Data from: Assessing the evolutionary history of the class Synurophyceae (Heterokonta) using molecular, morphometric, and paleobiological approaches

Premise of the study: Heterokont algae of the class Synurophyceae, characterized by distinctive siliceous scales that cover the surface of the cell, are ecologically important in inland waters, yet their evolutionary history remains enigmatic. We explore phylogenetic relationships within this group of algae relative to geologic time, with a focus on evolution of siliceous components. Methods: We combined an expansive five-gene and time-calibrated molecular phylogeny of synurophyte algae with an extensive array of fossil specimens from the middle Eocene to infer evolutionary trends within the group. Key results: The group originated in the Jurassic approximately 157 million years ago (Ma), with the keystone genera Mallomonas and Synura diverging during the Early Cretaceous at 130 Ma. Mallomonas further splits into two major subclades, signaling the evolution of the V-rib believed to aid in the spacing and organization of scales on the cell covering. Synura also diverges into two primary subclades, separating taxa with forward-projecting spines on the scale from those with a keel positioned on the scale proper. Approximately one third of the fossil species are extinct, whereas the remaining taxa are linked to modern congeners. Conclusions: The taxonomy of synurophytes, which relies extensively on the morphology of the siliceous components, is largely congruent with molecular analyses. Scales of extinct synurophytes were significantly larger than those of modern taxa and may have played a role in their demise. In contrast, many fossil species linked to modern lineages were smaller in the middle Eocene, possibly reflecting growth in the greenhouse climatic state that characterized this geologic interval.研究背景：隶属于硅鳞金藻纲（Synurophyceae）的异鞭藻类（Heterokont algae），以覆盖细胞表面的独特硅质鳞片为典型特征，在内陆水域中具有重要生态意义，但其演化历史仍属未解之谜。本研究围绕该类藻类的系统发育关系与地质时序展开探究，重点关注其硅质结构的演化历程。 研究方法：本研究结合涵盖5个基因的时间校准分子系统发育分析与大量中始新世时期的化石标本，对该类群的演化趋势进行推演。 主要结果：该类群起源于约1.57亿年前（Ma）的侏罗纪，其核心属马甲藻属（Mallomonas）与合尾藻属（Synura）于1.3亿年前（Ma）的早白垩世发生分化。马甲藻属进一步分化为两个主要亚支，这标志着被认为可辅助细胞被膜上鳞片排布与结构组织的V形肋的演化。合尾藻属同样分化为两个主要亚支，将鳞片带有前伸棘突的类群与鳞片本体带有龙骨突的类群区分开来。约三分之一的化石物种已灭绝，其余类群则与现生同属物种存在关联。 研究结论：硅鳞金藻类的分类学研究高度依赖硅质结构的形态特征，其分类结果与分子分析结果整体一致。已灭绝的硅鳞金藻类的鳞片尺寸显著大于现生类群，这可能与其灭绝存在关联。与之相反，诸多与现生支系相关联的化石物种在中始新世时期体型更小，这或许反映了该地质时段以温室气候为特征的环境下的体型演化趋势。