Disponible en ligne sur www.sciencedirect.com Annales de Paléontologie 97 (2011) 113–131 Original article Neogene reptiles of northeastern Thailand and their paleogeographical significance Les reptiles néogènes du nord-est de la Thaïlande et leur intérêt paléogéographique a,∗ b,c d,e Julien Claude , Wilailuck Naksri , Nareerat Boonchai , f d c Eric Buffetaut , Jaroon Duangkrayom , Chalida Laojumpon , d b,c b Pratueng Jintasakul , Komsorn Lauprasert , Jeremy Martin , b g Varavudh Suteethorn , Haiyan Tong a UM2, CNRS, IRD, université de Montpellier 2, institut des sciences de l’évolution de Montpellier, 2, place Eugène-Bataillon, cc064, 34095 Montpellier cedex 5, France b Palaeontological Research and Education Center, Mahasarakham University, Khamriang, Kantharawichai, 44150 Mahasarakham, Thailand c Department of Biology, Faculty of Science, Mahasarakham University, Khamriang, Kantarawichai, 44150 Mahasarakham, Thailand d Northeastern Research Institute of Petrified Wood and Mineral Resources, Nakhon Ratchasima, Thailand e Research Center of Paleontology and Stratigraphy, Jilin University, Changchun, 130026 Jilin, China f Laboratoire de géologie de l’école normale supérieure, UMR 8538CNRS, 24, rue Lhomond, 75231 Paris cedex 05, France g 30, rue Carnot, 94270 Le Kremlin-Bicêtre, France Available online 24 October 2011 Abstract In the last ten years, several fossil localities in Nakhon Ratchasima Province (northeastern Thailand) have yielded late Neogene turtle and crocodile taxa. Although not always well dated, the age of all these fossils is constrained between Middle Miocene and Pleistocene. Several crocodile taxa have been discovered: Crocodylidae, Alligatoridae and Gavialidae. In particular, the presence of Gavialis is attested in northeastern Thailand during the Pleistocene. Fossil turtles belong to several families: Geoemydidae, Testudinidae, and Trionychidae. In addition to the discovery of giant continental tortoises, some large aquatic trionychid and geoemydid turtles are present. The latter are only found in larger river systems and no longer encountered in the Mun or Chi Rivers of northeastern Thailand. Most fossil forms correspond to modern species and reveal interesting changes in biogeographical distribution patterns. These changes are likely related to changes in ∗ Corresponding author. E-mail address: [email protected] (J. Claude). 0753-3969/$ – see front matter © 2011 Elsevier Masson SAS. All rights reserved. doi:10.1016/j.annpal.2011.08.002 114 J. Claude et al. / Annales de Paléontologie 97 (2011) 113–131 the size of the drainage and direction of the Mun River system. We suggest that the Mun River was probably not flowing from west to east to the Mekong River system as today but that it was flowing from east to west to the Chao Phraya River system. © 2011 Elsevier Masson SAS. All rights reserved. Keywords: Crocodiles; Turtles; Southeast Asia; Cenozoic; Paleohydrogeography Résumé Plusieurs localités fossilifères ont livré des restes de vertébrés néogènes dans la province de Nakhon Ratchasima ces dernières années. Ces sites, souvent mal datés, sont calés stratigraphiquement entre le Miocène moyen et le Pléistocène. Parmi les vertébrés mis au jour, on note la présence d’une faune intéressante de tortues et de crocodiles, comportant en particulier des gavialidés, des crocodilidés et des alligatoridés. La faune de tortues est représentée par les familles des géoémydidés, des testudinidés (avec en particulier des tortues géantes) et des trionychidés. La plupart des formes aquatiques retrouvées sont caractéristiques de grands cours d’eaux, et ne sont pas retrouvées aujourd’hui dans les rivières Mun et Chi qui sont les deux majeurs cours d’eau du Nord-est de la Thaïlande. Ces fossiles comparables aux formes actuelles suggèrent des modifications importantes des systèmes fluviaux de la région. La biogéographie de ces faunes soutient l’hypothèse que la rivière Mun coulait d’Est en Ouest vers la Chao Phraya. © 2011 Elsevier Masson SAS. Tous droits réservés. Mots clés : Crocodiles ; Tortues ; Asie du Sud-est ; Cénozoïque ; Paléohydrogéographie 1. Introduction 1.1. General context Specific studies of Neogene reptiles from mainland Southeast Asia are extremely rare in the literature. The first mention is probably “Geoclemys palaeannamitica” from a Neolithic site of Vietnam (Bourret, 1941). This species was later referred to the genus “Chinemys” by Bour in 1980 (Bour, 1980). Although fossil remains of freshwater reptiles are not rare in the Cenozoic of mainland Southeast Asia, few of them were described in detail from the Paleogene (in Thailand, Claude et al., 2007; Martin and Lauprasert, 2010; in Myanmar, Hutchison et al., 2004), and even less have been described or mentioned from the Neogene (most records are