Analyzing the mechanical consequences of septal complexity in ammonites

Ammonoids是一种灭绝的头足类动物，跨越3.5亿年，分布在世界各地的海洋。这些动物的生态学已被用来重建古环境，宏观演化趋势，并解释地球化学数据。然而，它们的大部分生态学还没有得到很好的理解，特别是栖息地的深度，这通常与高度弯曲和多裂片的隔膜的复杂形态有关。有假说认为，这些结构的复杂性增加有助于增加壳的不同部分对由于静水压力增加而内爆的抵抗力，从而使具有更复杂缝合线的形式栖息在更深的沃茨。隔膜的这种机械功能的证据仅限于理论力学模型，其结果直接相互矛盾。一项研究认为，间隔的复杂性削弱了壳对内爆，而另一项研究认为，间隔的复杂性加强了壳对内爆。该项目将结合联合收割机纳米机械材料测试、高分辨率计算机断层扫描和有限元分析，系统地研究菊石壳的经验力学模型，以确定隔膜的复杂形态是否增强了壳抵抗外部载荷的能力。头足类动物外壳的机械性能将在受控的湿度和温度下使用纳米压痕进行测试。该数据将与nano-CT衍生的3D模型相结合，以便进行有限元分析，以测试先前存在的间隔功能假设。这项工作将有助于确定是否复杂的隔膜形态独特的菊石反映了他们的生态方面。了解隔膜的功能将影响我们的解释：菊石古生物学，进化趋势，菊石的持久性，通过质量迁移，并提供现实的价值为潜在的栖息地深度限制，这将影响来自菊石壳的地球化学数据的解释。

Ammonoids are an extinct group of cephalopods that span 350 million years and were distributed across the world's oceans. The ecology of these animals has been used to reconstruct palaeoenvironment, macroevolutionary trends, and interpret geochemical data. However, much of their ecology is not well understood, specifically habitat depth, which is often connected to the complex morphology of the highly curved and multi-lobate septa. Hypotheses argue that the increased complexity of these structures helped to increase the resistance of different parts of the shell to implosion due to increasing hydrostatic pressure, thus allowing forms with more complex sutures to inhabit deeper waters. Evidence of this mechanical function of the septa is limited to theoretical mechanical models, the results of which have directly contradicted each other. One study argued that septal complexity weakens the shell against implosion while another argued septal complexity strengthens the shell against implosion. This project will combine nano-mechanical material testing, high-resolution computed tomography and finite element analysis to systematically study empirical, mechanical models of ammonoid shells to determine whether the complex morphology of the septa strengthen the shell against external loads. The mechanical properties of the shells of cephalopods will be tested using nanoindentation under controlled humidity and temperatures. This data will be combined with nano-CT derived 3D models in order to perform finite element analyses to test the pre-existing hypotheses of septal function. This work will help determine whether the complex septal morphology unique to ammonoids reflects aspects of their ecology. Understanding the functions of the septa will influence our interpretation of: ammonoid paleobiology, evolutionary trends, the persistence of ammonoids through mass extinctions, and provide realistic values for potential habitat depth limits, which will affect the interpretation of derived geochemical data from ammonite shells.