The varied microstructures of brachiopod biominerals represent a robust archive to understand the evolution and adaptations of marine calcifiers in time. Therefore, a detailed study of the shell microstructure of Cambrian to Devonian brachiopods from Iran is here presented. The shell of 38 brachiopod species, representatives of 22 families and nine orders, has been analysed using scanning electron microscope (SEM), and a database has been built, including macro- and micro-morphological features used to characterize the two- or three-layered brachiopod shells. Two main microstructural variants of the secondary layer have been analysed: fibrous and laminar fabrics. The fibrous layer has a fabric comparable to that of recent brachiopods, whereas the laminar fabric is more complex in its structural organization and has no recent analogue. In cross-section, the laminae are thinner than the fibres, and much less variable in size. There is evidence that taxa with laminar microstructure have diverged from the Billingsellida and then followed a trend implying a decrease in thickness of the laminae. Our linear discriminant analysis (LDA) shows that shell fabric and shell thickness are powerful predictors of shell shapes, which in turn approximate the brachiopod lifestyles and ecological strategies. Taxa with a fibrous fabric are mostly biconvex, whereas the groups with a laminar secondary layer are associated to a variety of shell shapes and lifestyles. Even if the relations between shell fabric and shell thickness remain enigmatic, as well as the metabolic cost they imply, shell fabrics, and the possible structural and mechanical advantages conferred, could have played a role in the evolutionary success of the Strophomenata during the Palaeozoic.

中文翻译：

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古生代腕足动物的外壳结构：图案和趋势

腕足动物生物矿物的各种微观结构代表了一个强大的档案，可以及时了解海洋钙化物的进化和适应。因此，本文对伊朗寒武纪至泥盆纪腕足类动物的壳微结构进行了详细研究。使用扫描电子显微镜（SEM）对代表22科9目38种腕足动物的外壳进行了分析，并建立了数据库，包括用于表征2-3--或3--的宏观和微观形态特征的数据库。层状腕足动物壳。已分析了次要层的两种主要微观结构变体：纤维织物和层状织物。纤维层的织物与最近的腕足动物的织物相当，而层状织物的结构组织更复杂，没有最近的类似物。在横截面中，薄片比纤维更薄，并且尺寸变化更小。有证据表明，具有层状微结构的分类群已经从 Billingsellida 分出，然后趋向于表明层状厚度减少的趋势。我们的线性判别分析 (LDA) 表明，贝壳结构和贝壳厚度是贝壳形状的有力预测因子，进而近似于腕足动物的生活方式和生态策略。具有纤维织物的类群大多是双凸的，而具有层状次层的类群与各种贝壳形状和生活方式有关。即使壳织物和壳厚度之间的关系仍然是个谜，以及它们所暗示的代谢成本，壳织物以及可能赋予的结构和机械优势，