Morphological function of trace fossil Paleodictyon: An approach from fluid simulation
Morphological function of trace fossil Paleodictyon: An approach from fluid simulation
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DOI：
10.2517/pr210001
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发表时间：
2022-10-01
影响因子：
0.9
通讯作者：
Naruse, Hajime
中科院分区：
文献类型：
--
作者：
Kikuchi, Kazuki;Naruse, Hajime
本文从计算流体力学的角度研究了古dictyon的功能形态。现代标本显示出一种独特的形态，由六边形网状结构、向海底开放的垂直竖井和海底上的盾状丘组成。在一些化石样本中也保留了竖井的痕迹。为了解释它们的特征形态，人们提出了一种“被动通风”假说，认为它们的功能是通过提供含氧水和食物的海底水流为洞穴通风。然而，这一假设尚未得到证实。本研究利用古dictyon三维几何形态的计算流体动力学模型和估算洞穴通风效率，进行了数值实验，以了解该鱼化石所形成的结构的功能。结果表明，海水在土墩边缘区域的竖井中流动，并从土墩顶部的竖井流出，流经网格结构。这种通风现象只有在古狄古统有盾状丘的情况下才会出现。随着底流流速的增大，通风量迅速增大。与此相反，随着盾状土墩的高度增加，速率也随之增加，而在4 mm高度出现小峰值后，速率一度下降，这与现代标本中测量的值相对应。这种巧合可能意味着，在现代标本中观察到的土丘高度是通风效率和抗侵蚀物理稳定性之间平衡的优化结果。在这个土丘高度，通过通风在网状结构中充分交换水分只用了不到几分钟的时间，这大概足以满足古dictyon生产者的能力。
This study examined the functional morphology of the trace fossil Paleodictyon in terms of computational fluid dynamics. The modern specimens show a unique morphology that is composed of a hexagonal mesh structure, vertical shafts opening to the seafloor, and a shield-like mound on the seafloor. The traces of the vertical shafts were also preserved in some fossil examples. To explain their characteristic morphology, a "passive ventilation" hypothesis has been proposed suggesting that their function was to ventilate their burrows with bottom currents, which supply both oxygenated water and food. However, this hypothesis has not yet been verified. This study conducted numerical experiments to understand the functions of the structures created by this ichnofossil by using a model of computational fluid dynamics with the 3D geometry of Paleodictyon and estimating the efficiency of the ventilation in burrows. As a result, it was observed that seawater flowed in the vertical shafts in the marginal area of the mound, and flowed out from the shafts located on the top of the mound, flowing through the mesh structure. This ventilation was observed only in the case that Paleodictyon had a shield-like mound. The ventilation rate rapidly increased as the bottom current velocity increased. In contrast, the rate also increased with the height of the shield-like mounds, whereas it once dropped after the minor peak at 4 mm in height, which corresponds to the value measured in the modern specimens. This coincidence may imply that the height of the mound observed in modern specimens resulted from the optimization in balancing between the efficiency of ventilation and physical stability against erosion. Full exchange of water in the mesh structure by ventilation took less than a few minutes at this mound height, which is presumably sufficient for the ability of Paleodictyon producers.