Croftalania aspects
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The cyanophyte Croftalania [1] is found in the Rhynie chert as filaments and bulky tufts thereof, grown on substrates like silica gel surfaces or decaying plants in the swamp water. They are formed in a surprising variety of ways so that some of the shapes may resemble vegetables or styled hair. Several examples have been presented here:
Rhynie Chert News
56, 72, 125. The present contribution is meant to offer more of them.    
Inconspicuous separate filaments in
Rhynie Chert News 80, 144 are probably Croftalania but attention is drawn here to the conspicuous agglomerated masses of filaments.
Croftalania tufts growing on an alga tubeCroftalania tuft of filaments, shapedWhat looks like a 
monstrous face with excessive hair growth in Fig.1 is three bulky tufts of filaments growing outward from their site of attachment at the outside of a tube, probably of a charophyte alga. More often the tufts look as if trimmed by means unknown into wondrous shapes with distinct boundaries as in Figs.2,3.
Croftalania upon early land plant
Fig.1 (far left): Filamentous cyanophyte Croftalania grown in dense tufts on the surface of a cylindrical alga part. Image width 1mm.

Fig.2 (left): Croftalania tuft of filaments grown on a decaying plant part, trimmed into an "unnatural" shape. Image width 0.7mm.

Fig.3 (right): Fancy composition: Croftalania grown on a shrivelled early land plant, probably Nothia, lying in swamp water. Image width 5mm.

Apparently the early land plant cross-section with a thin black coating along the epidermis seen clearly in Fig.3, upset in the swamp water, had become coated with silica gel, which served as a substrate for Croftalania growing from there mostly upward towards the light. (The upward direction is indicated by level fills in former cavities in the same chert sample.)
By comparison with the diffuse boundary in Fig.1, the rather smooth periphery in Fig.3, including pointed tips, requires an explanation. Feeding crustaceans nibbling off the tuft ends smoothly had been proposed as a thinkable explanation of the clear-cut boundaries but doubts have remained. So it appears again 
that fossiliferous cherts do not only provide news but pose new problems as well.
Samples: Fig.1: Rh15/82 (0.19kg), Part 2, obtained from Barron in 2014.
              Figs.2, 3: Rh2/19 (8.3kg), Part 4: slab 12-14mm, found in 2001.

H.-J. Weiss   2023

[1]  M. Krings, H. Kerp, H. Hass, T.N. Taylor, N. Dotzler:
      A filamentous cyanobacterium showing structured colonial growth from the Early Devonian Rhynie chert.
      Rev. Palaeobot. Palyn. 146(2007), 265-276.
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