Evolutionary and developmental patterns of Cretaceous uncoiled ammonites

异形菊石（即，在盘绕上偏离平螺旋、规则盘绕的菊石）属于最神秘的化石群，但它们的起源、古生物学和功能形态学仍然是一个有争议的问题。很少知道可能的原因，为什么氨气迭代偏离正常的盘绕，而不是实现一个假定的不利的海螺结构，就浮力控制和运动。此外，就分类多样性和形态差异而言，特别是在白垩纪，它们成为成功的分支的原因知之甚少。在拟议的项目中，这些展开的菊石将通过使用相关特征（如海螺几何形状、贝壳装饰和缝合线）来分析它们的形态空间占用。选择白垩纪的分类群（取决于材料的可用性）将被研究，包括可能的性别二态性，种内变异性和个体发生性状的变异。其广泛的地理分布、丰富的丰度、快速的进化速度，以及由于壳的增生生长而保存了整个个体发育，使中生代菊石成为研究古生态扰动演化情景的完美化石类群。本项目的主要目标是：(1)验证白垩纪异型菊石起源的各种假说；(2)评价高等分类实体的种属概念、有效性及其系统发育关系；(3)研究古生态参数及其对海螺几何形状的可能影响；(4)比较个体发育特征的多样性和差异模式。本文首次分析了白垩纪异形菊石的种内变异性，并讨论了它们在盘绕和螺形上与单形菊石的偏差。通过本研究，我们将提高对白垩纪卷状菊石的系统发育关系、古生物学、古生态学和地层范围的认识。白垩纪以海侵/海退、变暖/变冷事件和海洋缺氧事件为特征，为研究特定异形壳形态的出现和分布提供了理想条件，并有望发现特征模式。与同时期沉积的正常盘绕的菊石相比，可以测试不同的古环境变化（水深、温度、氧气）及其对异质壳几何形状的影响。

The heteromorph ammonoids (i.e., ammonoids that deviate in their coiling from the planispiral, regular coiling) belong to the most enigmatic fossil groups, but their origin, palaeobiology, and functional morphology is still a matter of debate. Little is known about possible reasons why ammonoid iteratively deviated from normal coiling and instead realise a putatively disadvantageous conch construction with respect to buoyancy control and locomotion. Furthermore little is known why they became successful clades in terms of taxonomic diversity and morphological disparity especially during the Cretaceous. Within the proposed project, these uncoiled ammonoids will be analysed with respect to their morphospace occupation by the use of relevant characters such as conch geometry, shell ornamentation, and suture line. Selected taxa (depending on availability of material) from the Cretaceous will be studied including possible sexual dimorphism, intraspecific variability, and variation in ontogenetic traits. Their wide geographical distribution and high abundances, fast evolutionary rates, and the preservation of the entire ontogeny due to accretionary shell growth made especially Mesozoic ammonoids a perfect fossil group to study evolutionary scenarios with respect to palaeoecological perturbations. The main goal of this project is (1) to test various hypotheses of the origin of Cretaceous heteromorph ammonites, (2) to evaluate the species and genus concepts as well as validity of higher taxonomic entities and their phylogenetic relationships, (3) to investigate palaeoecological parameters and their possible influence on the conch geometry, and (4) to compare diversity and disparity patterns with respect to ontogenetic traits. Here we make a first attempt to analyse the intraspecific variability of Cretaceous heteromorph ammonites and discuss them with respect to their deviation in coiling and conch form from monomorph ammonoids. With this study we will improve the understanding of the phylogenetic relationships, palaeobiology, palaeoecology, and stratigraphic range of the Cretaceous uncoiled ammonites. The Cretaceous period is characterised by transgressions/regressions, warming/cooling events and oceanic anoxic events which made it ideal to study the appearance and distribution of specific heteromorph shell morphologies and hopefully detected characteristic patterns. In comparison with normally coiled ammonites from contemporaneous deposits the influence of distinct palaeoenvironmental changes (water depth, temperature, oxygen) and their effect on the heteromorph shell geometry can be tested.