Hydromechanical Constraints on the Ontogeny and Evolution ofScaphitid Ammonites

我们计划研究的流体力学性能的 在上下文中密切相关的一组舟形菊石物种 它们的系统发育框架和它们的分布 时间岩相和地理 我们选择了一种特有的， 一个单系群，约有25种， 西部内陆的Turonian至Santonian（上白垩纪） 北美的一部分。 这些物种在壳里保存着 它们的生长和表现出深刻的形态变化， 个体发育，最终发育成一个展开的体腔， 成熟 此外，这些物种在以下方面表现出广泛的多样性： 成虫的壳形从相对扁平的种到 一个发育良好的“舟骨”体腔， 体腔“正常”盘绕的物种。 使用 流动槽和阻力测量装置，我们将研究 个体发育的大小变化的流体力学影响， 每个物种的形状。 这将使我们能够构建物种 特定的水力机械个体发育轨迹（HOT）， 都是胚后发育的产物 我们将补充这些信息 通过对管风琴和隔膜的研究， 关于相对生境深度的信息。 我们将比较这些热门的 与古环境和演化分布 在有据可查的背景下的各个物种 西部内陆航道。 因此，这种比较将阐明 这是第一次，功能的范围和方式， 流体力学的限制促成了这种演变， 与菊石类关系密切的一个地理分布群。

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.