The Pleistocene consisting of two major climatic conditions: the glacial and the interglacial, is characterized by the series of ice ages that occurred during its reign . Differences in environments and climate between these two events turn a landscape into an optimal habitat for specific land mammals, allowing only a survival of some wildlife species. By the way, the climate change affects ecosystems in a variety of ways. Unlike Europe and North America, Southeast Asia is possibly less affected by the vegetational variability because the land is traditionally supposed to have not been covered by ice. However, the impacts of climate and vegetation changes on the mammalian community during the Pleistocene are poorly known in this region.
Since the last century, the biochronologic ordering by advanced radiometric datings has become available in some Pleistocene fossil sites across Southeast Asia. The Pleistocene mammalian assemblages consist of extinct and extant tropical forested taxa recognized as “Ailuropoda-Stegodon” faunal association that covers a long range of intervals (starting from Early to Late Pleistocene). Thailand constitutes one of the significant regions in this field. The stratified fluviatile terrace of Khok Sung, Nakhon Ratchasima province, has yielded a very rich Pleistocene vertebrate fauna of Thailand, where abundant fossil mammals and reptiles (skulls, isolated teeth, and postcranial remains) were recovered. The Khok Sung fauna (dated as either 188 or 213 ka based on the paleomagnetic data and on the faunal comparisons) in northeastern Thailand comprises a diverse mammalian assemblage (at least 15 recognized species in 13 genera), relatively similar in composition to most of Pleistocene fossil sites in Southeast Asia. The chronological evidence and stable carbon isotope analysis of large mammal faunas suggest that C4 grasslands still existed and were inhabited by spotted hyaenas, Indian rhinoceroses, and several large bovid species through the Pleistocene glacialinterglacial stages, supporting the patterns of a long-term faunal stability across mainland Southeast Asia.
Although the faunal stability during the glacial-interglacial cycles makes the biochronological context of “Ailuropoda-Stegodon” association difficult to be subdivided, changes in species composition are still debated (e.g., the disappearance of Gigantopithecus and Stegodon). As temperatures decrease during the glacial stages, the habitat ranges of many Southeast Asian species have moved southward and shifted to lower elevations where temperatures are more conducive to their survival. These are cases for some caprine species (living today at the top of a mountain) that foraged in lowland grasslands and for the vegetation zones that dropped about 1,000 meters of elevation during the Pleistocene. However, the movements into less hospitable habitat, increased competition, and/or range reduction lead to global and local extinctions for some species. Future investigations into more precise chronological constraints on the fossil sites and further studies on the species diversity and ecological interactions of Pleistocene mammal faunas may hold a clue to testing for the prevalence of faunal stability and to understanding of the cause of species extinction through time across mainland Southeast Asia.