Another type of structure superficially resembles a combination of drag bands and pseudosutures. They are marked by pairs of faint narrow dark lines within the lobes of Ceratites (SMNS 65537 and 65533, Figs. 10.3-10.5). In most cases, these lines are preserved only in the last two to ten chambers. These pairs of lines run more or less parallel to each other and more or less parallel to the flanks of the lobes. They ->
Fig. 10.6 (continued) (C) Lateral view of the left side. x 0.3. (D) Detail of E showing the tension wrinkles. x 4. (E) Detail of C, displaying the pseudosutures, drag bands and tension wrinkles. x 0.5. (F) Detail of B, note the drag bands. x 1. (G) Detail of A, showing incompletely filled chamber with serrate winnowing pattern. For the formation of internal moulds ofceratites see Seilacher 11966, 1968, 1971). x 3.
form very shallow elevations on the internal moulds. Their color differs from that of the sediment filling of the internal mould. Consequently, it appeared interesting to perform an element analysis again.
For this purpose, BSEI (back scattered electron imagery) pictures were taken of one specimen (SMNS 65533, Fig. 10.3). These images clearly show differences in the chemical composition of the dark lines and the sediment. The subsequent EDAX analyses, however, showed that, in contrast to our expectations, phosphorous is not present. The differences in composition between the dark lines and the surrounding sediment consisted in the higher content of the elements silicon, aluminum, and potassium, in addition to the expected elements oxygen and calcium. This probably reflects the predominance of one or several, possibly authigenic clay minerals which are present in a higher concentration than in the marly limestone of the internal mould. It is assumed that this difference in composition originated from the presence of organic matter.
Finally, the question arises whether this structure was formed during forward movements of the soft body or whether it represents some other kind of soft-tissue attachment structure. Since it is combined with dark-colored preseptal fields and with the scars of the unpaired ventral muscle in two of our specimens, it comes to mind that these structures might rather represent some kind of soft-tissue attachment, especially because only one set of these lines is preserved between two septa. Because the septal myoadhesive band probably runs more or less straight
across the flank (see 4.3), this structure cannot represent a part of the septal myoadhesive band. Therefore, these lines may rather present a pseudosuture.
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