Plant, animal or fungus? A mysterious ancient life form may rewrite our understanding of evolution

An ancient life form that lived around 420 million years ago fundamentally challenges everything we think we know about evolution and the classification of species. The organism known as Prototaxites, which could grow up to eight metres tall, was neither a plant, nor a fungus, nor an animal – according to the latest research, it may represent a completely unknown evolutionary lineage that has since gone extinct.

The living world of the ancient Earth was far more alien and unpredictable than we might imagine based on today’s plant and animal life. At the dawn of life on land, not only did the first plants and simple animals appear, but also ancient organisms whose structure and functioning bore no resemblance to anything alive today. These so-called evolutionary dead ends have long since vanished, yet their fossils continue to raise new questions about the origins and diversity of life.

The discovery of Prototaxites

The story of one of the strangest fossil organisms began in 1843, when the remains of Prototaxites were first discovered, and it was immediately clear that something unusual had been found. The unbranched, cylindrical organism resembled a tree trunk more than any known living thing, and its sheer size was astonishing in itself: some specimens may have reached a height of 26 feet (around eight metres), while their width could exceed one metre.

Over the decades, the scientific community was unable to agree on what this ancient life form actually was. It was initially thought to be a plant, later an alga, and eventually, following a chemical analysis published in 2007, the dominant theory for many years held that Prototaxites was a gigantic, ancient species of fungus. This interpretation was based on the assumption that the organism fed on decaying organic matter rather than relying on photosynthesis.

An ancient life form on an extinct evolutionary branch

Recent research, however, has fundamentally overturned this view. According to a study published in Science Advances, the anatomical and chemical properties of Prototaxites do not fit those of either fungi or plants.

The research focused on a species called Prototaxites taiti, discovered in the Rhynie chert in Scotland – a site of exceptional importance due to its extraordinarily well-preserved fossils of early land plants and animals. Although this species was much smaller than its relatives, measuring only a few inches in height, it is nevertheless considered the largest Prototaxites specimen found in the region.

When examining the fossil’s internal structure, researchers identified a tubular construction that at first glance resembled the internal structure of fungi. The details, however, revealed crucial differences: the branching and reconnection of the tubes followed a pattern that has not been observed in any known group of fungi.

Impossible to classify within existing taxonomic categories

Chemical analyses revealed even clearer discrepancies, as Prototaxites fossils contained no chitin, a fundamental component of fungal cell walls. Instead, the studies pointed to the presence of lignin-like compounds, which are typically found in the bark of plants. This contradictory combination – a fungus-like structure paired with plant-like chemical characteristics – further strengthens the idea that Prototaxites represents a completely distinct ancient life form.

According to the researchers, all of this suggests that Prototaxites cannot be placed within any currently recognised taxonomic category. Although it may have belonged to the eukaryotes, it does not fit among fungi, plants, animals or protists. Instead, it may represent an evolutionary lineage that has since become entirely extinct and does not share a common multicellular ancestor with any living organism today.

Further research will be required to gain a more precise understanding of what this ancient life form was, how it functioned, and what ultimately led to its extinction. One thing is certain, however: its existence serves as a reminder that the story of evolution still holds many surprises for us.

If you happened to miss it, you can read about another discovery that also reshaped our understanding of evolutionary history in this article.