Quaternary palaeoenvironmental archives of the Indian subcontinent and their imprint on herpetofaunal biogeography: A multi-proxy synthesis

This review presents the first integrated proxy, mechanism and biotic-response framework for the Indian Quaternary, linking the Subcontinent's dense network of palaeoenvironmental archives to the biogeographic trajectory of its endemic herpetofauna. Speleothem δ18O records, Arabian Sea and Bay of Bengal sediment cores, Karewa and peninsular lake sequences, Siwalik and Narmada alluvium, and Kurnool cave deposits together document Indian Summer Monsoon (ISM) variability on orbital, millennial, centennial and historical timescales (the historical band here denoting the past ∼2000 years, resolved by dated speleothem and documentary records). Against this proxy backbone, the fossil and molecular phylogeographic record of Indian amphibians and reptiles is evaluated as a biogenic assemblage here, the body of biological evidence (fossils, subfossils and the phylogeographic signatures of living taxa) that, like pollen or foraminifera, records past environmental conditions that complements geological and climatological archives. Three patterns emerge. At orbital scale, ISM variability aligns with Plio–Pleistocene diversification slowdowns in Western Ghats ranoids and with the Late Pliocene lineage divergence of the Himalayan toad Duttaphrynus himalayanus across the Thakkhola basin. Abrupt Holocene excursions, including the 8.2 ka and 4.2 ka events, are resolved at high precision in speleothem and marine archives but remain untested against coalescent demographic inference in Indian herpetofauna. Late Pleistocene aridity, most severe at the Last Glacial Maximum, coincides with community-level impoverishment in peninsular cave faunas at Kurnool, although the available evidence establishes co-occurrence rather than a demonstrated causal role for aridity relative to co-varying thermal and vegetation change. Three proxy-calibrated research priorities follow: microvertebrate taphonomy in Narmada and Karewa sequences, population genomics tied to speleothem chronology, and species-distribution hindcasting to the LGM, mid-Holocene and 4.2 ka intervals. The synthesis contributes to a biogenic assessment of Quaternary-to-Recent climate impacts on life on the Indian Subcontinent, aligned with UN Sustainable Development Goals 13 (Climate Action) and 15 (Life on Land), and supports future projections of amphibian and reptile response to ongoing change.