A new Miocene and Pleistocene continental locality from Nakhon Ratchasima in Northeastern Thailand and its importance for vertebrate biogeography

Two new fossil assemblages are described from Sin Charoen sandpit exploited in Phimai District, Nakhon Ratchasima Province, Northeastern Thailand. In this province, vertebrate fossils have been yielded from the Miocene to the Pleistocene deposits. The Miocene fauna has been documented in detail by a rich fossil record from several localities in Chaloem Phra Kiat District, while the Pleistocene fauna has been well studied in Khok Sung sandpit in Mueang Nakhon Ratchasima District. The fossil assemblage from the upper section of Sin Charoen sandpit is similar to the Middle Pleistocene fauna of Khok Sung, which is composed of extinct and extant species of mammals and reptiles. Moreover, the finding of Gavialis cf. bengawanicus and Duboisia santeng demonstrates a strong faunal relationship with Early-Middle Pleistocene faunas of Java (e.g., Trinil). The occurrence of large fluviatile turtles and gharials from Sin Charoen sandpit indicates that the past river system was more developed than today and that the Khorat Plateau was at a lower elevation at the time of deposition. The fossil assemblage from the lower section includes two rhinocerotids and an advanced form of the genus Stegolophodon and is similar to the Late Miocene fauna found in situ in the sandpits of Chaloem Phra Kiat District.