Palaeoclimate and Dietary Niche of Family Cervidae from the Siwaliks (Pakistan): Does Coeval Occurrence of Species Leads to Niche Partitioning?

Biogeochemistry is crucial to reconstruct the climate, diet, and habitats of extinct animals. The Siwalik sediments of Pakistan exhibit an excellent record of faunal elements, providing an opportunity to explore palaeohabitats of diverse mammalian communities that existed in the Siwaliks. This study is the first to investigate the dietary niche and climatic context of the Siwalik cervids from ~5 Ma to ~2 Ma (early Pliocene to early Pleistocene). Tooth enamel of 25 fossil samples belonging to four different species (R. simplicidens, C. sivalensis, C. triplidens, and C. rewati) was subjected to carbon (δ¹³C) and oxygen (δ¹⁸O) isotope analysis. Family Cervidae shows significantly different average δ¹³C values of −12.2‰, −9.9‰, and 1.0‰ for early Pliocene (~5 Ma), late Pliocene (~3 Ma), and early Pleistocene (~2.2 Ma) time spans, respectively. δ¹³C_enamel values indicate that cervids preferred a close habitat and preferably browsed on C₃ vegetation in forested parts of the fan during the early Pliocene, with the gradual shift toward increasing C₄ vegetation in diet and more open habitat over time. By the early Pleistocene, Siwalik cervids fed entirely on C₄ vegetation in open grassland settings. Such change in the diet seems to be synchronous with increased complexity (increased enamel thickness and hypsodonty) in dentition over time. δ¹⁸O_enamel reveals a significant shift through time with values of −10.0‰, −5.9‰, and 3.7‰ from the early Pliocene, late Pliocene, and early Pleistocene, respectively. Many species of the family Cervidae were coeval and diachronous, possibly justified by the niche partitioning hypothesis.