Another tangle of tubes in chert
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(revised version)
 Fossil tubes, a few Ám up to near 100Ám wide, with or without wall pattern, separate (Fig.1) or in tangles (Fig.2), are most often nematophytes. Their affiliation is disputed, hence they are listed in [1] under "Enigmatic Organisms". They are not often seen in the famous Rhynie chert. Judging from the few samples hitherto found, the tangles of tubes can be more or less aligned, or even strictly aligned as with Pachytheca Some of them seem to consist of smooth-walled tubes only, as those presented in Rhynie Chert News 13, 30, 40, 46, 92, 98, 99. Distinctly different is Nematoplexus with its evenly wound smooth tubes and occasional irregularly curved patterned ones among them [2]. A short fragment of such tube close to a "branch knot" of Nematoplexus in this sample is seen in Rhynie Chert News 151. A long tube of the same type is nearby: here Fig.1. It may be problematic to relate the forms to species. The separate tube in Fig.1 might belong to Nematoplexus,
 tube
Fig.1: Nematophyte tube fragment, diameter 26Ám, with
spirals or annular rings on the wall, spacing mostly 5-6Ám.
        (Part of the tube is hidden in the depth.) Width of the image 0.8mm.

This sample suggests an unexpected alternative interpretation: Before silicification, the big tubes with patterned wall in Fig.2 had probably been placed within a lump of organic gel, together with tiny filaments. As noticed by P. Strother [3], the fossil in Fig.2 strongly resembles Nematothallus pseudo-vasculosa known as compression fossils [4]. The size data are roughly compatible, including the dimly seen tiny filaments which seem to correspond with "tubes between 1.5 and 3Ám in diameter" seen on the lectotype of that organism [4,5].
Similar as with the tube fragments scattered sparsely throughout the chert, the tubes in the gel lump do not show branching nor other remarkable features, perhaps except for one peculiarity poorly seen above left: A big tube reduces its diameter to less than half, then ends.
What looks like a series of orderly turns of a screw in Fig.1 is often interrupted by disorder due to merging or branching turns, as also seen
repeatedly in Fig.2.

Fig.2 (below): Uncommon assemblage of nematophyte tubes as a separate patch, probably of silicified organic gel,
        with tube diameters centered around an average of 20Ám, and a wide variety of spacings between turns
        of the tube wall pattern. Width of the image 1.9mm, same scale as above.

tube patch
Drawing conclusions from only one sample may not be justified here but asking questions may be appropriate:

  -  Is there a phylogenetic connection between the wide tubes with annular /spiral wall pattern which are a main constituent of 
Nematothallus
     and the similar tubes which are only occasionally seen among the smooth-walled tubes of
Nematoplexus ?  
  -  Is the placement of this 3D-version of Nematothallus near Nematoplexus in the chert incidental?
   
Finally it may be mentioned that this sample of mere 0.28kg has offered several remarkable items:
Nematoplexus with tubes larger and smaller than hitherto known (2009, 2017), Nematoplexus with weakly curved tubes (2013), Castracollis eye (? 2015) and unidentified moults, an unknown archetypal charophyte (2016), and possibly the first 3D-version of Nematothallus as seen above (2017). Seems extremely wondrous !
Sample: Rh9/86 (2003, 0.28kg).
Annotation 2018: The tube wall patterns, more clearly seen in Rhynie Chert News 122, resemble the tracheid wall patterns of land plants. This has led to the following conclusion: "The study of the nematophytes will become more central to the issue of the rise of the earliest land plants because they clearly have developed a diverse and somewhat complex tubular anatomy, which in many ways appears to be analogous to vascular tissue [4]".

H.-J. Weiss    2017     (modified: June 2017)  2018    2020

[1]  T.N. Taylor, E.L.Taylor, M. Krings: Paleobotany, Elsevier 2009.
[2]  A.G. Lyon: On the fragmentary remains of an organism referable to the nematophytales, from the Rhynie chert, Nematoplexus rhyniensis.
      Trans. Roy. Soc. Edinburgh 65(1961-62), 79-87, 2 plates.        (Scale error on Plate I Fig.1: not x19 but x1.5)
[3]  P.K. Strother: private communication (2017).
[4]  P.K. Strother: Clarification of the genus Nematothallus Lang: J. Paleont. 67(1993), 1090-1094.
[5]  W.H. Lang: On the plant-remains from the Downtonian ... . Phil. Trans. Roy. Soc. London B 227(1937), 245-291.
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