Ammonoid Septa and Sutures

Describing Ammonoid Conchs

“…The convention is that the saddles (Klug and Hoffmann 2015) point with their convex sides towards the top (aperture). The plane of symmetry (the center of the Elobe) is marked by an arrow, the umbilical shoulder (if present) can be indicated by a dotted line, the umbilical seam by a curve segment and the dorsal intersection with the plane of symmetry is indicated by either two straight dashes or two straight lines.…”

Cameral Membranes, Pseudosutures, and Other Soft Tissue Imprints in Ammonoid Shells

“…Some suggest that the temporary points of attachment served as critical, possibly genetically determined points that helped to maintain the shape of the rear mantle (and thus the consistent shape of the septum) between septa (Henderson et al 2002;Polizzotto and Landman 2010). This line of reasoning gives rise to the hypothesis that the pseudosutures represent points of temporary attachment for the rear body during translocation (Klug and Hoffmann 2015). In any animal possessing a chambered shell, growth requires repeated de-tachment of the body from the shell, yet it is unlikely that the animal would have detached the entire body simultaneously.…”

“…Some have interpreted drag lines as candidates for these tie points (Zaborski 1986;Seilacher 1988); others, however, point out that the coincidence of drag lines with the flanks of the lobules rather than the tips, and their paired occurrence, suggests that drag lines are more likely fused, telescoped pseudosutures (Hewitt et al 1991;Checa and Garcia-Ruiz 1996;Klug et al 2007;Klug and Hoffmann 2015). Polizzotto and Landman (2010) reported several different drag lines in a single chamber, none of which were continuous with the pseudosutures in the same chamber.…”

“…While Klug et al (2008) did not elaborate specifically on the consequences of this model for the formation of pseudosutures, the model implies that the shape of temporary attachment points would have depended on components of translocation that were not so much genetically influenced, but mainly affected by changes in chamber pressurization. For more details on septum formation see Klug and Hoffmann (2015).…”

“…According to Checa and Garcia-Ruiz (1996), these wrinkles document the flexibility of the organic membrane prior to the mineralization of the septum. For an illustration, see Klug and Hoffmann (2015).…”