Arthropods (i.e. insects, spiders, crustaceans, myriapods and others), are the most successful Phanerozoic animals. The group is characterized by the possession of a segmented body, jointed limbs and a hard cuticle that is episodically moulted. One highly successful but now extinct group of arthropods is the trilobites. Trilobites underwent episodic moulting (ecdysis), and most trilobites possess facial sutures, lines of weakness in the cephalon, via which the exuviae is shed and the animal emerges. However, zones of weakness appear to represent a structural trade-off or constraint, particularly during burrowing; sacrificing a consolidated head region useful in burrowing for the ability to moult. Here we reconcile this trade-off by using biomechanical modelling to demonstrate that facial sutures exist in regions of low stress during the application of burrowing loads. Furthermore, facial sutures and the structure of the cephalon enable sutured trilobites to withstand greater stresses than their non-suture counterparts. We suggest that this ability to withstand greater burrowing loads enabled trilobites to successfully invade bioturbated and more consolidated sediments of the Cambrian Sediment Revolution, thus facilitating their diversification in the Cambrian and Ordovician and contributing to the evolutionary success of this iconic arthropod group.

中文翻译：

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头部生物力学是三叶虫进化成功的基础

节肢动物（即昆虫、蜘蛛、甲壳类、多足类等）是显生宙最成功的动物。该群体的特点是拥有一个分段的身体、关节四肢和一个偶尔蜕皮的坚硬角质层。三叶虫是一种非常成功但现已灭绝的节肢动物。三叶虫经历了间歇性蜕皮（蜕皮），并且大多数三叶虫具有面部缝合线，头骨中的弱线，通过这些线，蜕皮脱落并且动物出现。然而，弱点似乎代表了一种结构性的权衡或约束，特别是在挖洞期间；牺牲一个巩固的头部区域，用于挖洞以换取换羽能力。在这里，我们通过使用生物力学模型来证明在应用挖洞载荷期间面部缝合线存在于低应力区域，从而调和了这种权衡。此外，面部缝合线和头颅的结构使缝合的三叶虫能够承受比未缝合的三叶虫更大的压力。我们认为，这种承受更大挖洞负荷的能力使三叶虫能够成功侵入寒武纪沉积物革命中生物扰动和更坚固的沉积物，从而促进它们在寒武纪和奥陶纪的多样化，并有助于这一标志性节肢动物群的进化成功。