Systematic and Palaeoclimatic Investigations of Sivalhippus from the Late Miocene Siwaliks (Pakistan)

A mandible and several isolated upper and lower teeth of a hipparionine horse were discovered and described from late Miocene localities of district Chakwal, Punjab, Pakistan. The morphometric analysis of the samples led to identify the genus Sivalhippus. Sivalhippus lived in the Siwaliks from 10.7 to 5.8 Ma. The stable isotope analysis of the carbon and oxygen was used as a palaeodietary and palaeoclimatic proxy. The enamel hypoplasia analysis of the samples revealed a moderate level of stress faced by the Sivalhippus as a result of seasonality and climate change. All the findings of our study represent that Sivalhippus endeavored a mosaic of woodlands and grasslands with increasing consumption of C4 grasses in their diet. Our study suggests that increase in hypsodonty index in Sivalhippus was due to the increasing dietary stress of coarser dietary material invading the region with a shift from C3 to C4 grasses.