. 3D-Analysis of a non-planispiral ammonoid from the Hunsrück Slate: natural or pathological variation? PeerJ Preprints 4:e2479v1 https://doi.org/10.7287/peerj.preprints.2479v1
Abstract
We herein examine the only known non-planispirally coiled early Devonian ammonoid, the holotype specimen of Ivoites opitzi, to investigate if the host was encrusted in vivo and if these sclerobionts were responsible for the trochospiral coiling observed on this unique specimen. To test if the presence of runner-like sclerobionts infested the historically collected specimen of Ivoites opitzi during its life, we used microCT to produce a three-dimensional model of the surface of the specimen. Our results indicate that sclerobionts grew across the outer rim (venter) on both sides of the ammonoid conch at exactly the location where the deviation from the planispiral was recognized, and where subsequent ammonoid growth would likely preclude encrustation. This indicates in vivo encrustation of the I. opitzi specimen, and represents the earliest documentation of the phenomenon. Further, this suggests that non-planispiral coiling in I. opitzi was pathologically induced and does not represent natural morphological variation in the species. Despite the observed anomalies in coiling, the specimen reached adulthood and retains important identifying morphological features, suggesting the ammonoid was minimally impacted by encrustation in life. As such, appointing a new type specimen – as suggested by some authors – for the species is not necessary. In addition, we identify the sclerobionts responsible for modifying the coiling of this specimen as hederelloids, a peculiar group of sclerobionts likely related to phoronids. Hederelloids in the Devonian are commonly found encrusting on fossils collected in moderately deep environments within the photic zone and are rarely documented in dysphotic and aphotic samples. This indicates that when the ammonoid was encrusted it lived within the euphotic zone and supports the latest interpretations of the Hunsrück Slate depositional environment.
Author Comment
This is a submission to PeerJ for review.
Supplemental Information
Video of the three-dimensional model of KGM 1983/147
Digital visualisation of the investigated ammonoid Ivoites schindewolfi (KGM 1983/147) showing sclerobionts on both flanks.