Uronectes in translucent chert
deutsche Version
When this tiny fishbone-like structure appeared beneath the polished face of a big Permian chert lump found in 1995 in the Doehlen Basin, it came as a surprise since these cherts had not offered any creatures before. Soon it became apparent that this fossil is part of the tail of the crustacean Uronectes. [1,2]

Fig.1: Fragments of two of the five tail fins of the Permian crustacean Uronectes.
        Image width 1.4mm.

The 3D-aspect of the tail fins in this image is made more evident by the thin white lines, which are light reflections marking the small depressions on the polished chert face where there had been no chert but organic substance of the fin. From the shape of the white-lined inclined section it can be concluded that the stiffness of the fin had been provided by a flat hollow tube of roughly rectangular cross-section.
The less well seen tail fin below in Fig.1 reveals other details: There is no fishbone-like aspect on one side of the fin but sturdy bristles instead, poorly visible, with larger spacing. The biggest bristle is at the end on the left. So it appears that the tail fins in Fig.1 differ from those pictured in [1,2].
U tube

Fig.2: Fragments of unidentified parts of the Permian crustacean Uronectes.
        Image width 1.4mm, tube width 0.2mm.

More fragments of tail fins and exuviae of Uronectes have been found in the same chert sample. Most conspicuous in Fig.2 is the tube where the shadow inside supports a 3D-aspect of an uncommon corrugation with folds arranged along the tube. (In engineering applications, the folds usually run around the tube for better flexibility.)
A bright yellow crack, vertical in Fig.2, differs clearly from the pale yellow exuvia fragments: When it came upon a fragment offering an easy path for crack propagation, it followed that path until it resumed its vertical direction.
A few more chert samples with Uronectes have been found since but not yet evaluated.

Sample: B/52, found in 1995 at Bannewitz, Doehlen Basin, Saxony.

H.-J. Weiss 2022

[1] D. Uhl: Uronectes ... aus dem Rotliegend ... des Saar-Nahe-Beckens. Mitt. POLLICHIA 89 (2002), 43-56.
[2] H. Poschmann, D. Uhl:  Syncaride Krebse im Häutungshemd ..., Mitt. POLLICHIA Nr.10 (2007), 164-168,
in: "Kohlesümpfe, Seen und Halbwüsten, Dokumente einer rund 300 Millionen Jahre alten Lebewelt zwischen Saarbrücken und Mainz", Kapitel: Syncaride Krebse ..., Eds.: T. Schindler, U.H.J. Heidtke.

Scolecopteris pinnule cross-section, Sardinia Permian Chert News 42
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