The Piram Island fossil mammals revisited: Implications for age and palaeoecology

Piram (Perim) Island of Kathiawar (Gujarat) is well known for its preserved wealth of fossil vertebrates since the early 18th century. Broadly, these vertebrates have been considered to be equivalent to the Dhok Pathan stage of the Middle Siwaliks (~9.8-3.5 Ma). Based on earlier finds and recent field work, we describe additional fossil mammals, including the first report of a rodent from these sediments. Also, we discuss the biostratigraphy and palaeoecology of Piram in the light of the latest available Siwalik mammalian biochronology and stable carbon and oxygen isotope analyses. We can now place these highly fossiliferous sediments at ~8.7 Ma based on the first occurrence (FO) of the hipparionine equid Sivalhippus perimensis and the last occurrence (LO) of the rodent Democricetodon fejfari. Our carbon isotopic data reveal that most of the mammals (bovids, proboscideans, rhinoceratids and giraffids) were dominantly C3 browsers and lived in tropical forests and wet to dry woodlands, whereas Sivalhippus perimensis had a wider range of diet and habitat, ranging from C3 browsing in the tropical forest and wet-dry woodland to mixed C3 and C4 feeding in water stressed wooded grassland. Further, the intra-tooth oxygen isotope values recovered from two high crowned Sivalhippus perimensis teeth reveal evidence of the existence of monsoon-like seasonality in the Late Miocene around the Kathiawar region of Gujarat. Overall, the carbon isotope data indicate co-existence of strict browsers, mixed feeders, and limited grazers in a mosaic of closed canopy forest, woodland and some grassland patches, while oxygen isotope data suggest environmental heterogeneity.