Ancient Mushrooms: How Large Were They?

Before trees came to dominate the landscape, giant mushrooms ruled the Earth. These towering fungi, known as Prototaxites, were the tallest land organisms at the time, reaching heights of up to 24 feet (8 meters) with trunks up to 3 feet (1 meter) in diameter. The mystery of Prototaxites' true identity has long puzzled scientists, with hypotheses ranging from giant algae to lichens. However, in 2007, researchers from the University of Chicago and the Smithsonian National Museum of Natural History provided compelling evidence that Prototaxites was indeed a giant fungus, ending the 130-year enigma surrounding these prehistoric giants.

Prototaxites fossils: tubular anatomy, unbranched, non-septate tubes

Prototaxites fossils are characterised by their tubular anatomy, consisting primarily of unbranched, non-septate tubes. These tubes are arranged in concentric or eccentric rings, giving the fossils a tree trunk-like appearance. The fossil "trunks" can vary in size, with some specimens reaching up to 8.8 metres in length and 1.37 metres in diameter. Prototaxites fossils are believed to be the remains of the largest land organism during the Late Silurian and Devonian periods, towering over contemporary plants and other life forms.

The tubular structure of Prototaxites fossils has been a subject of intrigue and debate among scientists for many years. Early hypotheses suggested that Prototaxites could have been a type of tree, alga, lichen, or even a completely distinct organism. The absence of typical plant structures and inconsistent carbon isotope ratios led researchers to question its classification as a plant or alga.

Further studies provided evidence supporting the idea that Prototaxites was a giant fungus. Isotopic analyses revealed a highly variable range of carbon isotope ratios, indicating that Prototaxites was not reliant on photosynthesis and instead fed on a variety of substrates. This heterotrophic nature aligned with the characteristics of fungi. Additionally, the presence of biomolecules associated with algae suggested the possibility that Prototaxites might have been a massive lichen or had a symbiotic relationship with algae.

The tubular anatomy of Prototaxites fossils has been compared to the structure of modern liverworts, specifically the genus Marchantia. Researchers found similarities in the external structure, internal anatomy, and nutrition between Prototaxites and liverworts. The hypothesis suggests that Prototaxites fossils may be composed of partially degraded mats of mixotrophic liverworts, which include fungal and cyanobacterial associates.

The mystery surrounding Prototaxites fossils highlights the unique characteristics of this ancient organism. With no modern descendants or living relatives, Prototaxites stands apart from any known taxonomic group, representing a long-vanished branch of life that once thrived during the Late Silurian and Devonian periods.

20-foot-tall fungi: tallest organisms on land

The idea of 20-foot-tall fungi may seem like something out of a fantasy novel, but it was a reality during the Late Silurian to Late Devonian periods, approximately 420-370 million years ago. During this time, giant mushrooms, specifically those known as Prototaxites, towered over the Earth's landscape, reaching heights of up to 24 feet (8 meters) with trunks up to 3 feet (1 meter) in diameter. These towering fungi were the tallest land organisms at the time, far surpassing the height of contemporary plants like Cooksonia, which only reached 6 centimetres (2.4 inches) in height.

The mystery of Prototaxites' true identity puzzled scientists for over a century. The fossils resembled tree trunks, yet they predated the existence of trees. Initially, Prototaxites was thought to be a conifer, then a lichen, and various types of algae. However, in 2007, a breakthrough occurred when researchers from the University of Chicago and the Smithsonian National Museum of Natural History published a paper in the journal "Geology." They examined the levels of carbon isotopes in Prototaxites fossils and found that the carbon isotope ratios were inconsistent with those of plants or algae, indicating that Prototaxites did not rely on photosynthesis. Instead, it fed on a range of substrates, including the remains of other organisms. This, along with the discovery of fungal filaments within the fossils, led to the conclusion that Prototaxites was indeed a giant fungus.

The massive size of Prototaxites remains a subject of intrigue. Today, fungi typically remain close to the ground, so the question arises: why would a fungus need to grow to such towering proportions? One theory suggests that the height may have been advantageous for spore dispersal, allowing for wider dispersal ranges. Alternatively, if Prototaxites contained photosynthetic structures, its height could have increased its ability to capture light. Additionally, the presence of biomolecules associated with algae suggests the possibility that Prototaxites was covered by symbiotic or parasitic algae, which may have provided benefits to both organisms.

The extinction of Prototaxites is another intriguing aspect of its story. Evidence suggests that the activities of animals inhabiting Prototaxites, such as the creation of mazes of tubes and boreholes, may have contributed to its decline. However, it is also important to note that the rise of vascular plants during the Late Devonian period coincided with the extinction of Prototaxites, indicating a potential connection between the two events. Despite its eventual extinction, Prototaxites stands as a testament to the incredible diversity and size of prehistoric fungi, a time when giant mushrooms ruled the Earth before trees even existed.

