Palaeodietary and palaeoclimatic reconstruction for late miocene hipparionines from the siwaliks of pakistan

Abstract

Dental materials of three hipparionine species from Dhok Pathan Formation (late Miocene) has been utilized in this study to reconstruct the palaeodiet and palaeoecology by using stable isotope analyses of carbon and oxygen of tooth enamel carbonate. A gradual increase in hypsodonty and complexity in plications indicate the drier environments with hard and tough food available during the late Miocene. The late Miocene hipparionines were expected to have inhabited a mosaic of woodland and grassland with predominant C3 vegetation which latter shifted to C3/C4 grasses. For this purpose, fifteen dental samples (Five for each Hipparion species) from well dated late Miocene localities between 8.8-7.7 Ma are analyzed. All the δ13C values (V-PDB) are in range of -11.27 to -3.36 which represent that these horses dominantly inhabited C3 vegetation however, the C4 grasses were being indicated as the diet of Hipparionines the latest Miocene. All these species are believed to inhabit more open environment with patchy grasslands. Non-significant differences were observed between the species which explains that the dietary niche of these species was more or less similar. However, the values for carbon isotopes are highly depleted for early hipparionine species (Sivalhippus theobaldi) and less depleted for succeeding species (Sivalhippus perimensis and Cremohipparion antilopinum) which represent dominancy of C4 diet in more open habitat in later species. The values for δ18O are also not significantly different between these species indicating that water intake behavior was also, more or less, same for these species. δ18O (range between -11.4 to -3.8 ) variability may indicate a climatic shift in precipitation source or amount rainfall through time. We suspect that grasslands expanded at the expense of forests towards the latest Miocene while environment became drier and warmer. These analyses also reveal that hipparionines shifted from C3 browsing to mixed C3/C4 and to C4diet at the end of Miocene.