The impossibility of inverted suture lines in ammonites



The biological organization of ammonites does not permit a true inversion of suture lines to occur. However, the complex pattern of the ammonite phragmocone - nacreous septa, membrane coverings, siphuncle, and soft body - does show ‘weak points’ in growth regulation. This provides several instabilities which lead to a pseudo-inversion caused by mechanical compression of the saddles.