Data from: A new paleoecological look at the Dinwoody Formation (Lower Triassic, western U.S.): intrinsic versus extrinsic controls on ecosystem recovery after the end-Permian mass extinction

The Dinwoody Formation of the Western U.S. represents an important archive of Early Triassic ecosystems in the immediate aftermath of the end-Permian mass extinction. We present a systematic description and a quantitative paleoecological analysis of its benthic faunas in order to reconstruct benthic associations and to explore the temporal and spatial variations of diversity, ecological structure and taxonomic composition throughout the earliest Triassic of the western U.S. A total of 15 bivalve species, two gastropod species, and two brachiopod species are recognized in the study area. The paleoecological analysis shows that the oldest Dinwoody communities are characterized by low diversity, low ecological complexity and high dominance of few species. We suggest that this diversity-low most likely reflects the consequences of the mass extinction in the first place and not necessarily the persistence of environmental stress. Whereas this diversity pattern persists into younger strata of the Dinwoody Formation in outer shelf environments, an increase in richness, evenness and guild diversity occurred around the Griesbachian-Dienerian boundary in more shallow marine habitats. This incipient recovery towards the end of the Griesbachian is in accordance with observations from other regions and thus probably represents an interregional signal. In contrast to increasing richness within communities (alpha-diversity), beta-diversity remained low during the Griesbachian and Dienerian in the study area. This low beta-diversity reflects a wide environmental and geographical range of taxa during the earliest Triassic, indicating that the increase of within-habitat diversity has not yet led to significant competitive exclusion. We hypothesize that the well-known prevalence of generalistic taxa in post-extinction faunas is primarily an effect of reduced competition that allows species to exist through the full range of their fundamental niches, rather than being caused by unusual and uniform environmental stress.

美国西部的丁伍迪组（Dinwoody Formation）是二叠纪末大灭绝（end-Permian mass extinction）事件发生后的直接后续时段内，三叠纪最早期生态系统的重要遗存档案。本研究对该组的底栖动物群（benthic faunas）开展系统性描述与定量古生态分析，旨在重建底栖组合，并探究美国西部三叠纪最早期，多样性、生态结构及分类组成的时空变化规律。研究区域共识别出15种双壳类、2种腹足类及2种腕足类。古生态分析结果显示，最古老的丁伍迪群落以低多样性、低生态复杂度以及少数物种占据绝对优势为特征。我们认为，这种低多样性特征大概率直接反映了大灭绝事件的后续影响，而非一定源于持续存在的环境压力。在外陆棚环境的丁伍迪组较年轻地层中，该多样性模式得以延续；而在更浅的海相生境中，格里斯巴赫阶-迪内尔阶界线（Griesbachian-Dienerian boundary）附近，物种丰富度、均匀度及功能类群多样性均出现上升。格里斯巴赫阶末期的这种初始复苏现象与其他地区的观测结果一致，因此可能代表了一种跨区域的复苏信号。与群落内丰富度（即α多样性）上升形成鲜明对比的是，研究区域内格里斯巴赫阶与迪内尔阶的β多样性始终处于较低水平。这种低β多样性反映出三叠纪最早期类群拥有广泛的环境与地理分布范围，表明栖息地内多样性的提升尚未引发显著的种间竞争排斥。我们提出假说：灭绝后动物群中广为人知的广适性类群（generalistic taxa）占优现象，主要源于竞争减弱使得物种得以在其基础生态位的全部范围内存续，而非由异常均一的环境压力所导致。