As a main component of the Palaeozoic Evolutionary Fauna (Sepkoski 1981, 1984; Sheehan 1982), brachiopods were major contributors to the Ordovician biodiversification event (Webby 2000; Webby et al. 2004). Orthides, strophomenides, and pentamerides (syntrophidines) were important brachiopod groups that went through three pulses of radiation during the Ordovician (Harper et al. 2004), with the origin and proliferation of strophomenide post-dating those of pentamerides and orthides. Within the Order Strophomenida, the oldest reported plectambonitoid, AkelinaSevergina, 1967, came from the late Tremadoc Algan Formation of Gorny Altai, Russia, although the taxonomic position of this genus remains questionable (e.g. Cocks and Rong 1989, 2000). The undisputed first appearance of plectambonitoids is PlectellaLamansky, 1905 from lower Arenig strata in the Tallinn area of Estonia (Öpik 1933; Cocks and Rong 2000).
Pioneer taxa of the strophomenoids have been reported from Mid Ordovician strata in several palaeocontinents, such as Laurentia (Salmon 1942; Cooper 1956), Baltica (Neuman and Bruton 1974), Avalonia (Lockley and Williams 1981), and South China (Rong et al. 1999). The oldest known so far is from South China (Zhan and Rong 2003, 2006; Zhan et al. 2004) where plectambonitoids and strophomenoids first appeared in the Acrograptus filiformis Biozone (earliest Arenig, early Floian) and the Expansograptus hirundo Biozone (early late Arenig, early Mid Ordovician) respectively, and reached their first diversity acme during the Llanvirn (Darriwilian). Thus, the first diversification of strophomenides in South China predated that in most other regions of the world by 2–3 graptolitic biozones (see Harper et al. 2004).
Globally, the last radiation of strophomenide brachiopods in the Ordovician occurred during the mid Ashgill. Among the best examples of this event are the Richmondian brachiopod fauna of Laurentia (e.g. Howe 1965, 1988; Dewing 1999) and the unusually rich and diverse strophomenides of the Boda Limestone of Sweden (Cocks 2005). In South China, rich and diverse brachiopod faunas of mid Ashgill age are known only in western Zhejiang and north-eastern Jiangxi provinces, with a number of localities yielding abundant strophomenides, as well as orthides (Zhan and Rong 1994, 1995a; Zhan and Cocks 1998).
At the Jianglütang section in Chun’an County, western Zhejiang Province, strophomenide brachiopods are unusually rich and diverse at some levels in the upper Changwu Formation. During the 2003 field season, a rich suite of brachiopods was collected from a fossiliferous horizon in the upper part of the formation, which also yielded trilobites, bivalves, ostracods, and bryzoans. In taxonomic composition, the brachiopod fauna of the Changwu Formation is similar to that from the coeval mid Ashgill rocks in the border region of Zhejiang and Jiangxi provinces (Zhan and Cocks 1998), but the abundance of strophomenide brachiopods is a distinct character of the Changwu fauna in the Chun’an area. In this respect, the strophomenides from the Changwu Formation of western Zhejiang hold important information on mid Ashgill brachiopod radiation in South China. The main objectives of this paper are to provide a systematic description of this group of brachiopods and to analyse their faunal affinities with coeval faunas in other palaeogeographical regions.