We use scanning electron microscopy imaging to examine the shell microstructure of fossil and living species in five families of caenogastropods (Strombidae, Volutidae, Olividae, Pseudolividae, and Ancillariidae) to determine whether parallel or convergent evolution is responsible for the development of a unique caenogastropod trait, the extreme parietal callus (EPC). The EPC is defined as a substantial thickening of both the spire callus and the callus on the ventral shell surface such that it covers 50% or more of the surface. Caenogastropods as a whole construct the EPC convergently, using a variety of low-density, poorly organized microstructures that are otherwise uncommon in caenogastropod non-callus shell construction. Within clades, however, we see evidence for parallelism in decreased regulation in both the shell and callus microstructure. Low-density and poorly ordered microstructure—such as used for the EPC—uses less organic scaffolding and is less energetically expensive than normal shell microstructure. This suggests the EPC functions to rapidly and inexpensively increase shell thickness and overall body size. Tests of functional ecology suggest that the EPC might function both to defend against crushing predation through increased body size and dissipation of forces while aiding in shell orientation of highly mobile gastropods. These interpretations hinge on the current phylogenetic placement of caenogastropod families, emphasizing the essential contribution of phylogeny when interpreting homoplasy.

中文翻译：

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新生代腹足纲不同群体极端顶叶愈伤组织的收敛性、平行性和功能

我们使用扫描电子显微镜成像来检查 5 个 caenogastropods 家族（Strombidae、Volutidae、Olividae、Pseudolividae 和 Ancillariidae）中化石和活物种的壳微观结构，以确定平行进化还是趋同进化是导致独特的caenogastropod 特征发展的原因，顶叶愈伤组织（EPC）。EPC 被定义为螺旋骨愈伤组织和腹壳表面上的愈伤组织均显着增厚，使其覆盖 50% 或更多的表面。Caenogastropods 作为一个整体构建 EPC，使用各种低密度、组织不良的微结构，这些微结构在 Caenogastropod 非愈伤组织壳结构中并不常见。然而，在进化枝中，我们看到了在壳和愈伤组织微观结构中减少调节的平行性的证据。低密度和不良有序的微结构——例如用于 EPC 的微结构——使用较少的有机支架，并且比正常的壳微结构更便宜。这表明 EPC 的作用是快速且廉价地增加外壳厚度和整体尺寸。功能生态学测试表明，EPC 可能通过增加体型和力量消散来防御粉碎性捕食，同时帮助高度移动的腹足动物的壳定向。这些解释取决于当前 caenogastropod 家族的系统发育位置，强调了系统发育在解释同质性时的重要贡献。这表明 EPC 的作用是快速且廉价地增加外壳厚度和整体尺寸。功能生态学测试表明，EPC 可能通过增加体型和力量消散来防御粉碎性捕食，同时帮助高度移动的腹足动物的壳定向。这些解释取决于当前 caenogastropod 家族的系统发育位置，强调了系统发育在解释同质性时的重要贡献。这表明 EPC 的作用是快速且廉价地增加外壳厚度和整体尺寸。功能生态学测试表明，EPC 可能通过增加体型和力量消散来防御粉碎性捕食，同时帮助高度移动的腹足动物的壳定向。这些解释取决于当前 caenogastropod 家族的系统发育位置，强调了系统发育在解释同质性时的重要贡献。