Scientists Just Found a Fossil That Doesn’t Belong to Any Known Life Form—What Is It?

A bizarre 400-million-year-old fossil may not be a plant, animal, or even a fungus. Known as Prototaxites, this extinct organism has confounded scientists for over a century. Now, new study evidence suggests it could belong to a completely unknown lineage of life—one that flourished on early Earth before vanishing without a trace.

The First Giants To Walk The Land

Between 420 and 375 million years ago, during the Silurian and Devonian periods, Prototaxites dominated prehistoric landscapes. It formed towering, trunk-like structures reaching up to 8 meters in height and a full meter across—dwarfing the other land organisms of its time.

First unearthed in 1843, these fossils were initially thought to be the remains of rotting conifers. For decades, debate raged: were they plants, giant algae, or fungi?

In 2007, Kevin Boyce of Stanford University and colleagues leaned toward a fungal identity after analyzing the fossil’s carbon isotopes. Their conclusion: Prototaxites did not photosynthesize like plants, but rather absorbed carbon from organic material—much like fungi do.

Was This Prehistoric Giant Something Entirely New?

But the latest twist in the saga comes from a new preprint study led by Corentin Loron at the University of Edinburgh, focusing on the smaller species Prototaxites taiti, discovered in the Rhynie chert fossil bed in Scotland.

More tellingly, when they compared the fossil’s chemistry to that of true fungi found in the same site, the results were stark. Prototaxites lacked chitin, the molecule that forms fungal cell walls. Instead, it showed signs of lignin-like compounds, typically found in plants.

A Lineage That Fits Nowhere

Loron and colleagues described Prototaxites as forming large, multicellular structures composed of various types of tubes, containing complex biopolymers resembling lignin, and feeding on decaying organic matter. These three characteristics are not known to occur together in any modern life form.

Kevin Boyce, who helped push the fungal hypothesis in 2007, acknowledged the shift: “Given the phylogenetic information we have now, there is no good place to put Prototaxites in the fungal phylogeny,” he said.

“So maybe it is a fungus, but whether a fungus or something else entirely, it represents a novel experiment with complex multicellularity that is now extinct and does not share a multicellular common ancestor with anything alive today,” quoted New Scientist.

The idea that Earth once hosted large organisms that don’t fit into any of the current kingdoms of life adds a striking twist to the story of evolution. These “lost lineages” may hint at life’s untapped potential—and how much we have yet to discover.

Brett Summerell of the Botanic Gardens of Sydney added a note of caution. “There are too many unknowns to say it is a unique lineage at this stage,” he said.

He noted that assigning it to the fungal kingdom was always “somewhat nebulous,” particularly considering its massive size.

“The conclusion that it is a completely unknown eukaryote certainly creates an air of mystery and intrigue around it.”