Middle Miocene Environments of the Lower Siwaliks: Taphonomy, Diet, and Paleobiogeographic Links of the Chinji Mammalian Assemblage

Abstract

Background: The Middle Miocene Chinji Formation of the Lower Siwaliks represents a critical window into South Asian paleoecology, capturing faunal and environmental transitions influenced by Himalayan tectonism and monsoonal evolution. Despite abundant vertebrate fossils, integrated analyses of taphonomy, dietary adaptations, and paleobiogeography remain limited, constraining interpretations of habitat structure and intercontinental faunal exchange during this interval. Objective: This study aimed to reconstruct the paleoenvironmental framework of the Chinji Formation by integrating taphonomic observations, mesowear and hypsodonty indices, and comparative faunal data to evaluate depositional context, dietary patterns, and biogeographic affinities. Methods: Fossil specimens from key Chinji localities (Wasnal, Bhilomar, DBAK, Kohetra) were assessed for weathering, abrasion, and element representation. Mesowear and hypsodonty metrics were compiled from new and comparative datasets, and community structure was analyzed using browser-to-grazer ratios and lineage comparisons with coeval Eurasian faunas. Results: The assemblage exhibited moderate weathering and low articulation frequencies, consistent with attritional floodplain accumulation under monsoonal fluvial regimes. Dental morphology indicated a predominance of browsing and mixed-feeding herbivores (browser:grazer ≈ 3:1). Comparative analysis revealed Eurasian affinities at the tribe level (Tragocerotini, Rhinocerotidae) alongside endemic South Asian elements. Conclusion: The Chinji Formation reflects a woodland-dominated, fluvially reworked ecosystem with mixed-feeding herbivore dominance and partial faunal continuity with contemporaneous European assemblages, underscoring climatic and tectonic controls on Miocene biodiversity.