Complexity of septal surfaces and suture lines in ammonoids - implications for the hydrostatic apparatus and palaeoecology using modern CT-techniques

在3.5亿年（下泥盆世-上白垩纪）的菊石演化过程中，从简单到复杂，折叠隔膜的Phragmocon的迭代发展趋势得到了很好的记录。在文献中，讨论了边缘折叠隔膜（=缝合）作用的不同方法。这些主要可以分为生理和机械解释。通过计算腔室体积与内腔室表面的比率，将作为流体静力装置的功能模型与所有其他已知的功能解释进行比较。根据完整的菊石在空心保存（没有沉积物，方解石或黄铁矿的外壳）的变化，该比例是可检测的。它们允许关于不同个体发育阶段的不同生活方式的陈述，以及不同类群之间的比较。数字模型的创建还允许从简单到复杂缝合线的个体发育的具体检查，从而有可能测试在缝合个体发育过程中叶插入的分类学相关模式。作为工作假设，我们假设，最复杂的结构，发现在晚白垩世tetragonitids，包括隔叶和sixlobate主缝合线，与假定的远洋生活方式的陆棚斜坡，最有可能支持的想法，他们提高了效率的流体静力装置作为一个关键的选择因素的设计隔膜。主要目的是证明这个假设是否正确。

In the course of the 350 million years (Lower Devonian-Upper Cretaceous) of ammonoid evolution the iterative trend of development starting with simple to complexly, folded septa of the phragmocon is well documented. In the literature different approaches on the role of marginal folded septa (= suture) are discussed. These can be divided mainly into physiological and mechanical explanations. By the calculations of the ratio of chamber volume against the inner chamber surface the functional model as hydrostatic apparatus is compared against all other known functional interpretations. On the basis of complete ammonites in hollow preservation (no sediment, calcite or pyrite in the shell) changes in that ratio are detectable. They allow statements about different lifestyles in different ontogenetic stages, and comparisons between different taxa. The creation of digital models also allows the specific examination of ontogenetic development from simple to complex sutures and thus the possibility to test for the taxonomic relevant mode of lobe insertion during sutural ontogeny. As working hypothesis we assume that the most complex structures found in late Cretaceous tetragonitids including the septal lobe and a sixlobate primary suture, in conjunction with presumed pelagic lifestyles on the shelf slope, most likely support the idea that they improve the efficiency of the hydrostatic apparatus as a key selection factor for the design of the septa. It is the main goal to prove whether or not this hypothesis is correct.