For over a century, a peculiar fossil towering over ancient landscapes has puzzled scientists. Now, a groundbreaking discovery may finally explain why—or deepen the mystery even further.
A Fossil Unlike Any Other
A bizarre 400-million-year-old fossil might not belong to any known category of life—neither plant, animal, nor even fungus. Known as Prototaxites, this long-extinct organism has baffled researchers for generations.
Now, new findings suggest it could be part of an entirely unknown lineage of life—one that thrived on early Earth before vanishing without a trace.
The First Giants to Walk the Earth
Between 420 and 375 million years ago, during the Silurian and Devonian periods, Prototaxites dominated prehistoric landscapes. These towering, trunk-like structures grew up to 8 meters (26 feet) tall and 1 meter (3 feet) wide, dwarfing most other land organisms of their time.
First discovered in 1843, the fossils were initially thought to be decayed conifer remains. For decades, debates raged—was Prototaxites a plant, giant algae, or fungus?
In 2007, Stanford University’s Kevin Boyce and his team leaned toward the fungal hypothesis after analyzing the fossil’s carbon isotopes. Their conclusion? Prototaxites did not photosynthesize like plants but absorbed carbon from organic material, similar to fungi.
A Prehistoric Giant Unlike Anything We Know?
But the latest twist in the mystery comes from a new study led by Corentin Loron at the University of Edinburgh. The team examined Prototaxites taiti, a smaller species discovered in Scotland’s Rhynie Chert fossil deposits.
What stood out most was the fossil’s chemical composition. When compared to actual fungi found in the same region, the results were striking: Prototaxites lacked chitin, the key molecule that forms fungal cell walls. Instead, it showed signs of lignin-like compounds, which are typically found in plants.
A Life Form That Defies Classification
Loron and his colleagues described Prototaxites as forming large, multicellular structures made up of different types of tubes, containing complex biopolymers resembling lignin, and feeding on decaying organic matter. No known modern organism shares all three of these characteristics.
Kevin Boyce, who previously supported the fungal theory, acknowledged the shift:
"Based on the phylogenetic information we have now, there’s no clear place to position Prototaxites within the fungal tree of life," he said.
"It may be a fungus, but whether it is or isn’t, it represents an entirely new experiment in complex multicellularity—one that has disappeared and doesn’t share a multicellular ancestor with anything alive today," Boyce told New Scientist.
Not Quite Alien—But Close
The idea that Earth once hosted massive organisms that don’t fit into any existing kingdom of life adds a fascinating twist to evolutionary history. These “lost lineages” hint at life’s untapped potential—and how much we still have to learn.
Brett Summerell from the Sydney Botanic Gardens urged caution, noting, "There are too many unknowns at this stage to claim it belongs to a completely unique lineage."
He also pointed out that its classification within the fungal kingdom was always “somewhat murky”, especially given its enormous size.
"The conclusion that it’s an entirely unknown eukaryote certainly adds an air of mystery and intrigue," Summerell said.
One thing is certain—this ancient giant challenges our understanding of life’s history. Could there be more undiscovered life forms that defy classification? The search for answers continues.
