Carbon isotope signature of environmental change found in fossil ratite eggshells from a South Asian Neogene sequence

A >10-m.y.-long sequence of ratite (e.g., ostrich) eggshells from Siwalik Group sedimentary deposits of northern Pakistan and India shows a dramatic (approximately 8 per thousand) increase in the Delta13C in biomineralogic calcite by approximately 4 Ma. Values of Delta13C from ratite eggshell carbonate older than 7 Ma are about the same as those from carbonate from contemporaneous fossil mammal tooth enamel and paleosols. However, after 4 Ma, the ratite eggshell carbonate Delta13C values are approximately 5 per thousand less than these coexisting materials. These findings are evidence of the development of a C3-C4 vegetative mosaic probably mirroring the sedimentologic-edaphic mosaic of the aggrading alluvial plain of the Siwalik depositional system.