Data from: Proteroctopus ribeti in coleoid evolution

Palaeontological data are key elements for inferring ancestral character states and the assembly of character complexes, but cephalopod fossils preserving soft tissues are very rare. The exceptionally well-preserved, unique specimen of Jurassic Proteroctopus ribeti Fischer & Riou from the Lagerstätte of La-Voulte-sur-Rhône (c. 165 Ma, France) is one of the few fossil octopod related taxa, but is rarely considered in evolutionary studies. In this paper, we used synchrotron microtomography to reappraise its external characters and for the first time, to reveal its internal structures. A unique character association is found with two fins, head fused to the body, eight well-developed arms with cirri and two rows of oblique suckers, a gladius and absence of an ink sac. The phylogenetic analysis indicates that Proteroctopus is a basal member of the Vampyropoda. However, this result should be interpreted with caution due to the number of unknown character states in the matrix. Contrary to previous assumptions, the phylogenetic position of Proteroctopus, as well as its stratigraphic occurrence, suggest that the arrangement of biserial suckers may be the ancestral condition in Vampyropoda.

古生物学数据是推断祖先性状状态与性状复合体组装的核心要素，但保存软组织的头足类（cephalopod）化石极为稀缺。产自法国罗讷河畔拉武尔特特异埋藏化石库（Lagerstätte，约1.65亿年）的侏罗纪鲁氏原章鱼（Proteroctopus ribeti Fischer & Riou）标本，保存状态极佳且独一无二，是少数与章鱼类相关的化石类群之一，却极少在进化研究中被纳入考量。本研究借助同步辐射显微断层扫描（synchrotron microtomography）技术，重新评估了该标本的外部性状，并首次揭示了其内部结构。研究发现其具备独特的性状组合：具两片鳍，头部与躯体愈合，8条发育完好且带有腕突的腕足，两排倾斜排布的吸盘，存在角质内壳（gladius）且无墨囊（ink sac）。系统发育分析（phylogenetic analysis）结果显示，原章鱼属（Proteroctopus）为蛸形总目（Vampyropoda）的基干类群。但由于分析矩阵中存在大量未知性状状态，该结论需谨慎解读。与既往假设相悖的是，原章鱼属的系统发育位置及其地层产出背景表明，双排吸盘的排布模式可能是蛸形总目的祖先性状状态。