Pre-dated trees: fossils resemble tree trunks

The existence of giant prehistoric mushrooms has long been a topic of debate among scientists. These mushrooms, called Prototaxites, were first collected in 1843. Canadian scientist J.W. Dawson studied Prototaxites fossils in 1857 and described them as partially rotten giant conifers containing the remains of decomposing fungi. However, this idea was disputed by rival scientist W. Carruthers in 1872, who insisted on the name Nematophycus ("stringy alga").

The taxonomy of Prototaxites has been a subject of ongoing debate, with proposals suggesting they were conifers, lichens, algae, or an ancient variant of a tree. The debate remained unresolved for over a century until 2007, when a team of researchers from the University of Chicago and the Smithsonian National Museum of Natural History published a paper in the journal Geology. They examined the levels of carbon isotopes in Prototaxites fossils and concluded that it was a giant fungus.

Prototaxites formed large trunk-like structures up to 1 metre (3 feet) wide and reached 8 metres (26 feet) in length. These structures were made up of tiny interwoven tubules around 50 micrometres in diameter. The fossils of Prototaxites resemble tree trunks, with a slight spread near their base. This unique structure led scientists to speculate that Prototaxites may have used its height for spore dispersal or to increase its ability to capture light.

The presence of biomolecules associated with algae suggests that Prototaxites may have been covered by symbiotic or parasitic algae, making it a huge lichen or even indicating that it was an alga itself. However, the variability in carbon isotope ratios between specimens suggests that it was heterotrophic, feeding on a range of substrates rather than relying on photosynthesis. This conclusion is supported by the fact that plants tend to have similar carbon isotope ratios, while animals reflect what they consume.

Giant mushrooms: ruled the Earth

Giant mushrooms, known as Prototaxites, ruled the Earth over 400 million years ago. These towering fungi were the tallest land organisms at the time, reaching heights of up to 24 feet (8 meters) with trunks up to 3 feet (1 meter) in diameter. The first Prototaxites fossil was described in 1859, and for over 130 years, paleontologists were baffled by this giant tree-like stump, unsure if it was a plant, an alga, a lichen, or something else entirely.

The mystery of Prototaxites' true identity remained unresolved until 2007, when researchers from the University of Chicago and the Smithsonian National Museum of Natural History published a groundbreaking paper in the journal Geology. By examining carbon isotope ratios in Prototaxites fossils, they discovered that it was indeed a fungus. Unlike plants, which obtain carbon from carbon dioxide in the air, animals' carbon isotope ratios reflect what they consume. The wide-ranging isotope ratios in Prototaxites specimens indicated that the organism fed on a variety of substrates, including the remains of other organisms.

Prototaxites fossils have a unique structure, composed of primarily unbranched, non-septate tubes arranged in concentric or eccentric rings. This structure gave Prototaxites its impressive height, which may have enhanced its ability to capture light. Additionally, the presence of biomolecules associated with algae suggests that Prototaxites may have been covered by symbiotic or parasitic algae, further contributing to its height. While the reason for its enormous size is not fully understood, it is clear that these giant fungi created one of the Earth's first complex terrestrial ecosystems, long before trees evolved.

The extinction of Prototaxites occurred in the Late Devonian period, over 350 million years ago, as vascular plants rose to prominence. Evidence of arthropod boreholes in Prototaxites fossils suggests that the organism survived the stress of boring for millions of years. The extinction of Prototaxites may also have been caused by animal inhabitation, as mazes of tubes have been found within some specimens, with the fungus re-growing into the voids left by animals. Despite its eventual extinction, Prototaxites remains a fascinating example of the giant mushrooms that once ruled the Earth.

Mystery solved: University of Chicago and Smithsonian National Museum

For over a century, a giant tree-like stump had mystified paleontologists. Was it a plant, an alga, a lichen, or something else? This question remained unanswered for 130 years, until a fossil discovered in Saudi Arabia provided the final word.

In 2007, researchers from the University of Chicago and the Smithsonian National Museum of Natural History published a groundbreaking paper in the journal Geology. They examined the levels of carbon isotopes in Prototaxites fossils, which had long been a source of intrigue for scientists. By analyzing these isotope ratios, the team was able to determine that Prototaxites was not a photosynthetic organism, as plants and algae are. Instead, it fed on a variety of substrates, including the remains of other organisms. This conclusion was supported by the detection of a highly variable range of carbon isotope ratios in multiple Prototaxites specimens.

The research team's findings confirmed that Prototaxites was, in fact, a giant fungus. This conclusion was met with skepticism and disbelief, as the idea of a giant fungus was considered radical and unconventional. However, the evidence was compelling, and the mystery of Prototaxites' true identity was finally solved.

Prototaxites is now recognized as a branchless, columnar structure that towered over other organisms in its ecosystem. It was the tallest living organism of its time, reaching heights of more than 20 feet. The height of Prototaxites may have served a purpose in spore dispersal or increased its ability to capture light if it contained photosynthetic structures. While the mystery of Prototaxites' identity has been solved, it continues to intrigue scientists, offering a glimpse into the fascinating world of prehistoric fungi and the diverse nature of fungi in general.

Frequently asked questions