Abstract The upper Daguanshan Formation (middle Expansograptus hirundo graptolite biozone, Dapingian, early Middle Ordovician) of the Shuanghe area, Changning County, southern Sichuan Province, contains three new genera and species of strophomenoids: Ochyromena plana , Shuangheella elongata , and Primotimena globula , which are attributed to the Strophomenidae, Rafinesquinidae and Glyptomenidae respectively. These are the earliest known strophomenoids from the South China palaeoplate, and also the oldest rafinesquinid and glyptomenid brachiopods worldwide. Global review of the superfamily Strophomenoidea of Middle Ordovician age suggests that the first diversity peak at the species level occurred in late Darriwilian (Llanvirn) time, mainly as a result of the rapid diversification of the family Strophomenidae. The first appearance datum (FAD) of strophomenoids and their possible westward dispersal were from North China (latest Floian) and/or South China (early Dapingian), through the Chu‐Ili terrane of Kazakhstan, Iran, and Baltica (early Darriwilian), to Avalonia and Laurentia (late Darriwilian). This points to the existence of early diversification hotspots of the strophomenoid superfamily in the North and South China palaeoplates during the early Middle Ordovician in generally shallow water (corresponding to BA2) environments. The high degree of similarity in the external morphology and ventral interior of the three new genera indicates that the early diversification of strophomenoids began with differentiation of the cardinalia, especially in the configuration of the bilobed cardinal process, a key evolutionary novelty for the strophomenoids.
AbstractA relatively diverse Saucrorthis brachiopod fauna is reported for the first time from the Sibumasu palaeoplate in the Shihtien Formation (Darriwilian, upper Middle Ordovician) at Laojianshan of Baoshan, western Yunnan Province, southwest China. It contains 25 brachiopod genera, amongst which orthides, strophomenides and billingsellides are predominant, but quantitatively Saucrorthis and Leptestiina are the most abundant. Numerical analyses of 23 global Darriwilian brachiopod faunas show two major clusters, the Saucrorthis Group and the Aporthophyla Group, representating two major palaeobiogeographical regions developed during the Darriwilian, corresponding to lower and higher palaeolatitudinal habitats, respectively.Keywords:: Saucrorthis faunaDarriwilian (Middle Ordovician)Baoshan of YunnanSibumasu palaeoplate AcknowledgementsFan Junxuan, Ma Xuan, Wang Yuan and Guo Zhengfu from the Nanjing Institute of Geology and Palaeontology (NIGP) extended their help in the field. Critical reviews by Ian Percival and Christian Rasmussen, and suggestions from journal editors, Mikael Calner and David Harper, greatly helped improve the presentation of this manuscript. Financial supports are from the Chinese Academy of Sciences (CAS), the National Nature Science Foundation of China (40825006, 41221001, 41290260) and the State Key Laboratory of Palaeobiology and Stratigraphy (LPS). This paper is a contribution to the IGCP project 591 "The Early-Middle Paleozoic Revolution".
Reexamination and serial sectioning of the type material of Reticularia septentrionalis Whiteaves 1904 and Meristina expansa Whiteaves 1904, from the Silurian (upper Llandovery) Attawapiskat Formation, Ekwan River, Hudson Bay Lowlands, indicate that they belong to the same species and that they can be assigned to the genus Pentameroides. These described species are also identical to Sapelnikovia [=Reveroides] norfordi Boucot and Johnson 1979, from the same formation on the Attawapiskat River nearby. All three species are thereby assigned to a single species, Pentameroides septentrionalis. The inflated shell of this species ranges from smooth and nonlobate to bisulcate–bilobate and rarely weakly trisulcate. This morphology is thereby viewed as a species-specific character, leading to the conclusion that Reveroides Sapelnikov 1976 is probably a junior synonym of Pentameroides.
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