Elusive creatures in fossil wood –
Clean-up in the wake of a waning obsession
deutsche Version
Since about two decades ago, reports on sightings of oribatid mite coprolites in Carboniferous, Permian, and Triassic wood appeared and became increasingly popular with time in some part of the palaeobotany community although the mites themselves remained unseen. Publications by R. Rößler, including a monograph [1], are a veritable repository of alleged mite coprolites, as pointed out before (Fossil Wood News 12). Neither the absence of mites nor the peculiar facts that the sizes of the alleged coprolites always agreed with those of the cells of nearby tissue, and that often the shapes were angular like the cells [2], gave rise to suspicion. Local damage to the tissue was interpreted as frass galleries even if the cavities were so narrow that no mite producing the cell-size clots could have crept there. clots in Permian woodNobody wondered about how the clots called coprolites could have got into intact cells, where they are seen more often than not. (Fossil Wood News 3, 5)  
The mite coprolite hypothesis has never been doubted in the scientific literature, and it proliferated by uncritical adoption. Own efforts with the aim to spread critical arguments had the effect that some authors do not speak about mite coprolites any more. Not so
R. Rößler [3,5] and Z. Feng [4,5], who seemed to have had a common interest in keeping up the coprolite fancy and evading any discussion on the subject. This resulted in the contributions Fossil Wood News 4, 5 and a writ by Rößler's lawyer declaring the mite coprolite hypothesis the state of science. While others have quietly dropped the idea, Rößler and Feng seem to be resolved to stick to it but they made the concession to abandon the "oribatid mites" and replace them by "unknown creatures" [3] or "new detritivores" [5]*. These are terms thought up in vain since the clots cannot be coprolites, which meanwhile has been demonstrated with numerous examples (Fossil Wood News 7).
What is left over from the subsided oribatid mite coprolite craze is its debris in the palaeobotany literature. The professionals who spread it are not inclined to clean up. The much praised ability of science to correct itself has got lost in parts of palaeobotany. Hence, weeding out the errors and misconceptions must be done by outsiders. A few more examples are presented here.
alleged coprolites in a tunnel in Permian wood
Fig. 1: Detail from [1], Bild 441, described there as a tunnel eaten into coniferous wood, filled with coprolites.
disarranged cells in Permian wood mistaken for coprolites

Fig.2 (right): Coniferous-type wood cells squeezed into an imperfect honeycomb structure by bloating apparently due to some expanding matter inside.
Detail from [4], Fig.6E, interpreted as oribatid mite coprolites there.

Doubts concerning coprolites in Fig.1 are raised by the observation that the clots are densely packed and of various sizes and shapes, on the average slightly bigger than the wood cells on the right and slightly smaller than the pith cells on the left. Comparison with similar structures (Fig.2) suggests that they are bloated and slightly displaced wood cells, filled with some light-coloured matter, as explained in Fossil Wood News 5. cavity in wood with bloated tissue insideSimilar phenomena are pictured in [6] and 
Fossil Wood News 21, Fig.7 there.

Fig.3 (right): Expanded tissue inside a cavity in silicified wood (Fossil Wood News 14). Width of the cavity 2mm.

There are more examples of cavity formation in wood in combination with the bloating of cells (Fig.3).

All that can be said here about the wood damage in Figs.1-3 is that there is some obscure connection with expanding cells but no connection with tunnel-boring creatures. The obsession of some authors with alleged arthropod traces in fossil wood had apparently misled them to the assumption that the furrows in the Lower Permian fossil wood in Fig.4 are burrows. As seen already on the image, the furrows have V-shaped cross-sections, often with a thin line along the bottom. Such furrows cannot be burrows.
cracks in Permian wood mistaken for burrows
Fig.4: Alleged arthropod burrows on the surface of Permian wood, after Rößler, detail of Bild 442 in [1], there with wrong scale. Width of Fig.4 as measured on the sample: 14cm. The furrows must be shrinkage cracks formed during silicification, later widened by spalling fracture on the crack edges: no burrows.misinterpreted cracks

                   Label to the sample of Fig.4
, Paläontologisches Museum Nierstein

According to the scale 4:1 in [1] the size of Fig.4 would be 1cm, which is highly questionable. A check at the Paläontologisches Museum Nierstein gave 14cm. Close inspection of the sample confirmed the conclusions already derived from the image: The wide furrows developed from narrow shrinkage cracks. Repeated impact of river pebbles caused spalling fracture at the crack edges, which created cross-sections with V-shape in the depth and rounded edges above. The original narrow crack, which may be filled owing to later silicification, is seen within some furrows as a thin dark line along the bottom, eventually with a tiny ridge left over from the broken away narrow crack fill. Needless to say that a boring creature could never make grooves of such peculiar shape.
Shrinkage crack formation during silicification is a common phenomenon. There are conspicuous examples in Permian wood from the Döhlen Basin.
burrows on the surface of Permian wood from Chemnitz
Fig.4 has been turned here such that the light comes from above left which makes a better 3D-impression. By the way, Bild 442 in [4] is the mirror image of the object, and so is Fig.4. This information may be useful for comparison with the sample.

Fig.5 (right): Galleries with U-shaped cross-sections without crack along the bottom, and cracks on the surface of a fossil tree trunk from Chemnitz. Detail of Fig.5 in [7]. Width of the picture 7.5cm.

Burrows and galleries below the bark would be U-shaped and without a narrow crack along the bottom, like those shown in Fig.5 for comparison.
juvenile mites in plant tissue
As a big surprise after so much vain talk about mite coprolites without mites we may have fossil mites without coprolites now. Gert Müller seems to have got the elusive mites in their burrows in plant tissue preserved in chert (Fig.6) [8]. As expected, none of the popular "coprolites" are seen there.

Fig.6: Juvenile arthropods in burrows in degraded tree fern tissue in Lower Permian chert, Freital, Döhlen basin, Saxony.
Width of the picture about 3mm. Sample and photograph by
Gert Müller. 

Amendment 2015:
After having avoided the disputed term "oribatid mite coprolites" for some time, R. Rößler has made use of it again recently [9,10] despite of plain evidence proving it ill-conceived: see Fossil Wood News 23, 24

H.-J. Weiss     2012,   updated 2013, 2014, 2015.

[1]  R. Rößler: Der versteinerte Wald von Chemnitz. Museum f. Naturkunde Chemnitz 2001
[2] H.-J. Weiss: Milbenfraß und Milbenkot, 6th Chert Workshop, Naturkunde Museum Chemnitz, 2007.
[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] Zhuo Feng, Jun Wang, Lu-Yun Liu: First report of oribatid mite (arthropod) borings and coprolites in Permian woods from ... northern China.
      Palaeogeography, Palaeoclimatology, Palaeoecology 288(2010), 54-61.
[5] Zhuo Feng, Jun Wang, Lu-Yun Liu, Ronny Rößler: A novel coniferous tree trunk with septate pith ...
      Int. J. Plant Sci. 173(2012),  835-48.

[6] H.-J. Weiss: Beobachtungen an Kieselhölzern des Kyffhäuser-Gebirges.
      Veröff. Mus. Naturkunde Chemnitz 21(1998), 37-48.
[7] R. Rößler, G. Fiedler: Fraßspuren an permischen Gymnospermen-Kieselhölzern ...
     Veröff. Mus. Naturkunde Chemnitz 19(1996), 27-34.
[8] G. Müller: private communication.

[9]  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.

[10]  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. 

quartz crystal with wood inside
Fossil Wood News 16

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