The seemingly aberrant coiling of heteromorphic ammonoids suggests that they underwent more significant changes in hydrostatic properties throughout ontogeny than their planispiral counterparts. Such changes may have been responses to different selective pressures at different life stages. The hydrostatic properties of three species of Didymoceras (D. stevensoni, D. nebrascense, and D. cheyennense) were investigated by creating virtual 3D models at several stages during growth. These models were used to compute the conditions for neutral buoyancy, hydrostatic stability, orientation during life, and thrust angles (efficiency of directional movement). These properties suggest that Didymoceras and similar heteromorphs lived low-energy lifestyles with the ability to hover above the seafloor. The resultant static orientations yielded a downward-facing aperture in the hatchling and a horizontally facing aperture throughout most of the juvenile stage, before terminating in an upward direction at maturity. Relatively high hydrostatic stabilities would not have permitted the orientation of Didymoceras to be considerably modified with active locomotion. During the helical phase, Didymoceras would have been poorly suited for horizontal movement, yet equipped to pirouette about the vertical axis. Two stages throughout growth, however, would have enhanced lateral mobility: a juvenile stage just after the formation of the first bend in the shell and the terminal stage after completion of the U-shaped hook. These two more mobile phases in ontogeny may have improved juvenile dispersal potential and mate acquisition during adulthood, respectively. In general, life orientation and hydrostatic stability change more wildly for these aberrantly coiled ammonoids than their planispiral counterparts.

中文翻译：

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疯狂的方法：Didyoceras（Nostoceratidae：Ammonoidea）流体静力学特性的个体发生变化

异形菊石的看似异常的盘绕表明，它们在整个个体发育过程中的流体静力学特性比它们的平面螺旋对应物经历了更显着的变化。这种变化可能是对不同生命阶段不同选择压力的反应。三种水的静水性能双角龙(D.史蒂文森尼,D. nebrascense， 和D. cheennense) 通过在生长过程中的几个阶段创建虚拟 3D 模型进行研究。这些模型用于计算中性浮力、流体静力稳定性、寿命期间的定向和推力角（定向运动的效率）的条件。这些性质表明双角龙和类似的异形体过着低能量的生活方式，能够在海底盘旋。由此产生的静态方向在幼体中产生了一个向下的孔，在幼年的大部分时间里产生了一个水平的孔，然后在成熟时以向上的方向终止。相对较高的流体静力学稳定性不允许双角龙通过主动运动进行相当大的修改。在螺旋阶段，双角龙本来不适合水平运动，但可以绕垂直轴旋转。然而，整个生长过程中的两个阶段会增强横向移动性：在壳中第一个弯曲形成后的幼年阶段和完成 U 形钩后的终末阶段。个体发育中的这两种更多的流动相可能分别提高了成年期的幼年传播潜力和配偶获取。一般来说，这些异常盘绕的菊石的生命方向和流体静力稳定性的变化比它们的平面螺旋对应物更剧烈。