47 THE RAFFLES BULLETIN OF ZOOLOGY 2011 EVIDENCE OF THE EARLIEST FRESHWATER DECAPOD FOSSIL FROM SOUTHEAST ASIA (CRUSTACEA: DECAPODA: BRACHYURA) Sebastian Klaus Goethe-Universität, Department of Ecology and Evolution, Siesmayerstrasse 70A, 60054 Frankfurt am Main, Germany Department of Biological Science, National University of Singapore, 14 Science Drive 4, Singapore 117543, Republic of Singapore Email: klaus@bio.uni-frankfurt.de Madelaine Böhme Senckenberg Center for Human Evolution and Palaeoecology (HEP), Eberhard-Karls-Universität Tübingen, Institute for Geoscience, Sigwartstrasse 10, 72076 Tübingen, Germany Email: m.boehme@ifg.uni-tuebingen.de Simon Schneider Bayerische Staatssammlung für Paläontologie und Geologie, Richard-Wagner-Strasse 10, 80333 München, Germany Email: s.schneider@lrz.uni-muenchen.de Jérôme Prieto Senckenberg Center for Human Evolution and Palaeoecology (HEP), Eberhard-Karls-Universität Tübingen, Institute for Geoscience, Sigwartstrasse 10, 72076 Tübingen, Germany Ludwig-Maximilians-Universität München, Department of Earth and Environmental Sciences, Palaeontology and Geobiology, Richard-Wagner-Strasse 10, 80333 München, Germany Email: j.prieto@lrz.uni-muenchen.de Boungnavong Phetsomphou Viangphoukha Coal Mine Co. LTD, Lao PDR Email: VPKS3@hotmail.com ABSTRACT. – We report the first evidence for Miocene brachyuran freshwater crabs from Southeast Asia, a hotspot of extant freshwater crab biodiversity. This confirms the presence of potamoid freshwater crabs in Southeast Asia during the Miocene, as suggested by previous molecular clock estimates. The specimen (one claw fragment) originates from the Middle to Late Miocene site of Vieng Phouka, Lao People’s Democratic Republic. Sedimentological and palaeontological data indicate the former existence of alternating swampy and lacustrine environments, inhabited by the crab and a low-diversity gastropod fauna. KEYWORDS. – Miocene, Laos, Vieng Phouka, Potamidae, Gecarcinucidae. THE RAFFLES BULLETIN OF ZOOLOGY 2011 59(1): 47–51 Date of Publication: 28 Feb.2011 © National University of Singapore INTRODUCTION The fossil record of freshwater decapod crustaceans is generally very sparse (Glaessner, 1969; Rode & Babcock, 2003; Klaus & Gross, 2010), especially in tropical Asia. In contrast, Southeast Asia represents a biodiversity hotspot for extant primary freshwater brachyurans (Yeo et al., 2008; Cumberlidge et al., 2009; Klaus et al., 2009). Primary freshwater crabs can be considered as those brachyuran families that lack any marine members (see Yeo et al., 2008), and occur in Southeast Asia as the families Potamidae and Gecarcinucidae, together comprising about 12% of the total number of currently described brachyuran species (Ng et al., 2008; Yeo et al., 2008; Cumberlidge et al., 2009). However, the fossil record of these families is restricted to the geographic periphery regarding current regions of species richness. For example, Potamon sivalense was described by Glaessner (1933) from the Siwalik beds (Middle Miocene to Pliocene) in the northern part of the