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Scientists baffled at mysterious ancient creature that doesn't fit on the tree of life as we know it:

A bizarre ancient life-form, considered to be the first giant organism to live on land, may belong to a totally unknown branch of the tree of life, scientists say.

These organisms were massive, with some species growing up to 26 feet (8 meters) tall and 3 feet (1 m) wide. Named Prototaxites, they lived around 420 million to 375 million years ago during the Devonian period and resembled branchless, cylindrical tree trunks.

Since the first Prototaxites fossil was discovered in 1843, scientists haven't been sure whether they were a plant, fungus or even a type of algae. However, chemical analyses of Prototaxites fossils in 2007 suggested they were likely a giant ancient fungus.

Now, according to a study published Wednesday (Jan. 21) in the journal Science Advances, Prototaxites might not have been a humongous fungus after all — rather, it may have been an entirely different and previously unknown — and now extinct — life-form.

"They are life, but not as we now know it, displaying anatomical and chemical characteristics distinct from fungal or plant life, and therefore belonging to an entirely extinct evolutionary branch of life," study lead co-author Sandy Hetherington, a research associate at the National Museums Scotland and senior lecturer from the School of Biological Sciences at the University of Edinburgh, said in a statement.

All life on Earth is classified within three domains — bacteria, archaea and eukarya — with eukarya containing all multicellular organisms within the four kingdoms of fungi, animals, plants and protists. Bacteria and archaea contain only single-celled organisms.

[...] However, according to this new research, Prototaxites may actually have been part of a totally different kingdom of life, separate from fungi, plants, animals and protists.

[...] Upon examining the internal structure of the fossilized Prototaxites, the researchers found that its interior was made up of a series of tubes, similar to those within a fungus. But these tubes branched off and reconnected in ways very unlike those seen in modern fungi.

"We report that fossils of Prototaxites taiti from the 407-million-year-old Rhynie chert were chemically distinct from contemporaneous Fungi and structurally distinct from all known Fungi," the researchers wrote in the study. "This finding casts doubt upon the fungal affinity of Prototaxites, instead suggesting that this enigmatic organism is best assigned to an entirely extinct eukaryotic lineage."

[...] Kevin Boyce, a professor at Stanford University, led the 2007 study that posited Prototaxites is a giant fungus and was not involved in this new research. However, he told New Scientist that he agreed with the study's findings.

"Given the phylogenetic information we have now, there is no good place to put Prototaxites in the fungal phylogeny," Boyce 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."

Journal Reference: Corentin C. Loron, Laura M. Cooper, Seán F. Jordan, et al., Prototaxites fossils are structurally and chemically distinct from extinct and extant Fungi, Science Advances, 21 Jan 2026, Vol 12, Issue 4 DOI: 10.1126/sciadv.aec6277

Original Submission