During the Last Glacial Period, global climate fluctuated frequently, profoundly shaping the evolution and migratory histories of mammals. The abundant geological and biological records preserved within the Hanzhong Tiankeng Group provide invaluable resources for reconstructing past climates and environments. Tianxingyan shaft is situated in Ganhegou Village, Xiaonanhai town, Nanzheng district, Hanzhong city. It is one of the largest and most complete shafts within the Xiaonanhai Tiankeng Group. It is a spectacular 82-m-deep collapse feature, elevated at 932 meters above sea level. Tianxingyan shaft opens through limestones of the Late Permian Wujiaping Formation, which dip gently to southeast and are rhythmically bedded with layers measuring 30–40 cm, with some layers being 5–8 cm. A small rock-shelter excavated 26 m below the rim on the eastern wall yielded a fragmentary left second lower molar of Stegodon orientalis as described by Li et al. (2021). The specimen preserves only five lophids along a crown length of 80 mm, a width of 85 mm, and a height of 40 mm, resulting in a lophid frequency of 3.7. The enamel is thin (≈3 mm), strongly folded, and the valleys are densely packed with cement—morphometric features that align unambiguously with S. orientalis specimens from Panxian Dadong, Chongzuo Hejiang, and other classic Late Pleistocene cave sites in South China.

To determine the absolute age of this northernmost record, we applied two independent techniques to the same individual. U-series dating was conducted on both enamel and a thin micritic carbonate rind adhering to the fossil surface. Enamel chips (TXYF-01-A, -B) were micro-drilled, spiked with a ²²⁹Th-²³³U-²³⁶U tracer, and analyzed on a Neptune Plus MC-ICP-MS at Xi’an Jiaotong University, following the protocols of Cheng et al. (2013). The high U contents (50–60 ppm) and elevated ²³⁰Th/²³²Th_initial ratios (≈8×10⁻⁶) yielded two precise apparent ages of 24.0 ± 0.4 kyr and 14.2 ± 0.1 kyr (2σ), but diagenetic uptake of U renders these minima. A third analysis of the surface carbonate (TXYF3-2) produced 32.3±1.6 kyr (uncorrected) and 22.1±14.5 kyr after detrital Th correction; the large uncertainty stems from low ²³⁰Th/²³²Th and underscores the difficulty of dating thin vadose precipitates.

To circumvent open-system behavior, we turned to enamel AMS ¹⁴C. After removing the outer 2 mm, the remaining enamel powder was subjected to 2 % NaClO (48 h) and 1 M acetic acid (24 h) to eliminate organics and secondary carbonates. CO₂ was extracted by H₃PO₄ digestion, graphitised, and measured at the Xi’an AMS Centre on a 3 MV tandem accelerator. The raw ¹⁴C activity (5.54 ± 0.09 pMC, δ¹³C = –17.23 ‰) translates to a calibrated age of 27 501 ± 130 cal yr BP (IntCal20, median probability). Because enamel is virtually collagen-free, this result is considered robust against contamination from exogenous carbon. Bayesian integration of the three chronometers—allowing for U-uptake bias—estimates the death of the animal to 27.5 +1.2/–0.9 kyr BP, coinciding with the Greenland Interstadial 3 (DO 3) warm event within MIS 3.

At the regional scale, this age aligns with a pronounced negative δ¹⁸O excursion recorded in the Didonghe stalagmite 25 km to the west and mirrored by contemporaneous speleothem minima in Yangzi, Furong, Hulu and Qingtian caves. Palynological spectra from the Hanzhong Basin register a synchronous expansion of temperate-subtropical deciduous broad-leaf forest (Quercus, Ulmus, Betula), indicating mean annual temperatures 2–3 ℃ higher and precipitation 15%–20 % greater than today. Such conditions created a dense C₃ forest–wetland mosaic ideal for a specialized browser.

Stable-carbon isotope studies of coeval Stegodon orientalis populations across South China yield a narrow δ¹³C range centered about -16 ‰ (-16.7‰ to -14.7‰), confirming strict C₃ folivory. In contrast, the sympatric Asian elephant (Elephas maximus) displays a broader isotopic envelope (-17.9‰ to -11.9 ‰), reflecting flexible mixed feeding that includes C₄ grasses. We argue that this dietary specialization made S.orientalis particularly vulnerable when monsoon strength waned after 27 kyr BP. Heinrich Stadial 3 and subsequent stadials caused rapid forest fragmentation and southward displacement of subtropical biomes. By the Last Glacial Maximum (LGM), the combined effects of extreme cold (mean annual temperature below 6 ℃) and aridity exceeded the physiological tolerance of these species, leading to regional extinction north of the Yangtze River. Elephas maximus, with its broader ecological niche and smaller body mass, survived in refugial pockets in Yunnan and Guangxi.

The Tianxingyan record thus captures a brief, climate-driven range expansion of Stegodon orientalis into the northern subtropics during a DO warm pulse—a pattern consistent with the final south-to-north dispersal episode proposed for Chinese stegodontids. By integrating precise geochronology with high-resolution palaeoclimate archives, this study demonstrates that millennial-scale variability, rather than long-term orbital forcing, determined the ultimate fate of this emblematic Pleistocene megafauna.