Brachiopod shell thickness links environment and evolution

While it is well established that the shapes and sizes of shells are strongly phylogenetically controlled, little is known about the phylogenetic constraints on shell thickness. Yet, shell thickness is likely to be sensitive to environmental fluctuations and has the potential to illuminate environmental perturbations through deep time. Here we systematically quantify the thickness of the anterior brachiopod shell which protects the filtration chamber and is thus considered functionally homologous across higher taxa of brachiopods. Our data comes from 66 genera and ten different orders and shows well-defined upper and lower boundaries of anterior shell thickness. For Ordovician and Silurian brachiopods we find significant order-level differences and a trend of increasing shell thickness with water depth. Modern (Cenozoic) brachiopods, by comparison, fall into the lower half of observed shell thicknesses. Among Ordovician – Silurian brachiopods, older stocks commonly have thicker shells, ...尽管已有明确研究证实壳体的形态与大小受系统发育的强烈调控，但目前学界对壳体厚度所受的系统发育限制仍知之甚少。然而，壳体厚度大概率对环境波动极为敏感，且具备为深时 (deep time) 尺度下的环境扰动研究提供新见解的潜力。本研究系统量化了腕足动物 (brachiopod) 的前壳体厚度——该壳体包裹滤食腔，在腕足动物的高级分类单元中被认为具有功能同源性。本次研究的数据涵盖66个属与10个不同的目，结果清晰界定了前壳体厚度的上下限范围。针对奥陶纪 (Ordovician) 与志留纪 (Silurian) 的腕足动物，本研究发现其壳体厚度存在显著的目级差异，且壳体厚度随水深增加而增大的演化趋势。相比之下，现代（新生代，Cenozoic）腕足动物的壳体厚度大多处于观测范围的下半区间。在奥陶纪-志留纪的腕足动物中，更为古老的类群通常拥有更厚的壳体……