Thread by @GromesRoland

Ready for a #palaeobotany (?)/#palaeoart-thread?
Let's have a deep dive into my little piece "Will the real #Prototaxites please get up?"

Okay, so what is Prototaxites? It is a huge fossil known from the late Silurian (possibly even the mid Ordovician) to late Devonian, so (1/n)

from roughly 430(460?) to 350 million years ago. And "huge" is up to almost 9 meters in hight (length?) and 1 meter in diameter - in a time where most early land plants were mats of mosses or at best a few centimeters high!
But even more enigmatic than its huge size is its (2/n)

nature and the journey to try to unravel this is what I tried to depict.
In 1843 W.E. Logan collected fossil plants along the shores of Gaspé Bay and found among other, small specimens what reminded him of remnants of wood from a small tree. (3/n)

When John William Dawson first described the fossil in 1859 he named it Prototaxites as the growth rings found in the stem and the size and overall shape reminded him of yew trees (Taxus). (4/n)

In 1888 he published a reconstruction of Prototaxites as a conifer tree (1) - although he had already documented microscopic slices of the "wood", finding them to resemble fungal mycelia instead of normal plant cells. Dawsons classification was harshly critizized by (5/n)

W. Carruthers claiming that the fossil (he renamed it in disregard for taxonomic rules as "Nematophycus") had to be a fungus, lichen or alga, but nobody would be bonkers enough to consider it as anything but an algae (2). Carruthers classified it as a green alga but also (6/n)

compared it to the large laminarian brown algae. Despite Dawsons protests and insistence that Prototaxites grew in a terrestrial habitat the algal interpretation grew prevalent.
For an overview on early Prototaxites research see Huebner, 2001: (7/n) sciencedirect.com/science/articl…

A more modern algal interpretation of Prototaxites stems from H-J. Schweitzer who reclassified the 1974 described Mosellophyton hefteri, interpreted as a halophyte then, as a species of Prototaxites and compared it to laminarians (), we'll come back (8/n)link.springer.com/article/10.100…

to Mosellophyton later.
Another interpretation of Prototaxites - and definitely an unusual one - was published in 2010 by Graham et al. (), interpreting the fossil as rolled up mats of liverwarts. (3) (9/n) bsapubs.onlinelibrary.wiley.com/doi/full/10.37…

They based their interpretation on carbon isotope data, fitting a photosynthetic lifestyle of Prototaxites and interpreted the filamentous cells as rhizoids, root-like single cells anchoring liverwarts to the ground. While their interpretation may not have found too many (10/n)

supporters, I consider it an interesting hypothesis to compare others to and a reminder that taphonomy (the process of generating fossils) can sometimes create strange things we need to be careful interpreting! (11/n)

This covers the left part of my drawing - the "plant" interpretations of Prototaxites but we have to mention the early plant Cooksonia (9) - a centimeter high "giant" among plants at its time drawn for comparison. Ready to cross the river? (12/n)

Already in 1919 Arthur Harry Church remarked that Carruthers had rejected a fungal interpretation for Prototaxites to easily but it took almost a century for researchers to pick up that idea in earnest again with Huebner arguing in 2001 for a classification as a (13/n)

Basidiomycete based on micoanatomy and what he interpreted as the organisms spores (others later argued that these may have been spores of fungi feeding on Prototaxites!). As most fossils appeared unbranched he interpreted them as huge fruiting bodies of a fungus(4), (14/n)

growing over many years, undisturbed by competing plants and unmolested by animals.
I decided to add two individuals in states of damage to highlight how the fossils known could have arisen from these fruiting bodies, where 4a is simply fallen and broken, while (15/n)

4b is wheathered and cracked, maybe from storms, ligthning or arthropod feeding, not only resulting in a fossil easily (mis?)interpreted as branched and wrinkly but also allowing for algae, plants and fungi growing into the cracks, creating a potentially confusing fossil! (16/n)

Further research strengthened the interpretation of Prototaxites as a fungus, like analysis of its carbon composition hinting at a (mostly?) saprophytic lifestyle () and description of spore producing tissue hinting at it being an (17/n)ncbi.nlm.nih.gov/pmc/articles/P…

Ascomycete (), although this has also been challenged and others have put it to the Glomeromycetes or suggested it to be part of an extinct group of fungi. (18/n)pubmed.ncbi.nlm.nih.gov/29254969/

A different fungal interpretation based on microanatomical comparisons came 2022 from Vajda et al. who interpreted Prototaxites as megarhizomorphs, root-like structures allowing a huge fungal mycelium to reach new habitats (5) - of course this is not necessarily in conflict(19/n)

with other fungal interpretations as rhizomorphs have been suggested before and if Prototaxites grew in large part as a huge diffuse mycelium it may have generated different "organs" from this mass, possibly not connected in a way that fossilizes frequently... (20/n)

In 2002 Selosse picked up Huebner's interpretation arguing that it was valuable but not fully convincing as it didn't really provide an explanation for the organism's huge size and that the suggestion, predation by arthropods may have led to it's (21/n) cambridge.org/core/journals/…

extinction wasn't too convincing - however, interpreting Prototaxites as a huge lichen "tree" that was later outcompeted by plants might solve both problems!
An in depth description of a fossil known as the “Schunnemunk tree”, a branched almost 9 meter high specimen, (22/n)

in 2014 by Retallack and Landing portraits Prototaxites quite convincingly as such an organism (6, with the Schunnemunk tree as a dead individual depicted as 6a, compare to 4b!) (23/n)

tandfonline.com/doi/abs/10.385…

In 2022 Retallack has argued that Prototaxites and relatives like Mosellophyton (interpreted as distinct from Prototaxites again, 7) may have formed the first canopies on earth before land plants took over! (24/n)

sciencedirect.com/science/articl…

Lastly I couldn't help but add a little speculative interpretation - it has at several times been suggested that other fossils might be leaf-like structures belonging to the Prototaxites "trees", so I drew a lichen tree with short lived leafs where the "branches" are (25/n)

actually not yet-unfolded and the "wrinkles" of the stem the scars of shed "leafs", somewhat inspired by this piece of stunning Palaeoart by @MichaelChiappo3 (26/n)

So what is the real Prototaxites? I don't know and maybe we will never know with certainty - but I find the journey of reaserach and interpretation as fascinating as the fossil itself and I wanted to draw a hommage to that! (27/27)

P.S.1: A great overview on Prototaxites with many pictures can be found here: steurh.home.xs4all.nl/engprot/eproto…

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