''Prototaxites'' is an

extinct Extinction is the termination of an organism by the death of its Endling, last member. A taxon may become Functional extinction, functionally extinct before the death of its last member if it loses the capacity to Reproduction, reproduce and ...

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

of large macroscopic

eukaryote The eukaryotes ( ) constitute the Domain (biology), domain of Eukaryota or Eukarya, organisms whose Cell (biology), cells have a membrane-bound cell nucleus, nucleus. All animals, plants, Fungus, fungi, seaweeds, and many unicellular organisms ...

dating from the

Late Silurian The Silurian ( ) is a geologic period and system spanning 23.5 million years from the end of the Ordovician Period, at million years ago ( Mya), to the beginning of the Devonian Period, Mya. The Silurian is the third and shortest period of t ...

until the Late

Devonian The Devonian ( ) is a period (geology), geologic period and system (stratigraphy), system of the Paleozoic era (geology), era during the Phanerozoic eon (geology), eon, spanning 60.3 million years from the end of the preceding Silurian per ...

periods. ''Prototaxites'' formed large trunk-like structures up to wide, reaching in length, made up of tiny interwoven tubules around in diameter, making it by far the largest land-dwelling organism of its time. The

taxonomy image:Hierarchical clustering diagram.png, 280px, Generalized scheme of taxonomy Taxonomy is a practice and science concerned with classification or categorization. Typically, there are two parts to it: the development of an underlying scheme o ...

of ''Prototaxites'' has long been the subject of debate. It is widely considered a

fungus A fungus (: fungi , , , or ; or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and mold (fungus), molds, as well as the more familiar mushrooms. These organisms are classified as one ...

, but the debate is ongoing. Its exact relationship with extant fungus lineages is uncertain. It was almost certainly a perennial organism that grew over multiple years. Several

ecologies Ecology () is the natural science of the relationships among living organisms and their Natural environment, environment. Ecology considers organisms at the individual, population, community (ecology), community, ecosystem, and biosphere lev ...

have been proposed, including that it was

saprotrophic Saprotrophic nutrition or lysotrophic nutrition is a process of chemoheterotrophic extracellular digestion involved in the processing of decayed (dead or waste) organic matter. It occurs in saprotrophs, and is most often associated with fungi ...

like many modern fungi, or that it was a lichenised

autotroph An autotroph is an organism that can convert Abiotic component, abiotic sources of energy into energy stored in organic compounds, which can be used by Heterotroph, other organisms. Autotrophs produce complex organic compounds (such as carbohy ...

Morphology

left, upDawson's 1888 reconstruction of a conifer-like ''Prototaxites'' Prototaxm10

With a diameter of up to , and a height reaching , ''Prototaxites'' fossils are remnants of by far the largest organism discovered from the period of its existence. Viewed from afar, the fossils take the form of tree trunks, spreading slightly near their base in a fashion that suggests a connection to unpreserved root-like structures. Infilled casts which may represent the spaces formerly occupied by "roots" of ''Prototaxites'' are common in early Devonian strata. Concentric growth rings, sometimes containing embedded plant material, suggest that the organism grew sporadically by the addition of external layers. It is probable that the preserved trunk-like structures represent the fruiting body, or

sporophore {{Short pages monitor

Ecological context

The

University of Chicago The University of Chicago (UChicago, Chicago, or UChi) is a Private university, private research university in Chicago, Illinois, United States. Its main campus is in the Hyde Park, Chicago, Hyde Park neighborhood on Chicago's South Side, Chic ...

research team has reconstructed ''Prototaxites'' as a branchless, columnar structure. It was the tallest living organism in its day by far; in comparison, the contemporary plant ''

Cooksonia ''Cooksonia'' is an extinct group of primitive land plants, treated as a genus, although probably not monophyletic. The earliest ''Cooksonia'' date from the middle of the Silurian (the Wenlock epoch); the group continued to be an important comp ...

'' only reached in height and itself towered over the "

moss Mosses are small, non-vascular plant, non-vascular flowerless plants in the taxonomic phylum, division Bryophyta (, ) ''sensu stricto''. Bryophyta (''sensu lato'', Wilhelm Philippe Schimper, Schimp. 1879) may also refer to the parent group bryo ...

forests" that grew beneath it, and

invertebrate Invertebrates are animals that neither develop nor retain a vertebral column (commonly known as a ''spine'' or ''backbone''), which evolved from the notochord. It is a paraphyletic grouping including all animals excluding the chordata, chordate s ...

s were the only other land-dwelling multi-cellular life. ''Prototaxites'' could have used its tall columnar structure for spore dispersal. Alternatively, if ''Prototaxites'' contained photosynthetic structures, the height would have increased its ability to capture light. The presence of

biomolecule A biomolecule or biological molecule is loosely defined as a molecule produced by a living organism and essential to one or more typically biological processes. Biomolecules include large macromolecules such as proteins, carbohydrates, lipids ...

s often associated with algae may suggest that ''Prototaxites'' was covered by

symbiotic Symbiosis (Ancient Greek : living with, companionship < : together; and ''bíōsis'': living) is any type of a close and long-term biolo ...

parasitic Parasitism is a close relationship between species, where one organism, the parasite, lives (at least some of the time) on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. The ent ...

algae, making it in essence a huge

lichen A lichen ( , ) is a hybrid colony (biology), colony of algae or cyanobacteria living symbiotically among hypha, filaments of multiple fungus species, along with yeasts and bacteria embedded in the cortex or "skin", in a mutualism (biology), m ...

, or even suggesting that it was an alga itself. However, the variability in the ratios in the

isotopic signature An isotopic signature (also isotopic fingerprint) is a ratio of non-radiogenic ' stable isotopes', stable radiogenic isotopes, or unstable radioactive isotopes of particular elements in an investigated material. The ratios of isotopes in a sample ...

δ¹³C between specimens of ''Prototaxites'' suggest that it was

heterotrophic A heterotroph (; ) is an organism that cannot produce its own food, instead taking nutrition from other sources of organic carbon, mainly plant or animal matter. In the food chain, heterotrophs are primary, secondary and tertiary consumers, but ...

. ''Prototaxites'' mycelia (strands) were

fossilised A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved i ...

as they invaded the tissue of

vascular plant Vascular plants (), also called tracheophytes (, ) or collectively tracheophyta (; ), are plants that have lignin, lignified tissues (the xylem) for conducting water and minerals throughout the plant. They also have a specialized non-lignified Ti ...

s. In turn, there is evidence of animals inhabiting ''Prototaxites'': Mazes of tubes have been found within some specimens, with the fungus re-growing into the voids, leading to speculation that the extinction of ''Prototaxites'' may have been caused by such activity. However, evidence of

arthropod Arthropods ( ) are invertebrates in the phylum Arthropoda. They possess an arthropod exoskeleton, exoskeleton with a cuticle made of chitin, often Mineralization (biology), mineralised with calcium carbonate, a body with differentiated (Metam ...

boreholes in ''Prototaxites'' has been found from the early and late Devonian, suggesting the organism survived the stress of boring for many millions of years. Intriguingly, boreholes appeared in ''Prototaxites'' long before plants developed a structurally equivalent woody stem, and it is possible that the borers transferred to plants when these evolved. ''Prototaxites'' became extinct in the Late Devonian as vascular plants rose to prominence.

Footnotes

References

External links

* * * * * {{Taxonbar, from=Q2061593 Late Devonian genus extinctions Devonian fungi Silurian fungi Pridoli first appearances Enigmatic fungus taxa Fossil taxa described in 1859 Paleozoic life of Ontario Paleozoic life of New Brunswick