Colonization of the water column by animals occurred gradually during the early Palaeozoic. However, the morphological and functional changes that took place during this colonization are poorly understood. The fossil record provides clear evidence of animals that were well adapted for swimming near the seafloor or in the open ocean, but recognising transitional forms is more problematic. Trilobites are a good model to explore the colonization of marine ecosystems. Here, we use computational fluid dynamics (CFD) to test between competing functional hypotheses in the Ordovician trilobite Placoparia. The CFD simulations exhibits hydrodynamics that promote detachment from the seafloor but also promote return to the seafloor following detachment, this is compatible with hopping locomotion. The results suggest that Placopara was not able to swim, but its hydrodynamics allowed it to hop long distances. This is consistent with the fossil record, as some ichnofossils show evidence of hopping. This type of locomotion could be useful to avoid predators as an escape mechanism. In addition, CFD simulation shows how the morphology of Placoparia is adapted to protect anterior appendices of the trunk and generate a ventral vortex that send food particles directly to the trilobite mouth. Adaptations in Placoparia allowed the first steps to evolved a new ecological habitat and consequently nektonization during the GOBE.

在古生代早期，动物对水柱的殖民逐渐发生。然而，人们对这种殖民化过程中发生的形态和功能变化知之甚少。化石记录提供了非常适合在海底附近或公海中游泳的动物的明确证据，但识别过渡形式更成问题。三叶虫是探索海洋生态系统殖民化的好模型。在这里，我们使用计算流体动力学 (CFD) 来测试奥陶纪三叶虫Placoparia 中相互竞争的功能假设。CFD 模拟展示了促进从海底脱离但也促进脱离后返回海底的流体动力学，这与跳跃运动兼容。结果表明Placopara不会游泳，但它的流体动力学允许它长距离跳跃。这与化石记录一致，因为一些化石化石显示了跳跃的证据。这种类型的运动可能有助于避免作为逃生机制的捕食者。此外，CFD 模拟显示了Placoparia的形态如何适应保护躯干的前阑尾并产生腹侧涡流，将食物颗粒直接发送到三叶虫口中。Placoparia 的适应使得在 GOBE 期间进化出一个新的生态栖息地和随后的 nektonization 迈出了第一步。