Hydromechanical Constraints on the Ontogeny and Evolution ofScaphitid Ammonites

我们计划从它们的系统发育框架和它们在时间、岩相和地理上的分布的背景下，研究与它们密切相关的一组舟形虫菊石的水力学性质。我们选择了一个特有的单系类群，大约有25种，范围从北美洲西部内陆的都罗尼亚到桑托尼亚(上白垩纪)。这些物种在它们的贝壳中保存着它们生长的记录，并在个体发育过程中表现出深刻的形态变化，最终在成熟时形成一个未盘绕的身体腔。此外，这些物种在成体贝壳形状上表现出广泛的多样性，从相对扁平的物种和相对凹陷的物种不等，前者的体腔发育良好，后者的体腔通常是盘绕的。利用流动水箱和阻力测量仪器，我们将研究个体发育变化对每个物种的大小和形状的流体力学影响。这将使我们能够构建涵盖所有胚胎后生长的物种特有的流体力学个体发生轨迹(HOT)。我们将通过对虹吸虫和隔虫的研究来补充这些信息，这可能会提供相对栖息地深度的信息。我们将把这些热点与各自物种在西部内海记录良好的背景下的古环境和进化分布进行比较。因此，这种比较将首次阐明功能性流体力学约束对一组密切相关的菊石的演化和地理分布的影响程度和方式。

We plan to investigate the hydromechanical properties of closely related group of scaphitid ammonite species in the context of their phylogenetic framework and their distribution with respect to time, lithofacies, and geography. We have chosen an endemic, monophyletic group of approximately 25 species ranging from the Turonian to Santonian (Upper Cretaceous) of the Western Interior of North America. These species preserve in their shells a record of their growth and manifest profound morphological changes during ontogeny, eventually developing an uncoiled body chamber at maturity. In addition, these species display a wide diversity in adult shell shape ranging from relatively compressed species with a well-developed "scaphitid" body chamber to relatively depressed species in which the body chamber is "normally" coiled. Using a flow tank and drag measuring apparatus, we will study the hydromechanical implications of ontogenetic changes in size and shape for each species. This will allow us to construct species specific hydromechanical ontogenetic trajectories (HOT's) covering all of postembryonic growth. We will supplement this information with studies of the siphuncle and septa, which may provide information on relative habitat depth. We will compare these HOT's with the paleoenvironmental and evolutionary distribution of the respective species within the well documented context of the Western Interior Seaway. Thus, this comparison will elucidate for the first time the extent and way in which functional hydromechanical constraints have contributed to the evolution and geographic distribution of a closely related group of ammonites.