Morphogenesis of the Septum in Ammonoids

  • Antonio G. Checa
  • Juan M. Garcia-Ruiz
Part of the Topics in Geobiology book series (TGBI, volume 13)


Ammonoid septa are aragonitic structures that divide the shell internally into a series of chambers, the most adorai of which (also the largest one) is the living chamber and is occupied by the ammonoid’s soft body. The septal surface is roughly transverse to the shell tube. The most typical feature of the septum is its marginal corrugation. Individual folds are given different names according to their polarity. Adorally bulging major folds are called saddles, and apically directed folds are lobes. Minor elements of saddles and lobes are folioles and lobules, respectively. Marginal complication progressively decreases toward the septum center, which is a slightly undulated to flat surface. For each saddle or lobe, the fold or element placed opposite (i.e., linked by a minimal distance through the septum to the other side or to the other wall of the whorl cross section) is always of the same polarity (Figs. 9, 10). Therefore, the septum is adorally concave when sectioned across two opposite saddles and adorally convex when this is done across opposite lobes. On the basis of this property, the septum is an anticlastic surface.


Fractal Dimension Koch Curve Whorl Section Viscous Finger Septal Neck 
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Copyright information

© Springer Science+Business Media New York 1996

Authors and Affiliations

  • Antonio G. Checa
    • 1
  • Juan M. Garcia-Ruiz
    • 2
  1. 1.Departamento de Estratigrafía y Paleontología, and Instituto Andaluz de Ciencias de la TierraUniversidad de Granada, Facultad de CienciasGranadaSpain
  2. 2.Instituto Andaluz de Ciencias de la TierraConsejo Superior de Investigaciones CientíficasGranadaSpain

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