The ancient world was a weird and wild place filled with plants, animals, and fungi of all sizes and shapes. And it turns out, according to a recent study, that the prehistoric Earth may have been home to a fourth kind of organism which no longer exists.
The study, a preprint posted to BioarXiv, focuses on prototaxites, an extinct group of organisms which existed from the Late Silurian (between 443 and 420 million years ago) and the Late Devonian (between 420 and 386 million years ago). Despite having persisted for tens of millions of years, they went extinct long ago, seemingly replaced in the environment by large, thick-trunked trees.
While the extinction of a species is an ordinary part of evolutionary history, when the prototaxites died out, they may have taken an entire kingdom of life with them.
Prototaxites, strange giant organisms of the ancient world
Prototaxites were massive in stature with trunk-like structures up to 3 feet across and 26 feet tall. They were the first giant land organisms and they resembled a tree at first glance. Like a tree, they spread slightly at the base, suggesting a subterranean root structure. Their fossils exhibit concentric growth rings which suggest it grew through the addition of outer layers, year after year.
First discovered in 1843, these characteristics led early paleontologists to believe prototaxites were the fossilized remains of partially decomposed conifer trees. Even the name prototaxite means “first yew.” Still, its classification has been a source of contention for nearly 200 years. Over the decades, it has been considered a tree, a multicellular algae, and most recently, a giant fungus.
In 2001, a study published in the journal Review of Palaeobotany and Palynology, made the argument that prototaxites were fungal. Later studies looked at the mix of carbon isotopes in the fossils to figure out how they got their energy. Typical plants, which produce energy through photosynthesis, have a consistent carbon isotope signal from the atmosphere. Prototaxites, meanwhile, have a wider range of isotopes, suggesting they get their energy from a variety of soil mixtures, and supporting the fungi hypothesis.
Still, prototaxites have unusual characteristics which don’t match up with what’s expected from a fungus, leading a team of scientists to reconsider their classification. If the genetic gunslingers at InGen were building a prototaxite exhibit at Jurassic World, they might need to put them in their own separate wing.
Prototaxites might have been a fourth kind of life, distinct from plants, animals, and fungi
Scientists compared the anatomy and molecular composition of prototaxites with contemporary fungi and found them to be distinct from every known extant or extinct fungi.
In 2018, scientists studying a peripheral region of tissue from a fossilized prototaxite identified what they believed to be fertile structures made of tubes connecting to the inner tissues. This led to the classification of prototaxites as a “basal member” of an existing fungal group. However, those proposed fertile fragments lack any connection to the inner vegetative material.
In the new study, researchers suggested that if prototaxites are a fungus, then they should share molecular composition characteristics with living fungi. Molecular analysis revealed that the cell walls of prototaxites contain components similar to lignin, instead of the expected chitin or chitosan usually found in fungi.
“Having found no support for the most widely held view that prototaxites [were] fungal, we next reviewed possible placement in other higher taxonomic groups. No extant group was found to exhibit all the defining features of prototaxites,” study authors wrote. “Based on this investigation we are unable to assign prototaxites to any extant lineage, reinforcing its uniqueness. We conclude that the morphology and molecular fingerprint of P. taiti is clearly distinct from that of the fungi and other organisms preserved alongside it in the Rhynie chert, and we suggest that it is best considered a member of a previously undescribed, entirely extinct group of eukaryotes.”
Return to prehistory in Jurassic World Rebirth, in theaters everywhere July 2, 2025.