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Finite-element analysis of simulated ammonoid septa (extinct Cephalopoda): septal and sutural complexities do not reduce strength

Published online by Cambridge University Press:  08 February 2016

Marwan A. Hassan
Affiliation:
Department of Mechanical Engineering, McMaster University, Hamilton, Ontario L8S 4M1, Canada
Gerd E. G. Westermann
Affiliation:
School of Geography and Geology, McMaster University, Hamilton, Ontario L8S 4M1, Canada
Roger A. Hewitt
Affiliation:
12 Fairfield Road, Eastwood, Leigh-on-Sea, Essex SS9 5SB, United Kingdom
Mohamed A. Dokainish
Affiliation:
Department of Mechanical Engineering, McMaster University, Hamilton, Ontario L8S 4M1, Canada

Abstract

Finite-element analysis of circular septum models indicates that (1) anticlastic fluting weakened the last septa of the same radius of curvature by a factor of about 2.5 relative to the tensile stresses in a sphere of nacre, (2) septa with ammonitic sutures were stronger than those with goniatitic sutures of the same thickness, and (3) septa with more “complex” ammonitic sutures were stronger at the edge between lobes and saddles than “simple” ones. These results contradict recent claims that ammonoid septa became weaker as sutural complexity increased from goniatitic through ammonitic, so that the most complex sutures were limited to the shallowest habitats. The smaller marginal flutes of complex septa were relatively strong, allowing them to be thinner than the central septum and still act as elastic wall supports. Many Mesozoic ammonoids with highly sinuous sutures occurred in deep epeiric and open-ocean habitats, whereas it is those with secondarily reduced, ceratitic sutures that were typically associated with restricted shallow basins.

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Articles
Copyright
Copyright © The Paleontological Society 

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Finite-element analysis of simulated ammonoid septa (extinct Cephalopoda): septal and sutural complexities do not reduce strength
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