Pseudosutures Drag Bands and Tension Wrinkles

Pseudosutures (or phantom sutures; Seilacher, 1988) can frequently be seen on the internal moulds of ceratites from the Germanic Basin, but also in other ammonoids (Zaborski, 1986; Hewitt et al., 1991; Weitschat and Bandel, 1991, 1992; Westermann, 1992; Landman et al., 1993; Checa, 1996; Checa and Garcia-Ruiz,

Fig. 10.4 Line drawing of the posterior part of the body chamber of Ceratites flexuosus Philippi, 1901, ventral view, SMNS 65533, col. A. Ehmann, atavus Zone, Upper Muschelkalk, late Illyrian, late Anisian, Middle Triassic, Neckarrems near Stuttgart, Germany (see Fig. 10. 3).

Fig. 10.5 Oblique view of Ceratites transgressor Wenger, 1957, SMNS 65537, 5-6m below the Spiriferina-bed, pulcher to robustus Zone, Upper Muschelkalk, late Illyrian, late Anisian, Middle Triassic, Wollmershausen near Crailsheim, Germany. Note the dark preseptal field and the paired dark lines in some of the lobes of the last chambers. x 1.

Fig. 10.5 Oblique view of Ceratites transgressor Wenger, 1957, SMNS 65537, 5-6m below the Spiriferina-bed, pulcher to robustus Zone, Upper Muschelkalk, late Illyrian, late Anisian, Middle Triassic, Wollmershausen near Crailsheim, Germany. Note the dark preseptal field and the paired dark lines in some of the lobes of the last chambers. x 1.

1996; Doguzhaeva and Mutvei, 1996; Tanabe et al., 1998; Richter, 2002). These are represented by fine lines running subparallel to sutures. Usually, a whole set of such lines is preserved between each pair of real sutures. Apparently, these structures were formed in the course of the translocation of the soft body by the insertion of organic pseudosepta before the insertion of a new septum. In some ammonoids, these lines do not only represent furrows in the steinkern surface but they additionally display a darker color than the surrounding sediment (Vogel, 1959; Hewitt et al., 1991; Richter, 2002).

In the ceratite specimen presented here (SMNS 18996-4), the pseudosutures are extraordinarily well developed (Fig. 10.6). Especially the saddles clearly display sets composed of several pseudosutures, whereas the lobes are associated with drag bands. The pseudosutures are more strongly developed and more closely spaced close to a real septum, possibly implying a faster rate of formation of pseudosutures and/or a deceleration and subsequent acceleration of soft body movement directly before and after the formation of a new septum. Each of the drag bands originates in one spike of the serration of a lobe.

The drag bands are strongest on the venter, ventrolaterally, and in the ventral half of the flanks of the last formed chambers. The fact that pseudosutures and drag bands are almost always combined with lobes and saddles in the same manner points at locally different processes involved in the translocation of the soft body and the formation of the sutural elements (for details see, e.g., Hewitt et al., 1991).

Additional to the pseudosutures and the drag bands, one saddle of the same specimen displays minute wrinkles (Fig. 10.6D). Approximately 10-12 such wrinkles were counted per millimeter. These wrinkles have an appearance similar to imprints of tension wrinkles (see Checa and Garcia-Ruiz, 1996: 290, Fig. 16). It is not completely clear because of the imperfect preservation whether these structures were truly situated on the septum or rather on the inside of the outer shell wall.

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