Rhizoliths and the Recognition of Plant and Microbial Trace Fossils

Recognizing a trace fossil as a record of organism–substrate interaction is well agreed upon, but some organisms and some interactions are not considered by some workers to be tracemakers or to have produced trace fossils. This is particularly the case with sedimentary structures created or modified by plants and micro-organisms. Plant-made structures that some workers have identified as trace fossils are phytoliths, leaf galls, borings/corrosion structures and rhizoliths. Only borings/corrosion structures and rhizoliths are generally agreed to be trace fossils. Phytoliths are not trace fossils, and most workers do not consider leaf galls to be traces, though that conclusion is open to question. Microbialites (both stromatolites and microbially induced sedimentary structures [MISS]) are not generally regarded as trace fossils, but identification of them as trace fossils has increased recently. The ichnotaxonomy of trace fossils made by plants and MISS needs to be regulated by the Botanical and Prokaryote Codes of Nomenclature. The specific recognition of ichnofossils and the procedures for their ichnotaxonomy need to be spelled out in those codes, much as they have been for animal trace fossils in the Zoological Code. Studies of modern roots and of rhizoliths provide a robust ichnotaxobase for their ichnotaxonomy, including shape, surface texture, internal structures, size, branching, orientation and substrate. Using that ichnotaxobase, a new ichnotaxon, Syrinxichnus tanneri igen. nov and isp. nov., is proposed for some Triassic rhizoliths.