Nimbosphaera Rothwellii Nov. Gen. et Sp., an Enigmatic Microfossil Enveloped in a Prominent Sheath from the Lower Devonian Windyfield Chert, Scotland

Abstract

Premise of research. Microbial mats in the Lower Devonian Windyfield chert comprise diverse communities of organisms; however, little information on the various life forms that occur in these formations is available. A recently cut and thin-sectioned block of Windyfield chert contains an extensive microbial mat that formed among an in situ stand of charophytes.Methodology. Thin sections of the chert were screened systematically at high magnification (×400 and ×1000) in transmitted light. Images of fossils were captured digitally and processed in Adobe Photoshop CS6.Pivotal results. The microbial mat contains 15 specimens of Nimbosphaera rothwellii nov. gen. et sp., a hitherto unknown microfossil composed of a vesicle containing spheroidal bodies and enveloped in a prominent sheath. Extending from some vesicles are a bulbous appendage and putative rhizoids. The fossils resemble the sheathed zoosporangia of certain extant chytrids, in particular Rhizophydium coronum, thus suggesting affinities of N. rothwellii to Chytridiomycota.Conclusions. This discovery expands our knowledge of the diversity of organisms that thrived in early nonmarine microbial mats and provides further evidence that microbial mat frameworks served as a conservation trap for delicate microbial life in the Rhynie and Windyfield settings.