Diagram showing the generic (diversity) and specimen (abundance) percentages of various major groups of late Hirnantian and early Rhuddanian brachiopods (theCathaysiorthis fauna), and late Katian brachiopods in the Jiangnan Region, Southeast China.
Classification of extinction events and their severity is generally based on taxonomic counts. The ecological impacts of such events have been categorized and prioritized but rarely tested with empirical data. In a recent study, the ecological severity of the end Ordovician event was considered even less significant than that of the Serpukhovian, and is ranked only sixth within the eleven largest Phanerozoic crises since the beginning of the Ordovician Period.
South China offers a key opportunity to examine the ecological changes through the end Ordovician event in detail. Recently, to test the ecological change through the end Ordovician mass extinction, a study carried on by Prof. HUANG Bing, CAS Academician RONG Jiayu and Prof. ZHAN Renbin from Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences together with David A.T. Harper from Department of Earth Sciences, Durham University, UK.
The study based on the data from the Cathaysiorthis fauna which dominated by brachiopods from the uppermost Ordovician to lowermost Silurian of SE China, succeeding the cool-water Hirnantia Fauna. The fauna is abundant and has a relatively high diversity; these data were reported with the detailed systematic descriptions of the fauna. The spatial and temporal ranges of more than 6,500 identified specimens, from 10 collections derived from 6 localities were investigated by network and cluster analyses, nonmetric multidimensional scaling and a species abundance model. The ecological circumstances of the survival brachiopod fauna after the end Ordovician mass extinction were evaluated.
Other, older brachiopod faunas, Altaethyrella fauna and Foliomena fauna, characterizing the late Katian within the same area are compared in terms of diversity, population structure, benthic assemblage zones and relative abundance together with their major components to help further elucidate the ecological ‘turnover’ through the end Ordovician extinction event in South China. Depth zonations and structure of brachiopod assemblages along an onshore-offshore gradient in the late Katian were similar to those in the latest Ordovician–earliest Silurian (post–extinction fauna). The widths of ecological range are similar between before and immediately after the crisis that may suggest the limited ecological effect of the event.
Within this ecological framework, deeper-water faunas are partly replaced by new taxa; siliciclastic substrates continued to be dominated by the more ‘Ordovician’ orthides and strophomenides, shallow-water carbonate environments hosted atrypides, athyridides and pentamerides, with the more typical Ordovician brachiopod fauna continuing to dominate until the late Rhuddanian. The end Ordovician extinctions tested the resilience of the brachiopod fauna without damage to its overall ecological structure; that commenced later at the end of the Rhuddanian.
Reference: Huang Bing, Harper D A T, Rong Jiayu, Zhan Renbin. 2017. Brachiopod faunas after the end Ordovician mass extinction from South China: Testing ecological change through a major taxonomic crisis.Journal of Asian Earth Sciences, 138: 502–514.
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