26-Foot-Tall Giant ‘Fungi-Like' Organism Might Be A Lost Form Of Life — A Biologist Explains

Forbes

07-04-2025

Prototaxites, a towering organism that once dominated the barren landscapes of early terrestrial Earth 440 to 360 million years ago, has long been an enigma among paleobiologists.
For nearly two centuries, its true identity eluded scientists, as fossilized remains revealed a structure that defied classification. Its colossal, branchless trunks were a puzzle, hinting at a lost chapter in the history of life on this planet.
The first fossils of Prototaxites were unearthed in the mid-19th century, sparking debates over whether they were the remnants of ancient conifers or peculiar forms of algae.
As research progressed, the scale and unique anatomy of these fossils gradually steered scientists toward a fungal interpretation. Yet, as new analytical techniques emerged, the simplicity of earlier interpretations was challenged.
Today, fresh evidence suggests that Prototaxites might represent an entirely novel branch of life, one that no longer exists in our modern world.
The story of Prototaxites begins with its discovery in 1843, when paleontologists first stumbled upon giant, cylindrical fossils along the ancient riverbanks of Gaspé Bay in Quebec, Canada.
Early interpretations by scientists such as John William Dawson initially identified these massive trunks as decayed conifer remnants. However, the absence of typical conifer anatomy quickly cast doubt on this idea.
Subsequent studies revealed a complex internal structure — an interwoven network of narrow tubes with diameters as small as 50 micrometers. This internal architecture featured a variety of tube types: some thick and unbranched, others thin with intricate, branching networks, suggesting an alternative origin.
Physiologically, Prototaxites was unlike any organism known today. Its towering form — it could reach heights of up to 26 feet and stretch a meter wide — dwarfed other Devonian flora such as Cooksonia (see image below) and indicates that they likely played a critical ecological role in early terrestrial ecosystems.
Furthermore, the variable carbon isotopic ratios found in its tissues supported the idea that it did not rely on photosynthesis but instead derived carbon from a mix of substrates — a characteristic trait of heterotrophic organisms that cannot produce their own food.
Thus, for much of the 20th century, the prevailing view among scientists was that Prototaxites was a giant fungus. Early microscopic examinations by researchers like Arthur Church in 1919, coupled with subsequent work by Francis Hueber in 2001, solidified the notion that these fossils were the fruiting bodies of an enormous fungal organism.
Chemical analyses in 2007 by teams including C. Kevin Boyce provided further support by revealing carbon isotope ratios characteristic of heterotrophic fungi. However, the classification was never without controversy.
Over the years, debates raged as further evidence complicated the picture. Prototaxites lacked key biochemical markers found in all known fungi, most notably, traces of chitin in their cell walls.
While some researchers attempted to reconcile these differences by suggesting that Prototaxites might be a giant lichen (a symbiotic association between fungi and photosynthetic partners), other studies instead pointed to its entirely distinct molecular fingerprint.
Repeated reclassifications have demonstrated that traditional fungal taxonomy could not fully accommodate the unique features of Prototaxites. In effect, while early work grouped it with Ascomycota, later discoveries forced scientists to consider whether it represented a lost lineage that defies the modern fungal framework altogether.
The most recent breakthrough in our understanding of Prototaxites comes from a yet-to-be peer-reviewed study focused on a species designated as Prototaxites taiti, and investigated by a team from the University of Edinburgh.
These scientists re-examined exquisitely preserved specimens from the famed Rhynie chert — a deposit known for its exceptional fossil quality from the early Devonian period.
Their in-depth analysis combined advanced imaging techniques, such as confocal laser scanning microscopy and Fourier-transform infrared spectroscopy, with machine learning algorithms trained to recognize molecular fingerprints of known organisms.
What emerged was startling: P. taiti exhibited internal tube structures with subtle annular thickenings, along with medullary spots that did not match the reproductive or structural elements found in modern fungi.
The chemical analysis further showed a complete lack of chitin while revealing the presence of unusual lignin-like compounds. These findings led the researchers to conclude that P. taiti could not be comfortably placed within any existing branch of the eukaryotic tree, be it fungi, plants, or animals.
Fungi or animal? Not possible due to the lack of chitin and the structure of the cell walls. A plant or algae? Very unlikely considering what we know about its chemical composition. A lichen? Its anatomy indicates otherwise.
Instead, it appears to represent an entirely novel form of multicellular life — a lineage that evolved complex structures and a unique heterotrophic lifestyle before disappearing without a trace, leaving us to wonder about what now seems like a missing branch of the tree of life.
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