Paleoseasonality During the Early Pleistocene Revealed Through Stable Isotope Analysis of Equus from the Siwalik Sub-Group of Pakistan

Fossil tooth enamel archives the isotopic variability during its formation, an essential tool to reconstruct the paleoseasonal changes during an animal’s life. Stable isotopes of carbon and oxygen from enamel (δ13Cenamel and δ18Oenamel) reveal an animal’s dietary and drinking preferences and are helpful in the reconstruction of paleoclimate and seasonality. The current study attempts to probe these paleoclimatic and seasonal changes during the Early Middle Pleistocene (2.5–1.6 Ma) and their impact on mammals of the Siwalik sub-Group of Pakistan using the intra-tooth analysis of Family Equidae for δ13Cenamel and δ18Oenamel (n = 87). The δ13Cenamel values of the Family Equidae (− 3.1 ± 1.3‰) indicate that the Pleistocene mammals consumed C4 diet (grasses) dominantly. Whereas, δ18Oenamel values of Equidae (0.2 ± 1.5‰) provide evidence for a dry and open habitat where animals were drinking from open evaporating water sources, most preferentially, ponds or streams. A positive correlation between intra-tooth δ13Cenamel and δ18Oenamel indicates that C4 grasses spread more under dry conditions. The higher variations in intra-tooth δ18Oenamel values (4–5‰) indicate an intense seasonal influence on the Siwalik floodplain. Our results conclude that the Early Middle Pleistocene time span (~ 2.5–1.6 Ma) in the Siwaliks was dominated by C4 grasses favored under the dry and highly seasonal climate, as revealed through the intra-tooth isotopic signals.