Triskelia scotlandica , an enigmatic Rhynie chert microfossil revisited

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RESEARCH PAPER

Triskelia scotlandica, an enigmatic Rhynie chert microfossil revisited Michael Krings1,2,3  Received: 26 August 2020 / Accepted: 30 September 2020 © Paläontologische Gesellschaft 2020

Abstract The enigmatic microfossil Triskelia scotlandica from the Lower Devonian Rhynie chert is an acritarch-like, usually spheroidal to ovoid vesicle with a surface ornamentation comprised of isolated triradiate and meandering, high membranous ridges. The form has been formally described based on dispersed specimens preserved inside the remains of a land plant axis, and interpreted as the resting stage of a microscopic alga. Unusual microbial coatings on land plant axes from the Rhynie chert have recently yielded > 300 additional specimens of T. scotlandica, many of which occur in situ in prominent swellings of fungal hyphae. This discovery is a strong evidence that T. scotlandica is not algal, but rather fungal or fungus-like in nature. The swellings might be oogonia of a representative of the Oomycota (e.g., Saprolegniales), and T. scotlandica accordingly an ornamented oospore. However, specimens with a discharge tube suggest that T. scotlandica is more likely a zoosporangium or resting spore stage of an endoparasite, perhaps with affinities to the holocarpic Oomycota (e.g., Olpidiopsis), Cryptomycota (e.g., Rozella), or zoosporic fungi (e.g., Olpidium), in which case the hyphal swellings would be either dilatations resulting from the expansion of the parasite inside, or a host response (hypertrophy). The affinity of T. scotlandica remains unresolved, due in part to the uncertain diagnostic value of the surface ornamentation, and because no other stages of the life history of this organism are known. Nevertheless, the new specimens expand our knowledge of the microbial interactions that existed in early terrestrial ecosystems. Keywords  Devonian · Fungi · Hypertrophy · Microbial coating · Oomycota · Parasitism · Preservation · Surface ornamentation

Introduction The Early Devonian Rhynie chert Lagerstätte (including the Rhynie and Windyfield chert sites) in Aberdeenshire, Scotland, yields comprehensive information on the morphology, internal organization, and biology of early non-marine aquatic and terrestrial plants, animals, and microorganisms, Handling Editor: Mike Reich. * Michael Krings [email protected] 1



SNSB-Bayerische Staatssammlung für Paläontologie und Geologie, Richard‑Wagner‑Straße 10, 80333 Munich, Germany

2



Department für Geo‑ und Umweltwissenschaften, Paläontologie und Geobiologie, Ludwig-Maximilians-Univer sität, Richard‑Wagner‑Straße 10, 80333 Munich, Germany

3

Department of Ecology and Evolutionary Biology, Natural History Museum and Biodiversity Institute, University of Kansas, Lawrence, KS 66045‑7534, USA



notably fungi (Krings et al. 2017a; Trewin and Kerp 2017; Garwood et al. 2020). Many Rhynie chert fossils also contain direct evidence of organismal interactions and provide insights into the ecological roles certain organisms played in the environments in which they lived (Taylor