This Bizarre Fossil Isn't a Plant, Animal, or Fungus—Turns Out It's a Whole New Form of Life

Yahoo

26-03-2025

Prototaxites, an extinct organism from the Devonian period, has been thought to be a fungus since its first fossil was unearthed.
Analysis of one Prototaxites species showed that its physical and chemical characteristics were not only different from those of any existing fungus—the didn't match any existing organism at all.
Prototaxites is now thought to belong to an extinct group of eukaryotes, but what exactly that group was remains a mystery.
430 million years ago, towering life-forms known as Prototaxites emerged from the ground, reaching heights of up to 26 feet and growing trunks up to 3 feet wide. When the first Prototaxites fossil was unearthed in 1843, it was mistaken for an ancient rotting conifer. But trees didn't yet exist during the Silurian period, so what exactly was this thing taking over the ancient supercontinent of Gondwana?
That argument was never truly settled. Most scientists made Prototaxites out to be a sort of humungous fungus, but the field as a whole was never certain. That, however, may have just changed.
Back in 2007, the carbon isotopes in fossils convinced scientists this really was a fungus, since they appeared to be evidence that Prototaxites behaved like fungi by leeching off other living organisms for oxygen. Videos with clickbait titles like When Giant Fungi Ruled the Earth soon spread through the internet. But now, a new analysis by researchers at the University of Edinburgh is showing otherwise.
When paleobiologist Corentin Loron and his colleagues examined Prototaxites fossils from what is now Aberdeenshire, Scotland, they found evidence that it was anatomically and chemically differed from fungi in too many ways to be considered fungal. The problem—it also belonged with nothing else. It was apparently not a plant, animal, or fungus.
'Having found no support for the most widely held view that Prototaxites was fungal, we next reviewed possible placement in other higher taxonomic groups. No extant group was found to exhibit all the defining features of Prototaxites,' they said in a study recently uploaded to the preprint server bioarXiv.
The specimens that Loron studied were of the species Prototaxites taiti—smaller than the behemoths found elsewhere, but still preserved well enough to take a closer look at their external and internal structures. Tubes on the side of one of the specimens had been previously determined to be sacs filled with spores, which is why that group of researchers placed the species at the base of the extinct fungal group Ascomycota. Loron's team found, however, that this supposedly fertile part has no organic connection to the rest of the organism.
Petrified slices of P. taiti had a light brown exterior and dark brown medullary spots (blobs of cells that were arranged irregularly) on the inside. Existing fungi do not have medullary spots. Its innards were also made up of all sorts of tubes, including thin tubes that bent and branched, larger curving tubes with thicker walls but no branches, and even larger unbranched tubes with faint structures similar to growth rings. No extant fungi have tubes like this inside them—let alone with strange rings. The only place rings are found in fungi are in spore sacs known as elaters.
Prototaxites only got weirder after its chemical analysis. If it really was a fungus, then the cell walls of P. taiti should show remains of certain sugars that resulted from the taphonomic breakdown of chitin—a strong, fibrous substance also found in the shells of crustaceans and exoskeletons of insects. However, there were no traces of these sugars found in P. taiti. While the researchers are open to the possibility that some sugars and proteins could have been lost in the early phases of fossilization, it is unlikely, as there were plenty of chemicals found in the fossilized soil of the region in which this species of Prototaxites grew.
'No extant group was found to exhibit all the defining features of Prototaxites,' Loron said in the study, suggesting that 'it is best considered a member of a previously undescribed, entirely extinct group of eukaryotes.'
Maybe Prototaxites was a fun guy if you got to know him, but he just didn't fit in with the fungi.
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