Data from: New perspectives on transitions between ecological-evolutionary subunits in the "type interval" for Coordinated Stasis

Northern Appalachian Basin deposits and associated fossils have served as exemplars for ecological-evolutionary investigations, and as the reference interval for the concept of coordinated stasis. Here, we examine faunal and environmental changes within the uppermost Hamilton and lowermost Genesee Groups of the late Middle Devonian succession of New York State. Dramatic diversity loss, faunal migrations, and ecological restructuring recognized in these strata have been used previously to define the end of the Hamilton ecological-evolutionary subunit, and, furthermore, these strata and corresponding faunal changes represent the type region for the global Taghanic Biocrisis. We present and analyze a new, high-resolution data set of post-Taghanic Genesee fossil assemblages, in which we recognize 11 biofacies corresponding to an onshore-offshore (depth) gradient. The Genesee Fauna shows an unexpectedly high taxonomic similarity to nearshore biofacies of the pre-Taghanic Hamilton Fauna, related to the persistence of siliciclastic-dominated nearshore settings through the Taghanic Biocrisis, whereas the onset of anoxic/dysoxic conditions typified offshore portions of the environmental gradient. The “Nearshore Refugium Model” of Erwin offers a possible explanation for the persistence of taxa through the biocrisis in nearshore settings. This constriction was followed by subsequent expansion of these residual taxa to offshore environments in relatively similar associations, as increased Acadian orogenic activity and resultant delta progradation increased habitable space offshore by decreasing the extent of deeper-water, oxygen-poor settings. Although taxonomic similarity was high between the Hamilton and Genesee Faunas, biofacies structure differed primarily because of tectonically driven physical transformations to the basin and associated biotic turnover. Nevertheless, the combination of high taxonomic persistence of Hamilton nearshore taxa and the introduction of relatively few new taxa in the Genesee Fauna resulted in a taxonomic holdover that was much higher than observed in the original formulation of coordinated stasis.

北阿巴拉契亚盆地（Northern Appalachian Basin）的沉积序列及其伴生化石，长期作为生态-演化研究的经典范例，同时也是协调停滞（coordinated stasis）概念的参考层段。本研究聚焦纽约州中泥盆世晚期地层序列中最上部的汉密尔顿群与最下部的杰尼西群，对其内的动物群与环境变化展开系统性分析；此前学界已依据该套地层中识别出的显著多样性丧失、动物群迁移及生态重组现象，界定了汉密尔顿生态-演化亚单元的终结，此外这套地层及其对应的动物群变化，还是全球塔格尼克生物危机（Taghanic Biocrisis）的模式地区。我们构建并分析了一套全新的塔格尼克事件后杰尼西化石组合高分辨率数据集，从中识别出对应近岸-远岸（深度）梯度的11种生物相（biofacies）。杰尼西动物群与塔格尼克事件前的汉密尔顿动物群近岸生物相具有意料之外的高分类学相似性，这与硅质碎屑主导的近岸沉积环境在塔格尼克生物危机期间的持续存在密切相关，而环境梯度的远岸区域则以缺氧（anoxic）/次氧化（dysoxic）环境为典型特征。欧文（Erwin）提出的“近岸避难所模型”，可为近岸环境中类群在生物危机期间的存续现象提供合理解释。此类类群存续的收缩过程之后，伴随阿卡迪亚造山运动（Acadian orogenic activity）增强及由此引发的三角洲进积，深水缺氧环境的分布范围大幅缩小，远岸可栖息空间得以扩张，这些残存类群以相对相似的组合形式逐步向远岸环境扩张。尽管汉密尔顿与杰尼西动物群的分类学相似性较高，但二者的生物相结构差异显著，这主要源于盆地受构造驱动的物理改造及伴随的生物更替。不过，汉密尔顿近岸类群的高分类学存续性，加上杰尼西动物群中新增类群相对较少，共同造就了远高于协调停滞初始表述中所观测到的类群留存率。