450 million years ago, from the Ordovician period to the mid-late Devonian period 370 million years ago, giant fungi called "Prototaxites" grew on Earth. Initially attributed to plants, their remains were later found to be either fungi or giant lichens. They could reach up to a meter in diameter, with the largest ones growing up to eight meters high.
Comparisons with mushrooms found today would be superficial. Those mushrooms had no caps or other morphological features, just a big column. Why it was advantageous for mushrooms to reach such sizes can only be speculated. It would have been virtually impossible for a fungus to reach such a size, so they were probably lichens because a lichen has an advantage over a fungus in that part of the top of the organism is photosynthesized.
It should be noted that mushrooms or lichens could have reached this size at that time, not least because the land was not very populated in the Ordovician, Silurian, or first half of the Devonian. Animals did begin to inhabit the land in the Ordovician, but only a few groups of them, so mushrooms grew undisturbed. In the second half of the Devonian, big trees probably made it hard for them to live because they grew faster than the fungi and blocked the sun, and took away their food.
It is possible that the large trees, by shading them out or otherwise growing faster in size, may have contributed to the disappearance of the giant mushrooms, but it could be assumed that the small mushrooms grew and flourished, but none of them lasted as long.
Fungi, although a very important group of organisms are relatively little studied.
Nearly a million animal species have been named, and there are many different kinds of plants that people know about. However, only about 100,000 species of fungi have been named, and only about 500 of those are fossils. In nature, fungi decompose various organic substances and help plants with food, water, and signal transmission. They provide humans with beer, bread, and many other interesting and important things, but their biological history is unclear.
Normal-sized mushrooms, as we know them, are usually not preserved because they have no mineralized skeletons and nothing to preserve them, so finds are only possible in cases where some peculiar fossilization is taking place very rapidly. Such finds are known from about 55 million years BC onward and in even younger sediments.
Fossils more similar to the fungi that exist today appeared in the Carboniferous, about 350–300 million years ago, but their finds are mainly hyphae or subterranean parts of mycelium or organic matter, which are mainly fungi, or their spores. The remains are therefore microscopic, which does not attract the attention of researchers.
Similarly, mushroom remains can also be confused with plant remains. Fungal remains are usually found when studying other organisms, for example, parasitic fungi that leave their traces in animal bones and plants.