Complexity of septal surfaces and suture lines in ammonoids – implications for the hydrostatic apparatus and palaeoecology using modern CT techniques Dissertation zur Erlangung des akademischen Grades eines Doktors der Naturwissenschaften an der Fakultät für Geowissenschaften der Ruhr-Universität Bochum vorgelegt von Robert Lemanis geboren am 22.06.1989 in New York (Vereinigte Staaten) i Erklärung „Ich erkläre hiermit an Eides statt, dass ich die vorliegende Arbeit selbständig angefertigt sowie die benutzten Quellen und Hilfsmittel vollständig angegeben habe. Ich habe alle Fakten, Textstellen und Abbildungen, die anderen Weken dem Wortlaut oder dem Sinn nach entnommen sind, durch entsprechende Zitate gekennzeichnet. Die vorliegende Dissertation wurde in dieser oder ähnlicher Form bei keiner anderen Fakultät oder Hochschule eingereicht.“ Bochum, June 2016 Robert Lemanis ii iii Publication list of the Dissertation 1. Title: A new approach using high-resolution computed tomography to test the buoyant properties of chambered cephalopod shells Authors: R. Lemanis1, S. Zachow2, F. Fusseis3, R. Hoffmann1 Published in Paleobiology in March 2015; Volume 41(02); Pages 313-329 (chapter 3 of this thesis) DOI: 10.1017/pab.2014.17 2. Title: The evolution and development of cephalopod chambers and their shape Authors: R. Lemanis1, D. Korn4, S. Zachow2, E. Rybacki5, R. Hoffmann1 Published in Plos One in March 2016; Volume 11(3) (chapter 4 of this thesis) DOI: 10.1371/journal.pone.0151404 3. Title: Comparative cephalopod shell strength and the role of septum morphology on stress distribution Authors: R. Lemanis1, S. Zachow2, R. Hoffmann1 Under review in PeerJ (chapter 5 of this thesis) 1Institute of Geology, Mineralogy, and Geophysics, Ruhr-Universität Bochum, Bochum, Germany 2Department of Scientific Visualization and Data Analysis, Zuse Institute, Berlin, Germany 3School of Geosciences, University of Edinburgh, Edinburgh, U.K. 4Museum für Naturkunde Berlin, Leibniz-Institut für Evolutions- und Biodiversitätsforschung, Berlin, Germany 5Helmholtz-Zentrum Potsdam, Deutsches GeoForschungsZentrum, Potsdam, Germany iv The research presented here was funded by the Deutsche Forschungsgemeinschaft, grant number HO 4674/2-1. The main applicant for this grant was Dr. R. Hoffmann and the co-applicant was Prof. Dr. S. Zachow. Author contributions and peer review process R.L. = Robert Lemanis, R.H. = René Hoffmann, F.F. = Florian Fusseis, S.Z. = Stephan Zachow, D.K. = Dieter Korn, E.R. = Erik Rybacki. First Article R.L. and R.H. conceived of the study design. R.L. performed the specimen segmentations, processed the tomographic data, designed and performed the calculations, wrote the initial draft including making the figures, and implemented reviewer criticisms. R.H. provided comments to drafts of the manuscript. F.F. was involved in gaining access to the synchrotron facility. S.Z. provided the software used and continual technical support. This article was evaluated by two reviewers, Kenneth De Baets and Dieter Korn, and accepted on October 14, 2014. Second Article R.L. and R.H. designed the study. R.L. performed the specimen segmentations (the pathologic S. spirula, A. scrobiculatus, and Arnsbergites sp. were segmented by students) processed the tomographic data, wrote the initial draft including making the figures, and implemented reviewer criticisms. R.H. and D.K. provided comments through versions of the manuscript. D.K. provided the Arnsbergites sp. specimen. E.R. performed several computed tomographic scans of specimens used in this study. S.Z. provided the software used and continual technical support. This article was submitted twice to Plos One. The first version of the v article was rejected after being reviewed by two reviewers, Kenneth De Baets and one anonymous reviewer. R.L., after discussion with R.H., and D.K., submitted a revised version of the article that was submitted on December 16, 2015. This version was reviewed by two reviewers, Christian Klug and one anonymous reviewer, and accepted on February 26, 2016. Third Article R.L. processed the tomographic data, created and refined the surface and volumetric meshes, performed the finite element analyses, wrote the initial draft including making the figures, and implemented reviewer criticisms. R.H. provided comments to drafts of the manuscript. S.Z. provided the software used and continual technical support. Additional information about this thesis R.L. also contributed to the following publications: Hoffmann et al. 2014 (see references in Chapter 2), Hoffmann et al. 2015 (see references in Chapter 1) and Hoffmann et al. 2015 (see references Chapter 4). An additional project was undertaken as part of the grant that funded this research that resulted in a publication: