For over 165 years, the enigmatic prototaxite has stood as one of the earliest giants to rise from Earth’s barren landscapes, defying simple classification. These towering, columnar organisms dominated the terrestrial environment over 400 million years ago, reaching impressive heights of 8 meters (26 ft), long before the advent of trees. A recent study conducted by paleontologists from the University of Edinburgh and the National Museums of Scotland posits that this mysterious entity was not merely a giant fungus, as often presumed, but rather belonged to an entirely extinct lineage of complex life.
Prototaxites dominated terrestrial ecosystems 410 million years ago as the largest living organisms. Image credit: Matt Humpage.
The prototaxite marks the first giant life form on Earth’s surface, emerging during the late Silurian to late Devonian periods, approximately 420 to 370 million years ago.
Recognized for their pillar-like fossils that can reach up to 8 meters, they played a crucial role in early terrestrial ecosystems well before the emergence of trees.
These organisms were widely distributed across ancient terrestrial environments and were likely consumed by arthropods, marking a pivotal stage in land colonization and holding significant ecological importance.
Despite over 165 years of inquiry, the biological identity of prototaxite remains a topic of heated debate among paleontologists, who contest whether it is a fungus or belonged to a distinct, entirely extinct lineage of complex eukaryotes.
In a groundbreaking study, Dr. Corentin Rollon and colleagues examined Prototaxites Taichi, found preserved in remarkable three-dimensional detail within the 407-million-year-old Rhynie Chert in Aberdeenshire, Scotland.
“The Rhynie Chert is a remarkable treasure trove,” noted Dr. Rollon, the lead author of the study published in this week’s edition of Scientific Progress.
“This site represents one of the oldest fossilized terrestrial ecosystems, and its well-preserved biodiversity enables innovative approaches like machine learning applied to fossil molecular data.”
“Numerous other specimens from the Rhynie Chert are preserved in museum collections, contributing vital context to our findings.”
The research team investigated new specimens of Prototaxites Taichi, identifying the largest known example of this species at the site, facilitating detailed anatomical and molecular comparisons with fossil fungi found in the same deposits.
Microscopic imaging revealed a complex internal structure that diverges significantly from any known fungi.
The fossil comprises three distinct types of tubes, including large, thick-walled tubes featuring annular stripes and dense spherical regions known as medullary points.
These intriguing features form a complex 3D network of interconnected tubes, suggesting a branching pattern unheard of in fungal biology.
Researchers employed infrared spectroscopy and machine learning techniques to classify molecular fingerprints from prototaxite alongside those of fossil fungi, arthropods, plants, and bacteria found in Rhynie Chert.
Fossilized fungi from this location maintain characteristic chemical signatures linked to chitin-rich cell walls, which were intriguingly absent in ancient prototaxite.
The team also searched for perylene, a biomarker associated with pigment compounds produced by specific fungi, previously detected in other Rhynie Chert fossils. However, no such compounds were found in the prototaxite sample.
Collectively, the structural, chemical, and biomarker findings imply that prototaxite does not align with any known fungal group, including the earliest forms of modern fungi.
“This research marks a significant advancement in a 165-year-long discussion,” stated Dr. Sandy Hetherington, the senior author of the paper.
“These organisms represent life forms distinct from those we currently recognize, displaying different anatomical and chemical characteristics from fungi and plants, thereby belonging to a unique, now-extinct lineage of complex life.”
“Our study combines chemical analysis and anatomical insights into prototaxite, revealing that it cannot be classified within any known fungal group,” explained co-author Laura Cooper.
“As earlier researchers have discounted classifications to other large and complex life forms, we conclude that prototaxite belonged to an entirely distinct lineage of extinct complex life.”
“Thus, prototaxite symbolizes independent evolutionary experiments in constructing large and complex organisms, known to us only through exceptionally preserved fossils.”
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Corentin C. Rollon et al. 2026. Prototaxites fossils are structurally and chemically distinct from both extinct and extant fungi. Scientific Progress 12(4); doi: 10.1126/sciadv.aec6277
