Strange fossil assemblage in a chert sample

More or less well preserved land plants, algae, fungi, microbes,
creatures, and enigmatic organisms have been found in the fossiliferous chert from Rhynie. Every chert sample offers at least one of these items, and most often more of them are seen near each other. There are rare and not yet named species among the kinds of fossils listed above, perhaps with the exception of the land plants, whose 7 described species could well be the only ones in that Early Devonian habitat. Samples showing rare species combined give rise to wonder. One of such has provided the images discussed in Rhynie Chert News 29, 51, 101, and in this contribution.
Nematoplexus and other fossils
Fig.1: Assemblage of quite different fossils, including Nematoplexus, the "enigmatic organism" [1], confusing at first sight, on the cut face of a Rhynie chert sample of 0.28kg.
Width of the picture 4mm.


Shown here is a unique assemblage of fossils, two of them being highly interesting: a tiny screw-like Nematoplexus wrapped around a more "normal" one, a charophyte alga most probably of a species that had been overlooked hitherto, the crustacean Castracollis, and a moult part which cannot easily be assigned to it.
Most conspicuous is the slightly inclined section of the lengthy cylindrical body of Castracollis (or its moult), contrasting to its vicinity and to the
big rugged moult part of uncertain affiliation below.
Clearly seen below right is a fragment of a screw-like tube of Nematoplexus, screw diameter about 0.2mm, which is compatible with the majority of Nematoplexus screws in this sample.
The deformed screw-like tube with three turns seen above, with the upper halves of two turns cut off, reveals a surprise if magnified (Fig.2): A sleek screw-like tube, 0.07mm thread width, 6µm thick, is wound around one turn of the big tube of 17µm thickness.
tiny Nematoplexus screw
Fig.2: Two different screw-like Nematoplexus tubes, the big one deformed, two upper halves cut off, intertwined with a tiny screw with two turns seen, the upper one clearly, the lower one very faintly in the depth.
Width of the picture 0.4mm.

The sample contains more scattered fragments of the tiny screws. They are not only much smaller than the "normal ones" in this sample but also slightly smaller than the ones in the original publication [2], reported in [3]. The simultaneous presence of much differing sizes of screw-like tubes of the "enigmatic organisms" is an enigma in itself. It becomes even more enigmatic by including the various other types of tubes in this sample, doubtless all Nematoplexus.

A quite different kind of fossil in Fig.1 may have escaped the notice of the reader although it occupies a large area:  It is a charophyte alga with pale upward-curved branches apparently emerging from two or three whorls, hardly seen but probably positioned one above another with small distances in between, unlike other charophytes with usually larger distances between their whorls. Every branch consists of only few cells in a row, up to 0.13mm wide here. This dimly seen charophyte would not deserve attention if one could be sure it is Palaeonitella, the allegedly well-known charophyte alga in the Rhynie chert. This alga, however, hides a surprise which should startle botanists: As seen in pictures taken from the raw surface of this sample (Figs.3,4) not far from the cut plane of Fig.1, this alga is distinguished by a peculiar feature not known from any charophyte alga, fossil or extant: It is a flower-like arrangement of capsules on stalks, as discovered recently and first described in
Rhynie Chert News 73, 89, 90, 93.
alga "flower" with oogoniaalga "flower" with oogonia
Fig.3: Top view of an "alga flower" with capsules attached to a central column (not seen here) with slender stalks, surrounding branches poorly preserved. Picture size 1mm2.

Fig.4 (far right): Inclined view of an "alga flower" with capsules, empty or filled, surrounding branches mostly cut across, bluish.
Picture size 1mm2.

As more clearly seen in previous contributions, the capsules are surrounded by curved branches forming a protective basket. These baskets, arranged in a kind of umbel as seen in 
Rhynie Chert News 89, are more or less lopsided so that cuts may provide confusing arrangements of parts. In Fig.3, one branch cross section is rather large, 0.2mm. In Fig.4, one cell of the branch on the left, width 0.12mm, is seen in full length, 0.5mm. The number of capsules, counting also the dimly seen ones in the depth, seems to be 12 in Fig.3 and 6 in Fig.4. Capsules with black fill are not rare (see Rhynie Chert News 73) but the one with white fill seems to be unique.
Anyway, not the presence or absence of the various fills is the important problem here but the very presence of the capsules is. The capsules do not fit into the charophyte concept as we know it, with the well-known gyrogonites as female organs. A strong hint is given by the presence, in the same piece of chert, of globular organs not much different from the likewise well-known antheridia of the conventional charophytes (Figs.5,6).

new charophyte antheridiumnew charophyte antheridium
Figs.5,6: Globular organs found near the new charophyte, most probably antheridia, wrapped with narrow branches. Same scale as above, width 0.8mm.

The presence of antheridia strongly suggests an interpretation of the capsules in Figs.3,4 as oogonia. This would make the charophyte faintly seen in Fig.1, like similar specimens discovered recently, an achetype of all charophytes, dating back to ages when the gyrogonites had not yet been invented [4]. As an intriguing thought, many of the charophyte specimens taken for Palaeonitella might rather belong to the much different new species.  
Likewise undecided and inviting further research is the Nematoplexus problem with tubes spiralling, weakly curved, or straight, with smooth or stiffened walls, with the enigmatic "branch knots", with a variety of sizes (as in Figs.1,2), all together in this small chert sample. The fact that it is still uncertain to which branch of living beings the nematophytes belong may contribute to the fascination with the subject.

All pictures taken from Sample Nr. Rh9/86, found in 2003.

H.-J. Weiss     2017

[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 tables
[3]  www.abdn.ac.uk/rhynie/nemato.htm
[4]  H.-J. Weiss: First xanthophyte and new charophyte in the Rhynie chert.
      87. Annual Conference of the Paläontologische Gesellschaft, Dresden, 2016, 163.
106

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