The Giant Fungi of Devonian Earth
Prototaxites would have made the environment even more alien some 400 million years ago
Imagine yourself walking across the land of our world some 400 million years ago. Things were far different then.
The two main supercontinents, Laurentia (the North American craton) and Gondwana (the southern hemisphere landmass including present-day South America, Africa, Australia, India, and Antarctica), were on their way into colliding and forming Pangaea.
There was more carbon dioxide in the atmosphere then, but oxygen levels were on the rise.
Plants at that time were all very small but were on their way to creating great forests that would follow in the millions of years to come. The plants themselves mostly didn’t have roots and leaves and likely spread vegetatively (instead of using spores or seeds). Early vascular plants were just beginning to take form. They were the early progenitors of later things like the lycophytes and ferns.
Landscapes were likely mostly rocky with maybe some microbial films in nutrient rich areas but very little soil. Invertebrates had only just recently in geological history made their entry onto land, with some things like ancient millipedes and ancestral spiders and other early arthropods creeping about.
The entire landscape would have looked utterly alien to us now. Especially given one other creature that we know to have existed at that point…
This period of time is known geologically as the Devonian period.
While walking around in this lower oxygen, rocky, slimy environment, maybe stepping over mats of vegetative plant material standing a few centimeters tall or avoiding some of the strange little mites and millipedes and such, there’s at least one thing that might have stood out. Standing around you might have been giant columnar organisms we now know as prototaxites.
I first encountered prototaxites while scrolling through social media many years ago. “Really?! I'd never heard of these Prototaxites before. Must dig deeper,” I wrote to myself as a note, with the intention of learning more about them. Now, I can’t help but wonder what that alien environment of the Devonian some 400 million years ago here on Earth might have been like.
Thinking of giant prototaxites towering over a terrestrial landscape with plants and animals just beginning on their path to the biodiversity we see today also arouses some ideas about what alien worlds might be like.
The Ancient Giants: What Were Prototaxites?
The prototaxites (which is pronounced like “pro-toh-tax-eye-tees”) are one of nature’s many enduring enigmas uncovered by scientific study.
For years, scientists debated what prototaxites actually were. While some early ideas proposed that these giant structures might have been a strange sort of primitive tree or even a lichen—a symbiotic partnership between fungi and algae—most research currently suggests the prototaxites were ancient fungi.
Flourishing during the Late Silurian to Devonian periods (roughly 420 to 370 million years ago), these enormous organisms may have dominated some landscapes (we really don’t know how extensive they were, but fossils have been found in distant enough places to suggest that the prototaxites covered a large region of the land).
Fossils reveal that prototaxites could have stood upright and towered several meters high—imagine a living structure as tall as a small tree, yet made of material that many believe was fungal in nature. This has been the prevailing view of them for some time, though the 2022 paper, Prototaxites reinterpreted as mega-rhizomorphs, facilitating nutrient transport in early terrestrial ecosystems, suggests that the prototaxites might have laid horizontally, like giant tubular fungal hyphae stretching out across the landscape.
Heck, maybe they did both.
Here’s a fantastic video from the BBC that goes a bit deeper on the prototaxites:
The Role of Fungi in Shaping Life on Earth
Fungi have been indispensable in shaping Earth’s ecosystems.
Beyond the curious case of the prototaxites, modern fungi are crucial decomposers that recycle dead organic matter, turning it back into nutrients that feed new life.
As E.O. Wilson famously noted:
The world depends on fungi, because they are major players in the cycling of materials and energy around the world.
This cycling not only supports decomposition and plant growth but also stabilizes ecosystems by ensuring that energy and matter are continuously reused.
In today’s world, many fungi form symbiotic relationships with plants—mycorrhizal associations that help trees absorb water and minerals more effectively. In forests, these underground networks can span vast distances, connecting different species in what some describe as a “wood wide web.”
Fungi have been used by humans for food and medicine, have aided in religious ceremonies and psychedelic experiences, and may be integrated into future building materials for Mars and other frontiers.
The prototaxites may have been one striking part of the history of the development of fungi.
Prototaxites: Aliens on Earth and Beyond
The study of prototaxites offers us a glimpse into the distant past here on Earth and potentially other worlds.
In an era before flowering plants and dense forests, the terrestrial landscape was a rather alien place relative to what we know.
Prototaxites likely played a critical role in early ecosystems, serving as one of the first dominant life forms to colonize the land.
Their massive size and unique structure may have provided habitat for other organisms and influenced the chemical cycles of the time. Whether they stood tall above the landscape or were laying across the ground (or perhaps both!), they would likely have been major players in the breakdown of rocky material, formation of soil, and transport of nutrients.
The idea that a giant fungus could once dominate Earth leads naturally to imaginative questions about life on other planets.
Might similar life forms emerge in alien environments?
Consider a planet with conditions that differ radically from our own—a world with lower light levels, perhaps, or an atmosphere with a different composition. In such a setting, traditional plant life might struggle to thrive, but organisms with a fungal-like biology—capable of breaking down and recycling scarce resources—could become the primary architects of their ecosystems.
Fungi have survived multiple mass extinction events and continue to thrive in environments that range from the deepest forests to the harshest deserts.
On alien worlds, similar strategies might evolve to overcome environmental challenges. The ability to decompose complex materials, form symbiotic relationships, and colonize extreme environments could be key features of life on planets far from our own solar system. Even more radical to consider is the range of other possibilities for fungi.
Perhaps there are alien worlds with great interconnected fungal networks, like the giant fungi of eastern Oregon. There are five massive individuals there of Armillaria ostoyae (the Humungous Fungus). One of them is considered by some to be the largest organism on Earth (and extends over 3.7 square miles just under the forest floor). Could there be alien environments with even more extensive networks of fungal-like growth? The could be underground or maybe towering tall, but connected over entire continents or entire planetary surfaces.
While slime molds are not fungi (that’s a common misconception given their name), they behave in ways that make them somewhat similar to fungi while also being different. Slime molds are protists that can be “plasmodial” and have one gigantic interconnected cell with thousands or millions of nuclei in it or they can be “cellular” and have a large collection of individual cells that at certain points aggregate together (but there is lots of variation in these types as well). Slime molds can move over time and have even been shown to have some form of chemical memory and the capability to anticipate change. For this, some researchers have been exploring the nature of intelligence related to slime molds.
What if there are alien worlds where something like a fungal mycelial network or a slime mold became ever more intelligent? What if it created a form of communication, developing language as its first technology? Could there be alien worlds where giant fungi like prototaxites have become sentient and created civilization? Or a civilization of slime molds or other fungi who have come to dominate a world covered in other fungal forms?
Studying organisms like the prototaxites gives us pause to remember that our world itself has been alien to us in the past. They also remind us of the great potential for biodiversity out there in the cosmos.