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.

阿巴拉契亚盆地北部（Northern Appalachian Basin）的沉积序列及其伴生化石，长期以来作为生态-演化研究的典型范例，同时也是协同停滞（coordinated stasis）概念的参考层位。本研究聚焦纽约州晚中泥盆世地层序列中最顶部的汉密尔顿群（Hamilton Group）与最底部的杰尼西群（Genesee Group）内部的动物群与环境变化。此前学界依据该地层中识别出的剧烈多样性丧失、动物群迁移及生态系统重构，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，也是全球塔格尼克生物危机（Taghanic Biocrisis）的标准研究区域。本研究构建并分析了一套全新的塔格尼克事件后杰尼西群化石组合高分辨率数据集，从中识别出11个对应近岸-远岸（水深）梯度的生物相（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展现出意料之外的高分类学相似性，这与以陆源碎屑岩为主的近岸沉积环境在塔格尼克生物危机期间得以持续存在密切相关；而环境梯度的远岸区段则以缺氧/贫氧（anoxic/dysoxic）环境的出现为典型特征。欧文的“近岸避难所模型”（Nearshore Refugium Model）为分类群在生物危机期间于近岸环境中得以存续提供了可行解释。在这一类群收缩之后，随着阿卡迪亚造山作用（Acadian orogenic activity）增强及其引发的三角洲进积，深水缺氧环境的范围被缩小，远岸可栖息空间得以扩张，这些残存类群便以相对相似的组合形式向远岸环境扩散。尽管汉密尔顿动物群与杰尼西动物群的分类学相似性较高，但两者的生物相结构差异显著，这主要源于构造活动驱动的盆地物理改造及与之相关的生物更替。尽管如此，汉密尔顿动物群近岸类群的高分类群存续率，加之杰尼西动物群中新引入类群数量相对较少，共同造就了远高于协同停滞原始定义中所观测到的分类群留存比例。