Morphology permits the extracting of information to study patterns of disparity and diversity of a particular group of animals through time. Enrolment is a characteristic behaviour of trilobites, having been first recorded in the Cambrian and continued until their demise at the end of Permian mass extinction. Morphological trends related to enrolment strategies have been documented previously but are yet to have been analysed in a morphospace framework. Here we analyse the cephalic shape of a wide range of trilobite taxa using geometric morphometrics. These methodologies were implemented to explore whether the relationship between the shape of the head and the evolution of different enrolment styles correspond with an increase in morphospace or disparity during the Palaeozoic. Our results show distinct patterns of diversity and disparity in the functional morphology of trilobites during the Palaeozoic. Furthermore, these analyses show that enrolment types in trilobites without interlocking devices (e.g. cylindrical) permit more flexibility in the head shape, promoting higher rates of disparity, possibly leading to an enhanced ability to occupy a broad range of ecological niches. On the contrary, lower disparity cephalic shape constrains the way to enclose the body and consequently places limitations on the ability to adapt to new niches. Our results indicate that the higher rates of morpho-functional diversity and disparity coincide with the increase of morphospace in radiations in the early Palaeozoic (Cambrian and Ordovician) but also immediately after the Carboniferous-Permian biodiversification event. Low disparity rates constrain the success of trilobites with a specific enrolment type. Finally, the results show that sphaeroidal enrolment style was the most successful type that evolved independently in all trilobite orders.

中文翻译：

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三叶虫头颅的形态多样性和差异以及整个古生代三叶虫登记的演变

形态学允许提取信息以研究特定动物群随时间的差异和多样性模式。登记是三叶虫的一种特征行为，它首先记录在寒武纪，并一直持续到它们在二叠纪大灭绝结束时灭绝。与招生策略相关的形态学趋势之前已被记录，但尚未在形态空间框架中进行分析。在这里，我们使用几何形态学分析了各种三叶虫类群的头部形状。实施这些方法是为了探索头部形状与不同招生方式演变之间的关系是否与古生代形态空间或差异的增加相对应。我们的研究结果显示了古生代三叶虫功能形态的多样性和差异的明显模式。此外，这些分析表明，没有联锁装置（例如圆柱形）的三叶虫的登记类型允许头部形状更具灵活性，促进更高的差异率，可能导致增强占据广泛生态位的能力。相反，较低差异的头部形状限制了包围身体的方式，因此限制了适应新生态位的能力。我们的研究结果表明，较高的形态功能多样性和差异率与早古生代（寒武纪和奥陶纪）辐射中形态空间的增加相吻合，而且在石炭纪-二叠纪生物多样化事件之后也立即出现。低差异率限制了具有特定注册类型的三叶虫的成功。最后，结果表明，在所有三叶虫目中，球状登记方式是最成功的独立进化类型。