The year 1859 was a defining point for many biologists. Due to the publication of The Origin of Species by Charles Darwin, many now accepted evolution had occurred; where organisms alive today evolved by gradual change from earlier forms. This caused a massive wave of interest into the course of evolution. With animal evolution, study is relatively simple; a great mass of information is already known about morphology of the organisms, and, most important of all, features characteristic to animals, such as bone and teeth, are readily fossilised. However, with fungi, not only is the simple morphology a poor indicator of any past relationships, studies on fossilised fungi have been rare - one reason being the genuine lack of definitive fossil evidence. Still, this has not prevented many mycologists from phylogenetic speculation relating to the origins and subsequent evolution of fungi. The recent arrival of molecular methods of assessing relationships, with the comparative analyses of molecular sequences (nucleic acid and proteins), has, however, changed the situation massively. 

Fossil Fungi

The picture to the right represents a 400 million year old fossilized fungus (Paleomycetes) found in the renowned Rhynie Chert flora in Scotland (See links page). There are a number of reasons why many aspects relating to the evolution of fungi are difficult to establish from the fungus fossil record alone:

  • The vegetative states of fungi that are the same in the fossil record and in nature lack traits required for accurate taxonomic determination.

  • The most important aspects which have all the traits required for reliable taxonomic identification, the sexual states, are so tiny and short-lived it has been difficult finding them. It seems that such characteristics only appear in the fossil record millions of years after they have been around for a while.

  • In the fossil world, certain algae and protozoa make structures congruous to fungi.

  • Fungi can expand into rocks long after rock deposition, and modern fungal spores are always present in air and water, thus creating difficulties in distinguishing modern contaminants from genuine fossils.

However, it is only through fossil evidence that enigmas of ancestral fungi will be resolved. 

As new methods of data analysis elevate our curiosity in fungal evolution (such as molecular sequencing), we should not forget the evidence that the fungal fossil record can bring to the debate. Information from not only the mid-nineteenth century, when palaeomycology was first attempted, but also the present day provides substantial knowledge on the subject. The acquisition of new fossils, plus the re-examination of data regarding older specimens can only help the quest in discovering the secrets of fungi origin and evolution.

Click Here! For a time line summarizing the key events in fungal evolution.

The oldest know fossilized fungal spores have been found in amber dating back to 225 millions of years ago. Fossilized fungal spores in sediments of around 50 - 60 million years old can be found with relative ease. Such fossilized fungi are remarkably like those of extant groups, indicating fungi have had a long and stable existence. There is plausible evidence however that all present-day species of fungi existed long before the periods indicated by the fossilized fungal spore discoveries. 

Fungal Associations

Early terrestrial environments were harsh terrains, poor in nutrients and prone to desiccation. Mutually beneficial symbiosis of fungi and plants would have certainly assisted in the original encroachment of plants into such difficult terrestrial environments. Nearly all terrestrial plants in the modern day form such associations (estimates of around 80%), namely with arbuscular mycorrhizal (AM) fungi and it is postulated that these symbiotic relationships between AM fungi and the roots of higher plants were vital in the move of plants to a terrestrial environment. The plants generally benefit from enhanced uptake of water, minerals and nutrients. Conversely, the mycorrhizal fungi need their vascular plant host to survive, being obligate symbionts. The image here represents a mycorrhizal fungi, where the fungal mantle is surrounding the plants roots (See links page).

The earliest record of an AM fungus, in association with vascular plants, came from the 460 million year old Ordovician fungus of Wisconsin. The fossilized fungal hyphae and spores found strongly resembled modern AM fungi, in particular a member of the Glomales (which belongs to the phylum Zygomycota). Confirmation of such a finding came from experiments estimating divergence times based on ribosomal DNA sequences, in which they were consistent with the existence of a lineage of Glomales in the Ordovician period.

In addition to AM fungi, endophytes and lichens are two more illustrations of fungus-plant associations. With a small number of exclusions, terrestrial plants all have endophytic fungi in their above-ground structures (such as leaves) and these associations are still necessary to the majority of land plants. Awareness of the fungus-plant mutualisms is essential for the collection of knowledge on fungi. To find older fungal fossils and further enhance evolutionary studies, we must now look into the symbiotic associations that fungi make, and if necessary, extend this to a broader range of organisms.

It is obvious that there is still much to learn about the fungal fossil record. Although the fossil record may never offer insight into the very earliest fungi, it is continuing to develop and assist ideas into the evolution of the fungi. No more so, in fact, than in the unique relationship the fossil record now has with molecular sequencing. It is hypothesized that interpretation of some fossil fungi will benefit from at least a rough estimate, attained from molecular data, of the timing of major events in the evolution of fungi. A relative time scale is established for the evolution of the fungi using a phylogeny from DNA sequence data, the time scale than calibrated by using correlations between phylogenetic events and events in the fossil record of fungi or fungal symbionts. 

Click Here! For details into molecular sequencing.

Origin of Fungi - Summary

Initial evidence of a unique evolutionary history between animals and fungi first came about in the year 1993. Due to work involving analysis and comparison of small subunit ribosomal RNA sequences, it was postulated that the animal and fungal lineages shared a more recent common ancestor than either does with plant, alveolate, or stamenopile lineages. The hypothetical protist that represented the most common ancestor to the animals and fungi was said to be a unicellular flagellated protist, similar to modern day choanociliates. Evidence for the specific phylogenetic relationship between animals and fungi was quite a finding - at varying times, fungi have been considered to be plants, members of other protists groups, and only recently worthy of a kingdom level status. Surely animals and fungi could not possibly be sister groups?! Since 1993, numerous more experiments have been performed, all restating the results found in that year. 

Due to the effect of the variable rates of evolution between the major kingdoms (Animal, plant and fungi), it is still not determined the exact sequence of divergence of the kingdoms. However, estimates of times of key events can still be formulated. Once again, all from evidence inferred from molecular sequence data, it appears that eukaryotes and bacteria shared their last common ancestor around 2000 millions of years ago. Plants, animals and fungi then began to diverge from one another in the region of 1000 millions of years ago. The important event to note here is that plants diverged first, thus fungi and animals shared a common ancestor more recently than either did with plants. The divergence of animals from fungi has been estimated at 965 millions of years ago.

See timeline for more information