from Thailand, see Tong et al., 2006 for an overview). Although little has been published about freshwater vertebrates; they can, however, contribute to test hypotheses concerning the complex hydrogeographic history of the area (Gregory, 1925; Hutchison, 1989). Indeed, most hypotheses regarding paleohydro- geography are inferred from geomorphological data and confronted to the distribution of living species and variation of molecular data (e.g. Attwood and Johnston, 2001; Meijaard and Groves, 2006), but rarely related to past organisms distribution known from fossils. In Thailand, turtles and crocodiles are known from Miocene localities in the north and in the northeastern parts of the country, but have not been studied in detail. Middle Miocene localities of northern Thailand have yielded freshwater geoemydids, trionychids, and testudinid tortoises, and alligatorids, which have been found in lacustrine environments. These faunas will be described in detail in a future study. By contrast to northern Thai localities, the geological context of northeastern Thailand is younger and clearly fluvial. This context can be very informative for understanding the late evolution of the hydrogeographic system in Southeast Asia via the use of freshwater fossil organisms. The J. Claude et al. / Annales de Paléontologie 97 (2011) 113–131 115 purposes of this paper are to provide preliminary specimen descriptions and taxonomic lists for the northeastern localities in terms of reptile diversity and to discuss the hydrogeographic history of the Mun River, within the framework of hypotheses regarding its relationships with the Mekong and other river systems. 1.2. Abbreviations and collections All fossils described in this paper are kept in the collections of the Northeastern Research Institute of Petrified Wood and Mineral Resources, Nakhon Ratchasima, Thailand (RIN); and in the collections of the Department of Mineral Resources (DMR) in Bangkok, Khok Sung village (Nakhon Ratchasima Province), and Sirindhorn Museum, Sahat Sakhan (Kalasin Province). 1.3. Geographical context The three localities having yielded Neogene reptiles in northeastern Thailand are located in Nakhon Ratchasima Province (Figs. 1 and 2), close to the Mun River. Today, the Mun originates in the Sankamphaeng range (or Sankambeng range) in Khao Yai National Park and flows northwards and then eastwards to join the Mekong River in Khong Chiam city in Ubon Rachatani Province (Fig. 1). The main tributary of the Mun is the Chi River (the longest Thai river), which runs north of the Mun River but carries less water. 1.4. Geological context Fossils were usually found when digging reservoirs or during gravel and sand extraction, these activities being commonly undertaken in Neogene sediments in Nakhon Ratchasima Province (in contrast to the lower part of the Mun River). Neogene sediments in this region consist of layers of sand, conglomerate, or mud and were clearly deposited in a fluvial context. These sediments were accumulated and preserved around the present Mun River and overlie Cretaceous formations (Khok Kruat or Mahasarakham Formation in this area). Outcrops or pits are often temporary, superficial and pits become rapidly flooded. Moreover, lateral continuity of the sedimentary bodies is usually not well developed, precluding litho stratigraphic correlations between the various pits. It is also likely that a lot of material has been reworked in this sedimentological context. According to the amount of Neogene sediments, and the nature of conglomerates, it is not clear whether these sediments were deposited by the present-day Mun River (see the discussion). According to the mammal assemblages, the Neogene sediments around Nakhon Ratchasima are thought to have been deposited from the Middle or Late Miocene to the Pleistocene (Department of Mineral Resources, 2005; Hanta et al., 2008). 2. Tha Chang Area Fossils have been found in the area of Tha Chang in Chaloem Pra Kiat district during excavation and mining in sand pits (Fig. 1) (Plate 1). In this area, the current day Mun River flows very close to the fossil beds (pits are dug on both sides of the river). Eight sand pits at least are said to have yielded fossil vertebrates in this area, especially elephant teeth (Hanta et al., 2008). The fossils are usually recovered during the extraction of sand from the walls of the pits with a high-pressure water jet. In this context, most of the fossils are collected by local villagers working in the sand pits. Few fossils are brought by villagers and kept in institutions 116 J. Claude et al. / Annales de Paléontologie 97 (2011) 113–131 Fig. 1. Hydrogeographical and geographic context. Contexte géographique et hydrogéographique. J. Claude et al. / Annales de Paléontologie 97 (2011)