Prototaxites, which was long believed to be a giant fungus, is fascinating researchers. The researchers are now proposing that it may instead belong to a completely unknown branch of life. Discovered in 1843 within the Rhynie chert of Scotland, these fossils date back to the Devonian period, approximately 420 to 375 million years ago. Prototaxites resembled enormous tree trunks and achieved incredible dimensions. Some species grew as high as 26 feet (8 m) tall and spread as wide as 3 feet (1 m).
This unusual anatomy has been the basis of a long-standing and heated dispute over the taxonomic affinity of Prototaxites. At first, scientists thought it was a huge mushroom. This idea received a high-profile boost from a 2007 chemical analysis that found striking parallels to the oldest known fungi. On the inside, it contained a complex framework of tubes like those found in mushrooms. It left out chitin, the most important component of fungal cell walls. These findings have prompted scientists to revise its origin and classification.
Based on isotopic signatures, Prototaxites fossils had a chemical signature that differs significantly from what we know fungi to have. Some researchers have suggested that Prototaxites was never a fungal organism at all and does not belong in any phylogeny of fungi.
“Given the phylogenetic information we have now, there is no good place to put Prototaxites in the fungal phylogeny,” – Kevin Boyce
This startling finding has fueled the idea that Prototaxites was an entirely new experiment in complex multicellularity. Strikingly, like no organism known to have survived today, it could come from a wholly extinct, non-aquatic lineage.
The recent identification of lignin-like polymer precursor chemicals inside extant and Prototaxites biomineralized fossils complicate this picture. Compounding this is the fact that lignin is most commonly found in the woody tissue and bark of plants, which makes its classification as fungal even muddier. Despite this association, Prototaxites was probably feeding on decaying organisms, a characteristic of fungi that many species still possess.
“We conclude that the morphology and molecular fingerprint of P. taiti is clearly distinct from that of the fungi and other organism preserved alongside it in the Rhynie chert, and we suggest that it is best considered a member of a previously undescribed, entirely extinct group of eukaryotes,” – Researchers
The mystery behind Prototaxites is deepened by the fact that it is by far the largest organism in the Rhynie ecosystem. Its anatomical characteristics are radically different from living and extinct fungi.
“We report that Prototaxites taiti was the largest organism in the Rhynie ecosystem and its anatomy was fundamentally distinct from all known extant or extinct fungi,” – Researchers
That Prototaxites could be something entirely unimagined in the eukaryotic realm, not to mention on planets elsewhere in the galaxy, raises the already-enigmatic organism’s coolness factor.
“The conclusion that it is a completely unknown eukaryote certainly creates an air of mystery and intrigue around it — probably not likely to be solved until more fossils are discovered or new analytical techniques developed,” – Brett Summerell
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