"Four hundred million years ago, Earth was a different planet. In its oceans, a time traveler from our present day would still have encountered a reasonably familiar environment; indeed, a great diversity of fish already existed there. On land, however, the landscape would have looked like something out of a science fiction movie. Although living organisms had already established themselves there—and the first higher plants had emerged—they would have reached no higher than our hips at most. Yet, rising from this sparse vegetation in many regions of the ancient Earth were phallic columns, perhaps gray, brown, or whitish in color. The largest specimens discovered to date were a good meter thick and more than eight meters tall. For over 50 million years—from the end of the Silurian period into the late Devonian—they were, by far, the largest living organisms on land.
Paleontologists have named this genus *Prototaxites*. Beyond that, however, they know very little about these organisms—not even where to place them within the tree of life. Following their discovery in 1857, they were initially believed to be primitive precursors of trees—a notion reflected in their name, which derives from *Taxus*, the Latin word for the yew tree. For over a century thereafter, they were regarded as relatives of algae, until 2001, when the American paleobotanist Francis Hueber presented a detailed analysis of the tubular structures that make up the *Prototaxites* columns. With this work, he convinced the majority of his colleagues that these organisms must, in fact, be fungi—a conclusion further bolstered in 2007, when isotopic analyses ruled out the algae hypothesis by demonstrating that *Prototaxites* did not perform photosynthesis.
Now, a new study published in *Science Advances* thoroughly challenges the hypothesis that *Prototaxites* must have been a fungus. A team of fourteen scientists led by Corentin Loron and Alexander Hetherington from the University of Edinburgh examined a fragment of a specimen belonging to the species *Prototaxites taiti* from the Rhynie Chert in Scotland. Chert is a rock composed of silicon dioxide—colloquially known as silica—a variety of which is the well-known flint. Near Rhynie in Aberdeenshire, it was deposited during the Early Devonian period—407 million years ago—in a valley teeming with hot springs and geysers. The organisms entombed within it were preserved in remarkable detail, a fact that has earned the Rhynie Chert considerable prominence in the field of paleobiology. It serves as a key site for studying the flora of the Early Devonian, but also preserves examples of some of the earliest harvestmen and springtails.
The *Prototaxites* specimen from Rhynie is comparatively tiny. The specimen under study measured 5.6 centimeters in diameter during its lifetime and has been preserved over a length of 6.9 centimeters. However, the details of its intricate network of tubes are preserved with exceptional clarity. Consequently, researchers utilizing modern microscopic techniques were able to demonstrate that its internal structure differs fundamentally from that of any known group of fungi. These findings are further bolstered by chemical evidence. The process of silicification also preserved original organic material, which could be analyzed spectroscopically and compared with fossilized remains of insects, plants, and fungi that coexisted with this *Prototaxites* specimen and are likewise preserved within the Rhynie Chert.
"Our analyses demonstrate that fossilization products derived from sugars and proteins are present in the chitinous organisms found within the Rhynie Chert—specifically in fungi and arthropods." "However, in *Prototaxites taiti*, these fossilization products are absent," the authors write. "The simplest interpretation is therefore that, during its lifetime, *P. taiti* did not possess a typical fungal cell wall composition—including chitin—which calls into question the interpretation that it was a fungus."
At the very least, they were not fungi that can be assigned to any of the groups known from later periods. Volker Wilde of the Senckenberg Society for Nature Research in Frankfurt shares this view. "Attempts were made to classify them based on certain anatomical features, and that seemed plausible enough at the time," says the paleobotanist. "But these new data actually argue against that."
Now, however, the researchers from Edinburgh go a step further, proposing that *Prototaxites* be assigned to a completely different type of multicellular life—specifically, to a separate taxonomic kingdom alongside those of animals, plants, and fungi. "Claiming this on such a basis is indeed somewhat speculative—and perhaps a bit sensationalist," observes Volker Wilde. "After all, we do not know what level of diversity the groups we are familiar with—such as fungi, for instance—possessed during that era. It certainly cannot be ruled out that organisms belonging to the fungal kingdom had a different metabolism and synthesized different materials than modern-day fungi."
Nor is *Prototaxites* the only instance of a fossilized life form whose taxonomic classification remains unclear even at the level of biological kingdoms. For a number of forms within the Ediacara biota—whose representatives appear as the earliest complex macroscopic organisms, predating the Cambrian explosion of species 539 million years ago—an assignment to the animal kingdom is more than questionable. Yet even from much later periods, there are still cases that taxonomists can only classify as *incertae sedis*—of uncertain placement (within the tree of life)—albeit none of such spectacular dimensions as *Prototaxites*. Volker Wilde, for instance, studies the fossil remains of a leaf-like life form named *Nematothallus*, also dating from the Early Devonian. "They occur alongside *Prototaxites* remains—and nobody knows where those belong, either." [1]
1. Phallisch im Erdaltertum: Von wegen Pilze: Einer der rätselhaftesten Organismen der Erdgeschichte ist noch ein ganzes Stück rätselhafter geworden. Frankfurter Allgemeine Zeitung; Frankfurt. 28 Jan 2026: N2. ULF VON RAUCHHAUPT
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