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，同时也是协调停滞（coordinated stasis）概念的参考层序。本次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（Hamilton Group）与最下部的杰尼西群（Genesee Group），对其内的动物群与环境变化展开分析。此前学界已通过这套地层中识别出的显著多样性丧失、动物群迁移及生态重构，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，还是全球塔格尼克生物危机（Taghanic Biocrisis）的典型研究区域。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，从中识别出对应近岸-离岸（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出人意料的高分类学相似性，这与硅质碎屑主导的近岸环境在塔格尼克生物危机期间的持续存在密切相关；而环境梯度的离岸区域则普遍发育缺氧/贫氧环境。欧文提出的“近岸避难所模型（Nearshore Refugium Model）”，可为近岸环境中分类群在生物危机期间的存续提供合理解释。这一分类群的收缩之后，伴随残留类群以相对相似的组合形式向离岸环境扩张——阿卡迪亚造山活动增强及其引发的三角洲进积，通过缩减深水缺氧区域的范围，扩大了离岸的可栖息空间。尽管汉密尔顿与杰尼西动物群间的分类学相似性较高，但生物相结构的差异主要源于构造活动驱动的盆地物理改造及伴随的生物更替。不过，汉密尔顿近岸分类群的高分类群滞留率，加之杰尼西动物群中新增类群相对较少，使得整体分类群滞留率远高于协调停滞初始理论的观测结果。