Data from: Taxonomy of the bivalve Ptychomya in the Lower Cretaceous of the Neuquén basin (west-central Argentina)

In the Lower Cretaceous Agrio Formation, Neuquén Basin (west-central Argentina), the highly variable genus Ptychomya Agassiz has challenged traditional taxonomists for over a century. Here we apply a previously outlined quantitative protocol in order to settle the taxonomy of the genus based on specimens recorded from the base to the top of the Agrio Formation. The shell outline and ribbing pattern, two prominent external features of the valves, were quantified using geometric morphometric measurements of closed and open outlines, respectively. Morphological groupings were identified using model-based clustering, and the presence of significant morphological gaps between them was statistically tested. Our results show that the variation historically attributed to a single species, namely Ptychomya koeneni Behrendsen, corresponds to intra- and interspecific variability of at least four species, one of which was previously unknown (Ptychomya esbelta sp. nov.) whereas another was regarded as a subspecies of P. koeneni, namely Ptychomya windhauseni Weaver. We were also able to confirm the specific rank of Ptychomya coihuicoensis Weaver and the presence of P. koeneni in the upper Hauterivian of the Agrio Formation. This study represents a significant improvement over the previous state of knowledge of the genus Ptychomya in the Andes of Argentina, enhancing its biostratigraphical usefulness and palaeobiogeographical significance, and may serve as a model for the study of other poorly known bivalve faunas from other Andean basins of South America.

阿根廷中西部内乌肯盆地（Neuquén Basin）下白垩统阿格里奥组（Agrio Formation）产出的褶纹蛤属（Ptychomya Agassiz）具有极高的形态变异性，一个多世纪以来始终困扰着传统分类学家。本研究基于阿格里奥组从底至顶产出的全部标本，采用此前已提出的定量化研究方案，旨在厘清该属的分类问题。双壳的壳形轮廓与肋纹样式是其两大典型外部特征，本研究分别通过闭合壳形轮廓与张开壳形轮廓的几何形态测量法（geometric morphometric measurements）对其进行量化分析。研究采用基于模型的聚类法（model-based clustering）识别形态类群，并通过统计学检验验证类群间是否存在显著的形态分异间隙。研究结果显示，以往被归为单一物种柯氏褶纹蛤（Ptychomya koeneni Behrendsen）的形态变异，实际上至少对应4个物种的种内与种间变异，其中1个为新发现物种（Ptychomya esbelta sp. nov.），另1个此前曾被视为柯氏褶纹蛤的亚种，即温氏褶纹蛤（Ptychomya windhauseni Weaver）。本研究还确认了科伊胡伊科褶纹蛤（Ptychomya coihuicoensis Weaver）的物种有效性，以及阿格里奥组上豪特里维阶（Hauterivian）中存在柯氏褶纹蛤。本研究较以往对阿根廷安第斯地区褶纹蛤属的认知水平有显著提升，增强了该属的生物地层学与古生物地理学研究价值，同时可为南美其他安第斯盆地中研究程度较低的双壳类动物群提供参考范式。