Studied Material State of Preservation and Methods

We have been able to borrow three specimens (FMNH PE 32521, PE 20808, and PE 28955) of the six specimens assigned to Jeletzkya by Saunders and Richardson (1979). One of the specimens (?Jeletzkya douglassae Saunders and Richardson, 1979: Fig. 10, PE 28955) appears to have been assigned to the Cephalopoda erroneously. Specimen PE 32521 (Saunders and Richardson, 1979: Fig. 9 a, b, d) preserves the arm hooks and an unusual radula structure. In addition, this specimen shows remnants of muscular mantle and probable ink that were not observed previously. The specimen PE 20808 shows a well-preserved adoral projection. In both specimens the shell has a similar gross morphology and size. However, in neither fossil is the shell material preserved.

Specimen PE 32521 (Fig. 6.1A, B) shows its ventral side on split halves of a medium-sized, flat, brownish ironstone concretion. The shell is weakly compressed because of compaction. It has a triangular shape, with a pointed adapical end and almost straight sides. It consists of a proostracum-like structure, a body chamber, phragmocone, and an irregularly calcified rostrum. A radula is situated approximately in the middle of the length of the proostracum-like structure (Figs. 6.2-4). More than 20 arm hooks are preserved in front of the shell aperture, and most are more-or-less randomly dispersed (Figs. 6.5, 6), except in two cases where they occur in pairs. It is not possible to reconstruct the arm crown from the arm-hook distribution. Most of the hooks are exposed in cross, or longitudinal sections, but some show their sides and provide details of their gross morphology. The outer surface of the body chamber bears a dispersed black substance that SEM study suggests is probably ink (Fig. 6.7C, E). SEM analysis of the material bordering the body chamber and excavated from the middle of its length revealed numerous soft-tissue debris (Fig. 6.7A), some of which presumably belonged to the muscular mantle (Figs. 6.8-10). Specimen PE 20808 is also exposed on its ventral side and shows a nearly complete proostracum-like structure.

Initially, both specimens were examined under a dissecting microscope (x7 to x35 magnification) under alcohol. In specimen PE 32521, the structure of the rad-ula, arm hooks, presumed ink, and muscular-mantle tissues were examined with SEM. To prevent destruction while making the SEM preparation, the specimen was trimmed from the concretion as part of a slab about 10 mm thick. The length of the slab (about 80 mm) was much longer than typical SEM preparations (usually 1020 mm). To diminish charging that could occur under high voltage in the SEM, the opposite side of the slab was coated with colloidal silver.

The occurrence of fossilized ink in specimen PE 32521 was revealed by SEM examination of the black material on the surface of the specimen and by comparison with the previously studied ink and other kinds of organic substance in present-day and extinct cephalopods (Doguzhaeva et al., 2002b, c, 2003, 2004a, b, c; Doguzhaeva and Mutvei, 2003, 2005). The characteristic structure of the ink was compared with the structure of the sediment in the concretion around the specimen. In order to detect fossilized ink substance in specimen PE32521, pieces of dark material were sampled from the shell surface. In order to display presumed mantle remnants, tiny pieces (less than 5 mm in size) were removed from the groove between the shell and the sediment. For their SEM analyses, the selected fragments of the specimen were coated with gold. The same pieces also were used for EDAX analysis to determine the chemical composition and diagenesis of the presumed muscular mantle debris and ink during fossilization. For EDAX analysis seven spectra were taken, four from the remnants of soft tissue and ink and three from the sediment.

SEM and EDAX analyses were carried out with Hitachi S-4300 at the Swedish Museum of Natural History, Stockholm.

The studied material is reposited at the Field Museum of Natural History in Chicago, USA (FMNH PE 32521, PE 20808, and PE 28955).

Fig. 6.1A, B. Saundersites illinoisiensis g. and sp. n, PE 32521. General view (A - part and B - counterpart) shows the cephalic area (CHA), proostracum like structure (PRO), body chamber (BCEI), probable phragmocone (PH), and probable rostrum (RO), Upper Carboniferous, Middle Pennsylvanian, Desmoinesian (Westfalian D), Francis Creek Shale, Mazon Creek, northwestern Illinois, USA. Scale bar is 1 cm.

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