ABSTRACT

The biomechanics of uncoiled heteromorph ammonoids with body chambers that terminate in U-shaped hooks (ancylocones) were investigated with virtual and physical models of Audouliceras renauxianum. Virtual models were used to compute the hydrostatic properties of this morphotype. Audouliceras has the capacity for neutral buoyancy and this suggests that other taxa with similar proportions had this ability as well. Hydrostatic stability gradually increases during ontogeny, coincident with the larger degree of uncoiling. The juvenile planispiral stage has a similar stability and apertural orientation to the extant Nautilus. The adult stage, however, undergoes an increase in stability by a factor of over 3, while assuming an upward-facing posture. Counterintuitively, the stage during the formation of the shaft (before the growth of the U-shaped hook) is oriented horizontally. This intermediate stage would have had poor horizontal mobility due to the positioning of the hyponome below the centre of mass. The juvenile planispiral stage and mature stage, however, would have been well suited to horizontal backward movement with minimal rocking. Ancylocones are generally thought of as quasiplanktic vertical migrants. Thus, their relative horizontal swimming ability has been largely disregarded. Experiments on 3D printed, neutrally buoyant physical models reveal that hydrodynamic drag is indeed larger compared to Nautilus. However, Audouliceras could reach similar maximum horizontal velocities depending on the available thrust. Sepia-like thrusts yield velocities similar to equivalently sized Nautilus (c. 15 cm/s), while Nautilus-like thrusts yield velocities not much lower (c. 11 cm/s). Due to the hydrostatic properties of the ancylocone, the adult model undergoes less rocking (±4.5°) during movement than Nautilus (±10°). The minimal hydrodynamic consequences for ancylocones suggest that stability, orientation and directional efficiency are key selective pressures for some heteromorph shells, which may have primarily served as hydrostatic devices.

中文翻译：

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稳定的钩子：具有U形体腔的异形氨化物的生物力学

摘要

用真假拟金藻的虚拟和物理模型研究了未卷曲异形氨化物的生物力学，其具有以U形钩（雄激素）终止的体室。使用虚拟模型来计算该形态型的静水特性。Audouliceras具有中性浮力的能力，这表明其他具有相似比例的类群也具有这种能力。在本体形成过程中，静液压稳定性逐渐增加，与较大程度的开卷同时发生。幼年的平面螺旋阶段具有与现存的鹦鹉螺类似的稳定性和开孔方向。然而，成年阶段的稳定性增加了3倍以上，同时呈现出朝上的姿势。与直觉相反，在杆身形成过程中的阶段（在U形钩的增长之前）是水平定向的。由于该次检波器位于质心下方，因此该中间阶段的水平移动性较差。然而，幼年的平面螺旋阶段和成年阶段将非常适合于水平向后运动，并且摇摆最小。一般将脂环酮视为准浮游性垂直移民。因此，它们的相对水平游泳能力已被大大忽略。在3D打印的中性浮力物理模型上进行的实验表明，与Nautilus相比，流体动力阻力确实更大。然而，Audouliceras可以达到类似的最大水平速度，具体取决于可用的推力。棕褐色样推力产生类似的速度，以相等大小的鹦鹉螺（℃。 15厘米/秒），而鹦鹉螺样推力产生的速度不是非常低（℃。 11厘米/秒）。由于洋基香豆素的静水性能，成年模型在运动过程中的晃动（±4.5°）比鹦鹉螺（±10°）小。对对映体的最小流体动力学结果表明，稳定性，取向和定向效率是某些异形壳的关键选择压力，这些壳可能主要用作静水装置。