The late occurrence of specialized hunter-gatherer occupation of tropical rainforests in Pang Mapha, northwestern Thailand

Two archaeological sites, Tham Lod and Ban Rai rockshelters, in highland Pang Mapha, Mae Hong Son Province in northwestern Thailand have yielded several late Pleistocene to Holocene human and animal remains associated with the Hoabinhian technocomplex. Previously, stable carbon isotope compositions of human and faunal tooth enamel samples from Tham Lod Rockshelter have suggested a forest-grassland mosaic as being a Hoabinhian-related habitat in the region during the late Pleistocene. Although zooarchaeological data have implied rainforest specialization for early to mid-Holocene Hoabinhian hunter-gatherers, the extent and degree of human reliance on rainforest resources in the region have not yet been investigated in detail. To refine the timing of dietary changes and ecological adaptations of Hoabinhian hunter-gatherers in the region, we measured stable carbon isotope compositions of tooth enamel of humans and associated mammals from the early Holocene of Ban Rai Rockshelter and from several other Iron Age log-coffin sites in highland Pang Mapha, dated between 10,000 and 650 cal yr BP, in comparison with previously analyzed isotope data from the nearby late Pleistocene site of Tham Lod Rockshelter. The isotopic results from Ban Rai Rockshelter have revealed that the huntergatherers had a dietary shift to more exclusive C3 food items starting at around the early Holocene or probably during the Pleistocene-Holocene transition, despite the availability of open canopies and no clear evidence of lithic technological changes. Since that time, a succeeding human subsistence strategy with more emphasized rainforest occupation, in response to more homogeneous and closed environments and wetter climate, has possibly remained unalterable in the region. This study documents the late emergence of specialized rainforest hunter-gatherers in the highland of northwestern Thailand, compared to archaeological findings in neighboring regions. Our findings highlight the asynchronous initialization of an ecological adaptation among huntergatherers as a reaction to environmental changes across different geographical regions during the late Pleistocene and Holocene.