Alleged borings in fossil wood and their possible formation
deutsche Version

Small areas of vanished tissue in coniferous fossil wood have repeatedly been explained with the wood-eating habit of oritabid mites [1] or unknown creatures [2], which has been refuted in
Fossil Wood News 4 and 5. Although it is easy to explain why the small cavities are not what they are usually thought to be, it is not obvious how they really could have been brought about. The presence of dark clots thought to be coprolites was offered as evidence supporting the interpretation as frass galleries. Thereby, contrary evidence was ignored: Often the alleged frass gallery is not wider than the alleged coprolite. Also the size and shape of the alleged coprolites often fit to the size and shape of the cells, and the clots may be found inside cells.Alleged frass gallery with coprolites in coniferous wood

Fig.1 (right): Alleged frass gallery with coprolites in Lower Permian coniferous wood, detail from Fig.17 in [2]. Obviously the alleged coprolites are cells filled with dark matter.
Alleged oribatid mite boring with coprolites
Fig.2 (left):  Alleged tunnel eaten by oribatid mites into coniferous wood, with angular clots interpreted as coprolites in [1], detail from Fig.3C in [1].

While Fig.1 may be explained by the presence of an infectious agent, a kind of wood rot, spreading successively from  cell to cell, Fig.2 seems to require a more complex explanation. The angular shape of the clots suggests that they, too, once had been confined to cells like those in Fig.1 and released when the cell walls decayed. What is unusual in Fig.2 is the circular section of the cavity, which is usually not observed in connection with cell-size angular clots. Hence it is interesting that there is a process of obscure nature which makes round holes into the wood, as seen in Fig.3. Peculiar type of hole formation in wood

Fig.3: Largely deformed wood by local expansion of unidentified cause. Note the continuity of the cell files where the bloated wood is connected to the compressed wood below. Width of the cavity 2mm.

Obviously the wood inside the cavity is bloated while the surrounding wood is compressed, with a wide
enigmatic gap which is not fully circular. Probably the deformation did not occur in the living tree but in the dead wood with the tissue still coherent but its strength reduced due to degradation.
The compression can be traced back to two components: the radial expansion of unknown cause and a superimposed shear deformation of the wider vicinity. The shear was of such orientation as to exert pressure from above right and below left, which manifests itself by the concentration of compressed tissue there and possibly also by the not quite circular section.
Also remarkable is the continuity of the cell files where the bloated tissue is connected to the compressed tissue below.
These observations are not sufficient to explain what had been going on here before silicification of the whole. One can only guess that it is another one of the various examples of fungus or microbial action.
Anyway, here is evidence that small holes in wood are not always borings. This supports the assumption that most of the alleged borings and frass galleries are no such, and that the cell-size clots seen there are no coprolites. Neither oribatid mites nor unknown creatures need be invoked to explain certain types of damage in Palaeozoic wood.

Sample of Fig.3: pebble found in 1994 in a dry creek in Utah (W 111°58', N 37°8' ),  possibly from Chinle formation.

H.-J. Weiss     2012

[1] 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.
[2] M. Barthel, M. Krings, R. Rößler: Die schwarzen Psaronien von Manebach, ihre Epiphyten, Parasiten und Pilze,
     Semana 25(2010), 41-60.
(For related references see Fossil Wood News 3-8.)
quartz crystal with wood inside
Fossil Wood News  14

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