Well-known creatures and enigmatic formations in one piece of chert
deutsche Version
Fossil remains of early land plants, microbes, and fungi are abundantly preserved in the Rhynie chert. Much less abundant but not really rare are little creatures and their moults. Really rare are samples with more than one species of creatures inside, like the sample presented here.  
Most easily recognized are the cross-sections of trigonotarbids and their exuviae shed in moulting, often with hairy legs nearby. The slight inclination of the exuviae with respect to the cut plane in Fig.1 can give the impression of a thick wall but this is a mere illusion since the wall is very thin. Legs are clearly seen as cross-sections on the left. Legs are essential body parts for those spider-like predators with solitary ways of life on dry land.

Quite different is the aspect of the outwardly legless freshwater crustacean Ebullitiocaris (Fig.2): This egg-shaped, apparently mainly sessile creature feeding on algae is usually seen with several specimens near each other, and occasionally even in large numbers closely spaced and clinging to inundated terrestrial plants.
Fig.1 (far left): Trigonotarbid (Palaeocharinus) exuviae of body and two legs shed in moulting, thin-walled, slightly tilted cross-sections, with bluish chalcedony deposited inside along the wall.

, egg-shaped enclosure with an opening above as the only distinctly seen detail of the body.  Height of Figs.1,2: 1mm.

This chert sample seems to be the only one offering both Palaeo- charinus and Ebullitiocaris. In addition to the creatures easily recog- nized as such, it offers three phenomena with had been described repeatedly but not fully explained. Probably they are seen here for the first time combined in one plant cross-section: Fig.3.

Aglaophyton with scab
Fig.3 (right): Cross-section of Aglaophyton thrice affected, (image width 8mm):
(1)  enigmatic "flower-shaped" void pattern in the tissue,  
(2)  tissue decayed except for a peripheral layer of cells: "hollow straw aspect",  
(3)  large scab due to misguided growth.

   ad (1): Judging from other specimens (see Rhynie Chert News 4), the cavities seen radially arranged on cross-sections are extending along the shoot, thereby even passing forking sites Their occasional occurrence on some of the Aglaophyton specimens remains enigmatic. Most probably, the cavities in the upright living plant had been empty.
   ad (2): After formation of the void pattern most of the tissue in between decayed  except for surprisingly well preserved cells along the circumference which probably had been able to keep the shoot alive.
   ad (3): At some early stage the plant had developed a growth anomaly causing the tissue to grow a large scab,
locally interfering with the void pattern and "hollow straw" formation.  

The phenomena described so far could well have been there in the upright living plant while trigonotarbids prowled around. Eventually the vegetation became inundated in flooding. Microbes and algae thrived, providing food for the crustaceans dwelling between the plant remains. All cavities filled with water, included those which are empty now. For reasons unknown, chalcedony deposited itself differentially in the water-filled cavities inside the cross-section in Fig.3. While the cavities below did not get
filled with chalcedony, some aquatic fungus hyphae got the opportunity to grow there in the water. Later they became coated with tiny quartz crystals. After the supply of silica by diffusion had stopped, the cavities remained empty as they are now, crossed by coated hyphae.
The cuticle on the surface of the plant reveals its presence by deflecting the crack approaching from below left in Fig.3 such that it follows the plant surface until it runs into a crushed area.
Also worth mentioning here is a fact already discussed in Rhynie Chert News 105: The wall thickness of the "hollow straw" does not represent the silica diffusion depth as claimed in [1] but is brought about by the ability of the living plant to protect a fraction of the tissue against decay. Surprising evidence is provided by a very seldom seen phenomenon, shown in Rhynie Chert News 60, there Fig.4: At an early stage, local damage at the periphery had been covered with a cap whose cells, like those along the periphery, had been made decay-resistant in the live plant by unknown means. Hence, the wall thickness of the hollow straw, like that of the cap, had been brought about by processes in the live plant.
As noticed as early as 2010 and mentioned anew in 2014 [2], Ebullitiocaris is erroneously called rotifer in "Paleobotany" [3]. (See Errors and Mistakes. This erroneous interpretation has been included into fossilhunters.xyz ebullitiocaris: ... Peel Technique, Figure 157.)
Sample: Rh2/176.2, obtained from 
Shanks in 2012.   

H.-J. Weiss     2021

[1]  www.abdn.ac.uk/rhynie

[2]  H.-J. Weiss:  Rhynie chert – Implications of new finds.  EPPC 2014, Padua.
[3]  T.N. Taylor, E.L. Taylor, M. Krings: Paleobotany. Elsevier 2009.
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