Lamas-Rodríguez et al. 2015 (see references Chapter 6). References in this thesis are given at the end of their respective chapters. Bochum, June 2016 Robert Lemanis vi vii Abstract Ammonoids are an iconic and highly important fossil group that spans 350 million years and is distributed across the world. The shell of ammonoids has been historically modelled through the use of a number of mathematical descriptors. Investigations into palaeobiological aspects of ammonoids have traditionally been done using these models. This method is capable of recreating the gross morphology of the shell or approximate morphologies of parts of the shell and was used due to the impossibility of modeling the entirety of the shell accurately. The goal of this project is to use computed tomography to create 3D models directly from the original shells and use these models to explore ammonoid palaeobiology. Tomographic based, empirical models of the shells of the deep sea squid Spirula spirula and the Jurassic ammonite Cadoceras are here constructed and used to calculate buoyancy and hydrostatics. Comparisons with traditional methods demonstrate the inaccuracy of previous volume calculations and the biases in hydrostatic calculations. The volume of the Cadoceras shell reconstructed from mathematical approximation shows a persistent underestimation of shell volume. Hydrostatic analysis identified a progressive bias in the calculation of the center of gravity in which overall hydrostatic stability is overestimated for shorter body chamber forms when calculated using the traditional method. Furthermore, a methodology for the calculation of buoyancy using tomographic data is created and used to show that a hypothetical ammonite could remain in the water column despite a potential, overall negative buoyancy. Despite many unknowns, the swimming mode of an ammonite hatchling was reconstructed and found to be very similar to modern coleoid hatchlings. Hypothesis based on mathematical models of ammonoids should be re-evaluated in light of the improved accuracy afforded by computed tomography. viii The function of the complexly folded septa of ammonoids has long been a controversial topic dominated by investigations based on mathematical approximations. Two methods are here used to investigate physiological and mechanical hypothesis of septal function. Ontogenetic changes in the ratio of chamber surface area to volume are calculated based on tomographic data of extant Nautilus, Allonautilus, Spirula, the Paleozoic ammonoids Arnsbergites, and the Mesozoic ammonoids Amauroceras, Cadoceras, and Kosmoceras. Previous work has suggested that septal complexity increased the relative inner surface area of the chambers thereby allowing rapid fluid diffusion out of the chambers. Our results reject this hypothesis over most of ontogeny; however, an increase in the relative surface area of the chambers is shown for all tested ammonoids that preserved their early ontogeny. This might reflect adaptations towards an increase in growth in early ontogeny that are coupled with a shift in early ammonoid evolution towards smaller eggs and higher fecundity. We further demonstrate that the increase in complexity increases the curvature of the septal surface that might aid in chamber refilling. The mechanical function of ammonitic septa is investigated through comparative finite element analysis on the shells of Nautilus, Spirula, and Cadoceras. The entire shell is meshed into finite element models that are subjected to hydrostatic pressure and point loads. The hypothesis that increases in septal complexity should increase shell resistance to hydrostatic pressure is not supported as Spirula, which has the simplest septal morphology, shows the highest resistance to hydrostatic pressure. The use of septal amplitude as a proxy for palaeobathymetry is rejected as increasing septal amplitude is shown to increase the stress due to hydrostatic pressure as opposed to reducing it. Septal amplitude is shown to decrease stress due to point loads indicating a potential anti-predatory function of septal complexity which agrees with the increase in septal curvature that would help compensate for lost shell material. ix Kurzfassung Ammoniten sind sowohl eine ikonische als auch bedeutende Gruppe, deren Geschichte sich über 350 Millionen Jahre erstreckte und deren Fossilien auf der ganzen Welt verbreitet sind. Die Schale dieser Lebewesen wurde mathematisch auf vielfältige Art und Weise beschrieben, die traditionell in paläobiologischen Untersuchungen Anwendung gefunden haben. Diese Methoden können die Bruttomorphologie der Schale oder die ungefähre Morphologie von Teilen der Schale nachbilden und wurden benutzt, da die exakte Darstellung der gesamten Schale unmöglich gewesen ist. Das Ziel