Application of buckling equations to the functional morphology of nautiloid and ammonoid phragmocones

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Abstract
Analysis of the buckling equations demonstrates the high risk of buckling failure in large compressed ammonites and in orthoconic nautiloids, with too widely spaced septal sutures. Buckling equations also illustrate the difficulty of forming ammonoid septal membranes like soap bubbles. They also explain the need for intracameral walls in the cuttlebones of Sepia and the absence of apparently advantageous convex‐out septal surfaces in large, shallow‐water nautiloids. Buckling becomes more likely in large shells, particularly those with compressed whorls, such as the ammonite Placenticeras.