Palaeozoic wood rot mistaken for oribatid mite coprolites
deutsche Version

Conspicuous tiny clots related to local damage in the wood of fossil trees are usually interpreted as coprolites, also more specifically as mite coprolites or even oribatid mite coprolites. Recently, evidence contradicting such interpretation has been compiled: see Misconceptions, Oribatid mite coprolites. It is worth mentioning that most evidence is taken from published pictures whose authors did not notice essential details. As the proponents of the coprolite hypothesis are reluctant to accept contrary arguments, more evidence is extracted from their publications here. 

clot inside tracheid, no coproliteFig.1: Lower Permian wood from Schallodenbach, Germany.
Note the small clot deep inside a tracheid.  Detail of Fig.30 in [1].

clots in Permian wood cells, no coprolitesclots inside Permian wood cells, no coprolitesFig.2 (left): Lower Permian wood, Schallodenbach; more of it here.

Fig.3: Lower Permian wood, detail of Fig.4F in [2].
The clots are essentially globular when smaller than the cell cross-section.
The arrangement of the clots hints at a process of clot formation propagating from cell to cell.

Compared to the tube-like xylem cells, the clots appear globular. They may be really globular as long as they are smaller than the cell cross-section, as in Figs.1,2,3. Bigger clots either fit nicely into the angular cell lumen and keep their shape after the cell walls have gone, as in Figs.4,5, or they expand and deform the cell and remain essentially globular. It is not known under which conditions one or the other of these options, or some intermediate stage, is realized.

Psaronius aerial root phloem cells empty or filled with clot matter angular clots in Permian wood, no coprolitesFig.4 (left): Psaronius aerial root cross-section, phloem cells empty or completely filled with clot matter. Detail of Fig.8 in [3].

Fig.5: Lower Permian wood, angular clots released after disintegration of tissue.
Detail of Fig.3I in [2].

The observations suggest that the clots grew inside the cells, and are no mite droppings fallen into the open end of damaged tube-like cells and slid down as claimed by the supporters of the coprolite idea [4]. Sliding down a tube under its own weight is a notion which does not apply to things as tiny as cell-size clots because adhesion forces would
exceed their weight and make them stick to the wall, all the more so in the presence of traces of moisture. Obviously the clots seen inside the tubes in Figs.6,7,8 grew there on the very spot where they are now, judging from the bulges.

Permian wood tracheids with bulges due to clotsPermian wood tracheids with bulges due to clotsPermian wood tracheids with bulges due to clots
Figs.6,7,8: Permian wood with clots inside the tube-like tracheids causing them to bulge, which indicates that the clots grew there and hence are no coprolites. Details of Fig.4D in [2].

Permian wood, clots in filesFig.9: Lower Permian wood, clots interpreted as coprolites in [3] although they are arranged in rows, slightly tilted to the right but compatible with the files of empty cells below. Detail of Fig.17 in [3].

The rows of clots in Figs.2,3,9 suggest a formation process spreading along cell files. This is also suggested by pith rays filled with dark substance in Fig.10 and in [3], Fig.17, and by observations on [2], commented in [5]. clots in damaged Permian woodThe tissue in the upper half of Fig.9 is deformed but apparently still coherent. Hence, what is described as a frass gallery in
[3], Fig.17, is locally deformed wood affected by a process producing dark substance inside the cells. The narrow vertical line crossing some clots is a crack formed at an early stage of silicification.

Fig.10 (right): Lower Permian wood cross-section with alleged "mite borings and galleries containing coprolites", detail of Fig.6C in [2], interpreted here as wood rot involving the formation of dark substance in the cells and pith rays, with subsequent disintegration of the tissue.

As a conspicuous feature, the clot sizes vary strongly, and so do the cell sizes in this particular sample. Some clots may have grown bigger than the tracheid diameter, as in Figs.6,7,8.
A large part of the clots are angular, as distinctly seen above left. The angular clots preserve the shape and size of cell cross-sections after the cell walls have dissolved, as emphasized in [6].
A few clots are still inside cells in areas where the affected tissue is not yet disintegrated.
The process producing the dark substance has entered into and spread along part of the pith rays, delaying their disintegration. One affected pith ray is seen preserved where the surrounding tissue is not. More pith rays with dark fill are seen in [2], Fig.6C, and in [3], Fig.17. The dark area in Fig.3 is possibly also a filled pith ray.
To summarize, all clots seen in these pictures, except for Fig.2, have been mistaken for coprolites in the scientific literature. Fig.2 is taken from an own sample found and kindly provided by 
Ch. Krüger,  Schallodenbach. The arrangement of the clots in Fig.2 raised doubts concerning the coprolite interpretation. The doubts increased with every careful inspection of publications on the subject. A set of simple rules has been proposed in [7] as an aid for telling apart true and false coprolites.
The question remains what the clots are if not coprolites. A similarity to clusters of very thin hyphae of the fungus Glomites rhyniensis in cells of Lower Devonian plants is pointed out in [8]. However, Glomites is known to propagate through the intercellular space with coarse hyphae in addition to the thin ones inside cells but no coarse hyphae have been seen in the tissues with the clots considered here. So one has to consider formations by other fungi or by microbes as potential explanations for the clots.

H.-J. Weiss             2011

[1]  R. Noll, V. Wilde :  Conifers from the „Uplands“ – Petrified wood from Central Germany, 
      in: U. Dernbach, W.D. Tidwell : Secrets of Petrified Plants, D'ORO Publ., 2002. 88-103
[2] Zhuo Feng, Jun Wang, Lu-Yun Liu :
      First report of oribatid mite (arthropod) borings and coprolites in Permian woods from the Helan Mountains of northern China.
      Palaeogeography, Palaeoclimatology, Palaeoecology 288(2010), 54-61.
[3]  M. Barthel, M. Krings, R. Rößler: Die schwarzen Psaronien von Manebach, ihre Epiphyten, Parasiten und Pilze.
      Semana* 25(2010), 41-60.      * recently re-named, former name: Veröff. Naturhist. Mus. Schleusingen.
[4] Z. Feng, R. Kretzschmar: private communication.
[5] Dubious oribatid mite coprolites once more:  Comment on Z. Feng et al. (2010),           
[6] Alleged coprolites - Remnants of decayed tissue.           
[7] Alleged arthropod coprolites re-interpreted.         
[8] Alleged coprolites of "unknown creatures" replace alleged oribatid mite coprolites.
Annotation: A critical comment on [3] (in German) suitable for publication in the journal "Semana" has been rejected on grounds of pretended copyright violation.
quartz crystal with wood inside
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