For an epoch spanning over 165 years, a singular ancient entity that emerged from Earth’s nascent terrestrial expanses has eluded precise categorization. Known by the binomial moniker Prototaxites, this colossal, pillar-like organism flourished on land more than 400 million years prior to the advent of arboreal life, attaining vertical dimensions that reached as high as 8 meters (26 feet). A recent investigation spearheaded by paleontologists affiliated with the University of Edinburgh and National Museums Scotland posits that this profoundly enigmatic entity was not, contrary to prevailing scientific consensus, a gigantic fungal form, but rather represented an ancestral branch of complex life that has since vanished from the planet.
Prototaxites was the largest organism on land 410 million years ago. Image credit: Matt Humpage.
Prototaxites stands as Earth’s inaugural colossal inhabitant of the dry land, making its appearance during the Late Silurian and Devonian geological periods, approximately 420 to 370 million years ago.
Identified through its distinctive columnar fossilized remains, capable of extending up to 8 meters in length, it exerted dominion over early terrestrial ecosystems well before the evolutionary emergence of trees.
This organism, prevalent across ancient extraterrestrial environments and seemingly a food source for arthropods, occupied a crucial ecological niche during a transformative era in the terrestrial colonization process.
Notwithstanding over 165 years of dedicated scientific scrutiny, its fundamental biological classification has remained a subject of ongoing debate, with paleontologists divided on whether it constituted a fungal entity or belonged to a distinct, now entirely extinct, evolutionary lineage of sophisticated eukaryotic organisms.
The recent research undertaken by Dr. Corentin Loron and his collaborators centered on Prototaxites taiti, a specific species preserved with remarkable three-dimensional fidelity within the 407-million-year-old Rhynie chert formation located in Aberdeenshire, Scotland.
“The Rhynie chert is an exceptional scientific resource,” remarked Dr. Loron, the principal author of the investigation, which was disseminated this week in the esteemed journal Science Advances.
“It represents one of the planet’s most ancient fossilized terrestrial ecosystems. The superior quality of its preservation, coupled with the sheer diversity of life forms it encapsulates, empowers us to pioneer innovative methodologies, such as the application of machine learning to analyze fossil molecular data.”
“Furthermore, an extensive repository of other specimens from the Rhynie chert already resides within museum collections, facilitating comparative analyses that can substantially enrich scientific findings and provide critical context.”
The research team meticulously examined a novel specimen of Prototaxites taiti—which is the most substantial example of this species unearthed from the locality to date—thereby enabling in-depth anatomical and molecular comparisons with fossilized fungi discovered within the same geological strata.
Microscopic examination revealed an intricate internal structural organization that radically deviates from that observed in any known fungal species.
The fossil specimen is constituted by three discernible types of tubular structures, inclusive of expansive, robust-walled tubes exhibiting annular striations and dense, spherical formations designated as medullary spots.
These unique spots are composed of intricate, three-dimensional networks of interconnected tubes, a branching architecture that the scientists contend holds no precedent within the realm of fungal biology.
Employing infrared spectroscopy in conjunction with a machine-learning-driven classification system, the study’s authors juxtaposed the molecular signature of Prototaxites against that of fossilized fungi, arthropods, plant life, and bacteria recoverable from the Rhynie chert.
Fungal fossils originating from this site consistently exhibit characteristic chemical markers indicative of chitin-rich cellular walls. However, these specific markers were notably absent in the Prototaxites specimens.
The research group also undertook a search for perylene, a substance identified as a biomarker associated with pigment compounds synthesized by certain fungal species and previously identified in other Rhynie chert fossils. This particular compound was not detected in the analyzed Prototaxites samples.
Collectively, the structural, chemical, and biomarker evidence strongly refutes the hypothesis that Prototaxites was affiliated with any fungal group, including either basal or stem relatives of contemporary fungi.
“It is profoundly exhilarating to achieve a significant advancement in resolving the protracted debate surrounding Prototaxites, a discussion that has persisted for approximately 165 years,” stated Dr. Sandy Hetherington, the senior author of the publication.
“These organisms were indeed alive, but in a form vastly different from any currently recognized life. They exhibit distinct anatomical and chemical characteristics that set them apart from both fungal and plant life, thereby signifying their origin from an entirely extinct evolutionary branch of the tree of life.”
“Our research, which synergistically integrates an analysis of the fossil’s chemistry and anatomy, conclusively demonstrates that Prototaxites cannot be subsumed within the fungal classification,” affirmed Laura Cooper, a co-author of the paper.
“Given that prior researchers have already excluded Prototaxites from other categories of large, complex life forms, our deduction is that Prototaxites belonged to a separate and now wholly extinct lineage of complex organisms.”
“Consequently, Prototaxites exemplifies an independent evolutionary trajectory undertaken by life in its endeavor to construct large, intricate organisms—an undertaking about which we can only gain knowledge through the study of exceptionally preserved fossil evidence.”
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Corentin C. Loron et al. 2026. Prototaxites fossils are structurally and chemically distinct from extinct and extant Fungi. Science Advances 12 (4); doi: 10.1126/sciadv.aec6277
