Science Has Found a Whole New Kingdom of Life

Four hundred million years ago, the early Devonian Earth was an alien landscape dominated by mosses and lichens, with the largest plants being very small. However, towering cylindrical pillars known as Prototaxites stood 6 to 9 meters tall, dominating the landscape for 50 million years. These organisms' fossils have been found across continents and were a vital part of the early Devonian ecosystem, providing food and shelter for arthropods. Despite their tree-like appearance, they were long believed to be a form of giant fungi.

The classification of Prototaxites has puzzled paleontologists for centuries due to its blend of plant-like and fungi-like features. Early theories suggested they were two separate organisms (a rotting conifer and a fungus) or even a bizarre form of land-dwelling algae. In 2007, carbon isotope analysis ruled out plants, indicating Prototaxites were consumers like animals or fungi. This led to the prevailing theory that they were massive fungi, though their immense size presented a challenge given the limited biomass in the early Devonian.

Several issues challenged the fungal theory. Modern fungi thrive on organic material, which was scarce in the early Devonian. One hypothesis suggested Prototaxites were lichens (a symbiosis of fungus and algae), but no evidence of algae has ever been found. Another idea was that they were fruiting bodies supported by a massive underground mycelial network or foraging rhizomes. However, a new peer-reviewed study, initially published in 2025, has presented compelling evidence against the fungal classification.

Examining a well-preserved fossil of Prototaxites titi, scientists discovered structures atypical of fungi. Many Prototaxites species exhibit 'medullary spots,' which under magnification, reveal complex networks of interconnected, minuscule tubes, some 10 times smaller than the surrounding body. These networks, resembling blood capillary networks or alveoli, likely facilitated gas, nutrient, or water exchange and have no fungal analogues. Additionally, some tubes were banded and reinforced, similar to tracheid cells in plants, suggesting structural support for their height.

Complementing the structural findings, chemical analysis using infrared spectroscopy revealed the absence of chitin, a key component of fungal cell walls. By comparing Prototaxites specimens to nearby fungal and arthropod fossils from the Rhynie chert deposit, scientists demonstrated a distinct molecular makeup. This, combined with the earlier carbon isotope data ruling out plants, effectively eliminates both the plant and fungus kingdoms. Through a process of elimination, the authors conclude that Prototaxites represents an entirely new, extinct kingdom of life with no known close relatives to anything else on Earth.