Hydrodynamic trade-offs in potential swimming efficiency of planispiral ammonoids
Hydrodynamic trade-offs in potential swimming efficiency of planispiral ammonoids
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DOI：
10.1017/pab.2022.13
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发表时间：
2023-01-09
期刊：
影响因子：
2.7
通讯作者：
Hebdon，Nicholas
中科院分区：
文献类型：
--
作者：
Ritterbush，Kathleen Anita;Hebdon，Nicholas
在数亿年的时间里，菊石类头足类动物是地球上最丰富的海洋食肉动物，但它们可能的游泳能力范围并不受限制。我们调查潜在的流体动力学成本和不同的海螺几何形状，使用计算流体动力学模拟提供的优势。原始阻力的模拟表明，预期的增加速度和海螺通货膨胀，与已发表的实验数据一致。在不同尺度的水湍流（通过雷诺数）的分析揭示了海螺形状，大小和速度之间的动态权衡。在压缩壳体中，脐带缆暴露的成本在小尺寸（和/或低速度）时差别不大，但在大尺寸（和/或高速度）时差别很大。我们估计，小型菊石每秒可以移动一到三个直径（即，直径为5厘米的典型菊石的速度可达5 - 15厘米/秒），但大型菊石的速度差异更大（10厘米的蛇锥可能低于30厘米/秒，而10厘米的氧锥可能达到40厘米/秒）。所有这些速度都只适用于喷射推进的短暂爆发，持续时间只有几秒钟，以躲避捕食者或同种对手。这些分析不包括系统发育、分类、二级海螺结构（肋骨、装饰等），或内部解剖结构的流体静力学后果（软体、缝合复杂性）。对于特定的古生态背景下，我们认为这些结果如何告知我们的重建侏罗纪菊石恢复从三叠纪末的大规模灭绝。更大的改进将伴随着额外的模拟，这些模拟测量了在单个喷气运动期间，个人形状特征变化、装饰和细微的身体延伸如何影响增加的质量。
Ammonoid cephalopods were Earth's most abundant oceanic carnivores for hundreds of millions of years, yet their probable range of swimming capabilities is poorly constrained. We investigate potential hydrodynamic costs and advantages provided by different conch geometries using computational fluid dynamics simulations. Simulations of raw drag demonstrate expected increases with velocity and conch inflation, consistent with published experimental data. Analysis at different scales of water turbulence (via Reynolds number) reveals dynamic trade-offs between conch shape, size, and velocity. Among compressed shells, the cost of umbilical exposure makes little difference at small sizes (and/or low velocity) but is profound at large sizes (and/or high velocity). We estimate that small ammonoids could travel one to three diameters per second (i.e., a typical ammonoid with a 5-cm-diameter shell could travel 5–15 cm/s), but that large ammonoids faced greater discrepancies (a 10 cm serpenticone likely traveled <30 cm/s, while a 10 cm oxycone might achieve >40 cm/s). All of these velocities are proposed only for short bursts of jet propulsion, lasting only a few seconds, in the service of dodging a predator or conspecific rival. These analyses do not include phylogeny, taxonomy, second-order conch architecture (ribs, ornament, etc.), or hydrostatic consequences of internal anatomy (soft body, suture complexity). For specific paleoecological context, we consider how these results inform our reconstruction of Jurassic ammonite recovery from the end-Triassic mass extinction. Greater refinements will come with additional simulations that measure how added mass is influenced by individual shape-trait variations, ornament, and subtle body extensions during a single jet motion.