A complete skull of Crocuta crocuta ultima indicates a late Middle Pleistocene age for the Khok Sung (northeastern Thailand) vertebrate fauna

The locality of Khok Sung, Nakhon Ratchasima province, which corresponds to an ancient river terrace, has yielded the richest Pleistocene fauna of Thailand with a thousand of fossil vertebrate remains. This fauna has been previously dated between the Early Pleistocene and the Middle Pleistocene. We describe here a nearly complete hyaenid skull and associated mandible identified as belonging to spotted hyaena Crocuta crocuta ultima. The spotted hyaena C. c. ultima, which extended its maximum latitudinal distribution from northern China to Peninsular Thailand, is a characteristic component of Southeast Asian Middle Pleistocene faunas. These new biochronological data, coupled with a magnetostratigraphic study of the lithological section, provide a powerful multiproxy approach for the dating of Khok Sung fauna, pinpointing rather a late Middle Pleistocene age than the Early Pleistocene. In addition, the occurrence in the Khok Sung section of a short reverse excursion of the magnetic field within the Brunhes normal Chron can be tentatively identified as corresponding either to the “Iceland Basin” (188 ka) or to the “Pringle Falls” (213 ka) excursion, suggesting an even more precise dating of the locality. According to the presence of a spotted hyaena, the Khok Sung fauna may illustrate an open canopy habitat in a floodplain with abundant and diversified herbivores, close to the main river channel. This interpretation contrasts with the paleobotanical data which indicate wet and dry tropical forests and may instead describe the surrounding upland vegetation.