Prototaxites fossils are structurally and chemically distinct from extinct and extant Fungi

Loron, C.C., Cooper, L.M., McMahon, S., Jordan, S.F., Gromov, A.V., Humpage, M., Rodgers, N., Pichevin, L., Vondracek, H., Alexander, R., Dzul, E.R., Brasier, A.T., Krings, M., and Hetherington, A.J.

by Dipika Mishra, Akiyoshi Lab

Prototaxites were the first giant terrestrial organisms to inhabit Earth’s surface, with their columnar fossils occurring from the late Silurian to the early Devonian (420 to 370 million years ago). Evidence suggests that Prototaxites played a crucial role during the process of terrestrialization. However, despite their ecological significance, the systematic affinity of this group has remained debatable. While some researchers describe Prototaxites as a fungus, it has also been suggested that it is a member of an extinct lineage. 

To gain further insights into the systematic position of Prototaxites, researchers at the Hetherington lab at the University of Edinburgh have re-examined the fossils of Prototaxites taiti, a well-preserved specimen from the Early Devonian Rhynie chert. The researchers performed biomarker analysis to detect perylene, a known biomarker for phytopathogenic fungi, and found that perylene was absent in the samples. Prototaxites taiti samples also lack chitin which is a common component of the fungal cell wall. Furthermore, Prototaxites also differ anatomically from fungi in the tube branching patterns and the presence of abundant banded tubes. Thus, using microscopy and molecular analysis, the researchers have identified that Prototaxites are not only chemically distinct from contemporary fungi but also structurally distinct from all known fungi. Consequently, in the absence of a fungal affinity, the researchers have suggested that Prototaxites should be placed within a previously undescribed extinct eukaryotic lineage, and have thus provide a new perspective on the long-standing conundrum regarding the systematic position of Prototaxites.

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