Unionidae (Bivalvia; Palaeoheterodonta) from the Palaeogene of northern Vietnam: exploring the origins of the modern East Asian freshwater bivalve fauna

Abstract

Eocene/Oligocene sediments deposited in two Cenozoic pull-apart basins in northern Vietnam, i.e. the Na Duong and Cao Bang basins, yield several rich and well-preserved assemblages of unionid bivalves. This study outlines the taxonomy of the Unionidae from these communities, and all taxa are described and illustrated in detail. As far as we are aware, this is the first comprehensive treatment of Cenozoic Unionidae from South-East Asia. Eight of the nine taxa are described as new to science. Four species – Cuneopsis quangi sp. nov., Cristaria mothanica sp. nov., Cristaria falcatocostata sp. nov. and Lamprotula hungi sp. nov. – can be confidently assigned to modern genera. The generic position of the remaining species is equivocal (?Nodularia cunhatia sp. nov., ?Cuneopsis sp., ?Lanceolaria sp., ?Lamprotula sp.) or remains tentative (Anodontini sp.). The phyletic relationships of the fossil taxa to modern species are discussed and interpreted in light of the Cenozoic tectonic history of South-East Asia and the intimately associated evolution of drainage systems. The results confirm a close relationship of the fossil unionids to the modern mussel fauna of the Yangtze, Pearl and Red River catchment areas. Moreover, the fossils from Cao Bang and Na Duong are among the earliest confirmed records of all genera identified, and thus document an important, early stage in the development of the modern East and South-East Asian bivalve faunas.

http://zoobank.org/urn:lsid:zoobank.org:pub:D52F10F0-1AFF-4EFD-B724-692E982143E4

Keywords:

• freshwater mussels
• East Asia
• Eocene–Oligocene
• Red River
• Yangtze

Acknowledgements

We owe thanks to the following people and organizations that enabled us to carry out this study: Đng Ngc Trân (Department of Geology and Minerals of Vietnam, Hanoi) arranged the international cooperation and organized permits for fieldwork and sampling; Nguyn Viˆt Hung and Đ Dúc Quang (both Geology Museum, Hanoi) greatly helped with local organization and assisted in the field; Ulrich Projahn and Stefan Sónyi (both Bayerische Staatssammlung für Paläontologie und Geologie, Munich) carried out the mechanical preparation of the fossils and production of casts; Phillipe Bouchet and Virginie Héros (both Museum National d’Histoire Naturelle, Paris) and Ronald Janssen (Senckenberg Naturhistorische Sammlungen, Frankfurt/Main) kindly granted access to the collections under their care; Ronald Janssen and Daniel L. Graf (University of Alabama, Tuscaloosa) gave valuable comments on taxonomy; Mathias Harzhauser (Naturhistorisches Museum Wien) and Larisa Prozorova (Institute of Biology and Soil Sciences, Vladivostok) provided literature; Michael Krings (Bayerische Staatssammlung für Paläontologie und Geologie, Munich) polished the English. The manuscript also benefitted from the constructive comments of two anonymous reviewers. Fieldwork in Vietnam was financed by the Deutsche Forschungsgemeinschaft (DFG; grant number BO 1550/11–1), and the visit of S.S. to the MNHN Paris was financed by SYNTHESYS (grant number FR-TAF-801).