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.在阿根廷中西部内乌肯盆地（Neuquén Basin）的下白垩统阿格里奥组（Agrio Formation）中，褶蚌属（Ptychomya Agassiz）的形态变异度极高，百余年来一直困扰着传统分类学家。本研究采用此前已确立的定量研究方案，以阿格里奥组从底至顶产出的所有标本为研究材料，对该属的分类学问题进行系统厘定。双壳壳的轮廓与肋纹样式是壳体最显著的两项外部特征，本研究分别通过闭合壳轮廓与开放壳轮廓的几何形态测量法对其进行量化分析。采用基于模型的聚类法识别形态类群，并通过统计学方法检验类群间是否存在显著的形态分化鸿沟。研究结果显示，以往被归为单一物种“柯氏褶蚌（Ptychomya koeneni Behrendsen）”的形态变异，实际上对应至少4个物种的种内与种间变异；其中1个为此前未被正式描述的新种（Ptychomya esbelta sp. nov.），另有1个曾被视为柯氏褶蚌的亚种，即温氏褶蚌（Ptychomya windhauseni Weaver）。本研究同时确认了科伊科伊褶蚌（Ptychomya coihuicoensis Weaver）的物种层级地位，并证实阿格里奥组上豪特里维阶（Hauterivian）产出柯氏褶蚌。本研究相较以往对阿根廷安第斯山脉地区褶蚌属的认知水平有显著提升，增强了该属的生物地层学应用价值与古生物地理学意义，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研究提供参考范式。