A dark side of palaeobotany 
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Aglaophyton with Glomites
A dark side of palaeobotany has developed nearly unawares during the latter two or three decades. It is centered around cell-size black clots in damaged or intact plant tissue, notably in petrified wood. Contrary to common sense, the clots have been offered as coprolites of never-seen mites or unknown creatures. This inconsistency did not bother those in the small circle of insiders who mutually exchange and read their own publications.
The mesmerising face shown here should serve as a warning to those who still promote the idea of dark fills in cells being coprolites.

Fig.1: Early land plant Aglaophyton, seldom seen well-preserved cross-section
, width 4.4mm, with forking central strand.
cells with dark fills, arranged as a ring, contain the symbiotic fungus Glomites rhyniensis [1]. Note also the cracks being deflected at the surface, indicating the presence of a waxy cuticle typical of land plants.
fungus clots in Rhynie chert
Fig.2: Aglaophyton
with dark fills of cells as in Fig.1,
here radial lengthwise
Figs.1,2: Rhynie chert, Lower Devonian.
It is unbelievably absurd to assume that cell-size clots resembling those in Figs.1,2 are coprolites. Fungus hyphae are
known to be able to enter into cells and form a clot there by prolific branching, known as an arbuscule [2].
In order to demonstrate the absurdity of the widespread coprolite hypothesis, a few details have been taken from the  scientific literature.
The authors [3-7] and several others do not wonder how the alleged fecal clots got into cells, occasionally one beside another in a row (Figs.3,6,11,12).
Clots which fill the angular cell cross-section are shaped accordingly but
smaller ones can be nearly spherical. Apparently they are stiffer than the degraded tissue so that they retain their shape when the empty cells are squeezed (Fig.4).
clots in cells
Fig.3: Rows of globular black clots in Permian wood from China, not filling the cell cross-section but apparently being attached to the wall: alleged coprolites in [3], Fig.4F.
Fig.4: Longitudinal cut of Permian wood, slightly squeezed tracheids with stiff clots inside: alleged coprolites in [3], Fig.4D. 
(See also Fossil Wood News 5, 8.)

dark fill in phloemclots in woodclots in woodclots in woodclots in wood Figs.5-9: Clots in Permian wood from Thuringia, Germany:
Fig.5 (far left): Psaronius phloem cells completely filled with dark substance: alleged coprolites in [7];
Figs.6,7: alleged coprolites in [4] Abb15: row of clots (Fig.6), clot with pentagonal contour (Fig.7), similar cells and one big flat-sided clot nearby;
Figs.8,9: "Twin clots": alleged coprolites in [5], Fig.1C.

clots in woodfungus clotsrow of clots in decayed woodfungus clot in wood cell
Fig.10-13: Clots in Permian wood from Germany:
Fig.10: Wetterau, Hesse, alleged coprolites in [6];
Fig.11,12: Schallodenbach, Rhine-Palatinate, own sample.
Fig.13: Döhlen basin, Saxony, own sample.

The professionals fond of the elusive mites [3-7] would doubtless misinterpret the few own samples (Figs.11-13) which essentially do not differ from theirs in Figs.3-10. Fig.12 is exceptional since the clots are still in their original position although the cell walls have disappeared. In Fig.13, hyphae seem to have grown between the cells before one of them supposedly entered into a cell and branched profusely into a clot there, which eventually turned
dark. It is not known whether there is a connection to the hematite above.
it is nearly self-evident that clots inside plant cells cannot be coprolites, additional evidence from the Rhynie chert (Figs.1,2) may help to convince those who would not see the simple truth. 

Own samples:    Fig.1: Rh2/73.1, obtained from J. Shanks, Rhynie 2002,    Fig.2: Rh2/83.2    Fig13: Bu7/111.2
                         Figs.11,12: Sch/3.1, obtained from Ch. Krüger,  Schallodenbach, Rhine-Palatinate, Germany

H.-J. Weiss   2015

[1]  T.N. Taylor et al.: Fossil arbuscular mycorrhizae from the Early Devonian,
      Mycologia 87(1995), 560-73.
[2]  T.N. Taylor, E.L. Taylor, M. Krings : Paleobotany, Elsevier 2009, Fig.3.96.
[3]  Zhuo Feng, Jun Wang, Lu-Yun Liu :
      First report of oribatid mite (arthropod) borings and coprolites in Permian woods from ... China.
      Palaeogeography, Palaeoclimatology, Palaeoecology 288(2010), 54-61.
[4]  R. Rößler, R. Kretzschmar, Z. Feng, R. Noll:
      Fraßgalerien von Mikroarthropoden in Konifernhölzern des frühen Perms von Crock, Thüringen.
      Veröff. Mus. Naturkunde Chemnitz 37(2014), 55-66.
[5]  Zhuo Feng, J.W. Schneider, C.C. Labandeira, R. Kretzschmar, R. Rößler:  
      A specialized feeding habit of Early Permian oribatid mites.
      Palaeogeography, Palaeoclimatology, Palaeoecology 417(2015), 121-124.
[6]  K. Goth, V. Wilde :  Fraßspuren in permischen Hölzern aus der Wetterau,
      Senckenbergiana letaea 72(1992), 1-6.
[7]  M. Barthel, M. Krings, R. Rößler: Die schwarzen Psaronien von Manebach, ihre Epiphyten, Parasiten und Pilze.
      Semana 25(2010), 41-60.
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