State Key Laboratory of Continental Dynamics, Shaanxi Key Laboratory of Early Life and Environments and Department of Geology, Northwest University, Xi'an, 710069, China.
Department of Palaeobiology, Swedish Museum of Natural History, Box 50007, 104 05, Stockholm, Sweden.
BMC Ecol Evol. 2022 May 17;22(1):64. doi: 10.1186/s12862-022-02022-9.
A small hyolith, with a triangular operculum and a conical-pyramidal conch with a sharp apex, originally documented as Ambrolinevitus ventricosus, is revised based on new material from the Chengjiang biota. The operculum of 'Ambrolinevitus' ventricosus displays strong morphological similarities with the operculum of Paramicrocornus from the Shuijingtuo Formation (Cambrian Series 2), indicating that the species should be reassigned to Paramicrocornus.
Based on the unusual morphology of Paramicrocornus, we herein propose a new family Paramicrocornidae fam. nov. A cladistic analysis of Cambrian and Ordovician hyoliths clearly delineates hyolithids as a monophyletic group which evolved from the paraphyletic orthothecids in the early Cambrian and with Paramicrocornidae as its closest relative.
The phylogenetic analysis, together with the distribution of hyoliths from the Cambrian to the Ordovician, reveals the presumptive evolution model of both the skeleton and soft-part anatomy of hyoliths. The Family Paramicrocornidae plays an intermediate role in hyolith evolution, representing the transitional stage in the evolution from orthothecids to hyolithids.
一种小型石鳖，具有三角形的壳盖和圆锥形的壳，尖端锋利，最初被记录为 Ambrolinevitus ventricosus，根据来自澄江生物群的新材料进行了修订。“Ambrolinevitus”ventricosus 的壳盖与来自静水沱组（寒武系 2 统）的 Paramicrocornus 的壳盖具有很强的形态相似性，表明该物种应重新分配给 Paramicrocornus。
基于 Paramicrocornus 的不寻常形态，我们在此提出了一个新的科 Paramicrocornidae fam. nov.。对寒武纪和奥陶纪石鳖的分支分析清楚地将石鳖目划分为一个单系群，它是从早期寒武纪的并系Orthothecids 进化而来的，与 Paramicrocornidae 关系最密切。
系统发育分析，以及从寒武纪到奥陶纪的石鳖分布，揭示了石鳖骨骼和软体解剖结构的假定进化模型。Paramicrocornidae 科在石鳖的进化中起着中间作用，代表了从 Orthothecids 到 Hyolithids 的进化过渡阶段。
